Project Reports

Accomplishments and what was accomplished under each objective.

(1) Survey of broccoli crop for Alternaria sp.

In the fall of 2023, Co-PI Smart collected 50 A. brassicicola isolates from ABHR outbreaks in NY.  All 50 isolates collected in 2023 were found to be A. brassicicola using species specific PCR primers. We collected more than 500 single conidia isolates in CT, MA, GA, NY, and VA and identified most isolates as A. brassicicola. Using microplate assay based on optical density (OD) measurements to estimate inhibition of spore germination indirectly, we screened 350 A. brassicicola isolates against azoxystrobin. We found that A. brassicicola was sensitive to azoxystrobin with low EC50 values ranging from 0.005 ppm to 0.521 ppm and a median EC50 value of 0.0284 ppm. In addition to A. brassicicola, we found A. alternata in NY in 2021, CT in 2022 and VA in 2022 and 2023. We evaluated fungicide sensitivity using the microplate assay and screened for mutations that confer resistance to QoIs. We found that multiple A. alternata (n = 45) isolates had reduced sensitivity to azoxystrobin. EC50 values ranged from 0.012 to 83.9 ppm, and a median EC50 value of 4.35 ppm. Among 21 A. alternata sequenced at the cytb gene, 19 isolates showed the mutation G143A that confers complete resistance to QoIs.  Studies are still ongoing to screen all A. alternata isolates. This study may explain why QoIs have reportedly failed and enable us to make more informed disease management recommendations.

 (iv) Pathogenicity and aggressiveness of Alternaria isolates collected:

Pathogenicity of the 2023 isolates was not tested, that work was done in 2022

(v) Fungicide sensitivity and fungicide resistance screening:

The Co-PI Smart conducted Boscalid sensitivity test for 76 isolates collected in 2021 and 2023. A group of 48 isolates were found to have reduced sensitivity to boscalid while the remaining 28 were sensitive. This is critical information as growers in NY use the fungicide Endura (active ingredient – boscalid) to control ABHR.

(vi) Population genetics:

The Everhart Lab has developed, multiplexed, and tested primers for amplicon sequencing of single nucleotide polymorphisms (SNPs) identified in A. brassicicola genomes. One 96-well plate has been run using these primers as an initial pilot trial. Additional plates will be run shortly to identify SNPs in isolates. Fragment analysis has also been completed on 142 A. brassicicola isolates from four states (one in CT, one in MA, and two in GA) collected in 2022. In two regions, the fields were less than 10 miles apart, and this study was designed to determine if population structure was more similar among closer fields. The 11 novel microsatellite primers designed in the Everhart Lab were used to describe the population structure. Using these primers, the population structure of A. brassicicola was found to be highly genetically diverse in all fields. Despite the distance between the two field regions, there were very few shared multilocus genotypes between any fields. We hypothesize that there may be multiple introductions of A. brassicicola that caused this population structure and that additional fine-scale sampling will be required to identify clones. Furthermore, while the organic CT and MA fields seem to have more clones present, the two conventional fields in GA are more likely to have sexual recombination occurring, despite only one mating type being present in the fields.

 (vii) Development of diagnostic tools:

The Everhart Lab has developed multiple diagnostic tools for population genetic analysis, population genomics, fungicide resistance, and rapid fungicide sensitivity screening.  The Everhart Lab group developed, tested, and implemented eleven microsatellite primers for fragment analysis to describe the population genetics of A. brassicicola. The primers consisted of 9 trinucleotides, 1 tetra-nucleotide, and 1 hexa-nucleotide primers that ranged between 120 and 360 base pairs. The Everhart Lab group also designed, multiplexed, and tested 148 single nucleotide polymorphism (SNP) primers for amplicon sequencing, ranging from 250 to 400 base pairs. For fungicide resistance gene detection, the Everhart Lab group has also designed and validated primers to amplify partial sequences of the AsSdhB, AsSdhC, and AsSdhD genes to detect mutations that cause resistance to SDHI (succinate dehydrogenase inhibitor) fungicides. Primers were evaluated in NY and GA isolates and detected the H134R mutation in the AsSdhC gene. The Everhart Lab has also developed a diagnostic in vitro assay to screen multiple isolates in less time than the convectional method using petri dishes. The assay was used to screen for sensitivity for azoxystrobin and used in two Alternaria species. It is currently being tested for another fungicide, boscalid, which is an SDHI chemistry. Once the protocol is published it could be replicated by researchers working with these Alternaria species.

(i) Fungicide programs:

During the 2023 field season, we evaluated three conventional fungicide spray programs on two resistant broccoli cultivars ‘Abrams’, ‘Burney’ and a susceptible check ‘Emerald crown’ for Alternaria leaf blight and head rot control. The fungicide programs include Program 1 – Bravo WS, Miravis Prime, Quadris Top; Program 2 – Bravo WS, Priaxor, Inspire Super; and Program 3 – Bravo WS, Quadris top, Bravo WS. These programs were based on results from 2021 and 2022 trials.

Summary of tables: –

  • Significant differences among fungicide programs were observed only on susceptible cultivar ‘Emerald crown’ both in leaf and head disease reduction.
  • Fungicide program 2 (Bravo WS, Priaxor, Inspire Super) was efficacious in reducing leaf and head disease severity and yield loss in Emerald crown. Programs 1 and 2 significantly reduced leaf disease compared to program 3, whereas programs 2 and 3 were efficient in reducing head disease and yield loss as expressed by % marketable weight per plant. 
  • Significant differences were observed among varieties for marketable head number and head weight per plant. Emerald crown had the lowest marketable head number but the highest average head weight per plant. The highest yield as expressed by average head weight is related to the cultivar’s yield potential. There was no difference between programs for both average head weight and marketable head number.
  • No significant difference was observed for the marketable weight per plant.
     
  • Additionally in 2023, we evaluated two OMRI-listed fungicide programs for organic broccoli producers.
  • Two fungicide spray programs were compared on two resistant broccoli cultivars ‘Abrams’, ‘Burney’ and a susceptible check ‘Emerald crown’ for Alternaria leaf blight and head rot control. The fungicide programs include Program 1 – Oso, Kocide, Oso; and Program 2 – three applications of Kocide at a weekly interval. Oso 5% SC and Kocide 2000 fungicides were selected based on their best performance over untreated control in previous year.
  • Summary
  • No significant differences were observed between the two fungicide programs.
  • Significant differences were observed among varieties for leaf area under disease progress curve, last rating of percent head disease, percent marketable weight, number of marketable head and marketable head weight per plant (g). No significant difference was observed for head weight per plant (g).
  • Cultivar Burney showed the lowest disease severity both on the head and leaf. A higher number of marketable head and marketable head weight was also recorded on cultivar Burney.    
  • Mefentrifluconazole (Cevya, BASF Ag Products), currently unregistered for brassica head and stem vegetable group, was evaluated in a RCBD field trial in Painter, VA. Mefentrifluconazole reduced head rot by 93.5% compared to the untreated control and was equally effective as the grower standard (azoxystrobin + difenoconazole). Three cultivars (Burney, Abrams and Emerald Crown) with varying levels of resistance were combined with three different fungicide programs or left untreated and evaluated in a split-plot field experiment in Painter, VA. Without fungicides Burney and Abrams had >40% head rot whereas Emerald Crown had <5%. In both Burney and Abrams, fungicide programs performance was comparable regardless of cultivar and reduced head rot by more than 90% compared to the untreated control. Three cultivars were combined with two organic fungicide programs or left untreated and evaluated in a split-plot field experiment in Painter, VA. Without fungicides Abrams had over 60% head rot wereas Emerald Crown had <15%; Burney had significantly less head rot (<25%) than Abrams. Copper hydroxide alternated with polyoxin d was reduced head rot compared to the untreated in both Abrams and Burney.  A trial examining the control of Alternaria on broccoli offered by conventional fungicides was conducted in the fall of 2023.  Foliar disease pressure was moderate with 33% foliar disease severity in the NTC plots. Disease progressed more slowly, and foliar disease severity was significantly lower in the plots treated with Fontelis 20SC 14 fl oz/A (16%), Topguard 11.8SC 5 fl oz/A (16%), and Quadris Top 29.6SC 12 fl oz/A compared to the non-treated control plots. The remaining treatments were significantly different from the NTC for both foliar disease severity and disease progression except for disease progression in plots treated with Bravo Weather Stik 54SC 1.5 pt/A. Marketable yield was significantly higher than the NTC in plots treated with Quadris Top 29.6SC 12 fl oz/A. No other treatment significantly outyielded the NTC.Biological/Organic Fungicides:  A trial examining the control of Alternaria on broccoli by organic/biological fungicides was conducted in Blacksburg in the fall of 2023.  Foliar disease pressure was moderate to high with 45% foliar disease severity in the NTC plots. Disease progressed more slowly, and foliar disease severity was significantly lower in the plots treated with OSO® 5SC 13 fl oz/A, LifeGard 40WG 4.5/100 gal, and Cueva 10F 2 gal/A compared to the non-treated control plots. All remaining treatments but one (Oxidate 32F 0.5% v/v) were significantly different from the NTC for both foliar disease severity and disease progression. No treatments significantly outyielded the NTC.

(ii) Evaluation of irrigation practices:

Our work on this objective was completed last year.

(iii) Broccoli cultivar trials for ABHR tolerance:

The primary trials were completed in Georgia in Fall 2022 and a publication was recently accepted in Plant Health Progress.  In 2023 an additional trial that was not in the original objectives was undertaken that compared 9 cultivars with selections from the best and worst performing cultivars, in terms of disease resistance, from the previous studies. In this study determined the impact of the growing environment x disease interaction with inoculated and non-inoculated plots.  This study was repeated at the partner institutions in the Eastern US. A manuscript will be prepared from this study using data from all collaborating states.

(iv) The effect of nitrogen fertilizer rate: 

These trials were completed in Georgia in Fall 2022 and we found no significant impact of nitrogen fertilizer rate in either Tifton or Athens, GA locations on ABHR incidence. Results were presented at several grower and scientific conferences.

(v) Evaluation of inoculum sources (weed and seed)

Several isolates of A. brassicicola were cultured from broadleaf dock (Rumex obtusifolius), common lambsquarters (Chenopodium album), and cutleaf evening primrose (Oenothera laciniata).  These were found to be pathogenic on broccoli through pathogenicity testing.

Seeds:
We
characterized Alternaria spp. isolates from commercial broccoli seedlots for their species identity, pathogenicity, and aggressiveness on broccoli and their sensitivity to a quinone-outside inhibitor (QoI) fungicide (azoxystrobin). Two hundred commercial seedlots from two broccoli cultivars, Cultivar 1 (EC; n = 100 seedlots) and Cultivar 2 (ED; n = 100 seedlots) were, evaluated for the presence of A. brassicicola under in vitro conditions using a seedling grow-out assay. Alternaria spp. was detected in 31 and 28% of the commercial seedlots of Cultivar 1 and Cultivar 2, respectively. Ninety-six percent (n = 133) of the isolates formed a cluster with a known Abrassicicola based on a multigene phylogeny, which were later confirmed as A. brassicicola using a species-specific PCR assay. One hundred percent of the A. brassicicola seed isolates (n = 133) were either highly or moderately aggressive on broccoli (cultivar Emerald Crown) based on a detached leaf assay. Sensitivity of representative A. brassicicola isolates (n = 58) to azoxystrobin was evaluated using a spore germination assay, and the EC50 values (effective fungicide concentration [ppm] at which germination of conidia of isolates were reduced by 50% compared to control) for each isolate was determined. A. brassicicola isolates from naturally infested commercial broccoli seeds were sensitive to azoxystrobin with considerably low EC50 values in the range of <0.0001 to 0.33 ppm; however, there were a few isolates (14%) that showed 100-fold reduced sensitivity from the most sensitive isolate (EC50 = 0.0001 ppm). Our results confirm that commercial broccoli seedlots can be naturally contaminated with pathogenic and aggressive A. brassicicola. We also provide evidence for the potential presence of A. brassicicola isolates with reduced azoxystrobin-sensitivity in naturally infested commercial broccoli seedlots, which has never been reported before.

(vi) Economic analysis [Colson (Economist, UGA)]

Multiple years of yield and efficacy data from cultivar, fungicide, irrigation, and nitrogen field trials in Georgia, New York, and Virginia were synthesized with market price data as part of an economic analysis evaluating the balance between cost, efficacy, and revenue for growers considering potential adoption. Previous analysis indicated that most growers perceive themselves as only somewhat to moderately equipped, in terms of chemicals, cultivars, and knowledge, to effectively manage Alternaria leaf blight and head rot (ABHR), highlighting the need for greater scientific evidence on potential management solutions.

Field experiments in Virginia exploring the susceptibility of different varieties to ABHR found significant differences in both efficacy and marketable yield. Economic analysis revealed that high-performing varieties in the Virginia region could yield substantially larger economic returns compared to low-performing varieties, which experienced significant ABHR rates during trials. For instance, the best-performing cultivar compared to the worst-performing cultivars in the trials had an approximately $4,000 difference in revenue per acre due to the substantially lower marketable yield for cultivars highly susceptible to ABHR.

In Georgia and New York, economic analysis of fungicides showed that, relative to untreated control, various fungicide products were effective in reducing the percentage of unmarketable broccoli heads due to ABHR. Among the effective products, there was a clear positive economic return for growers applying the fungicides to their crop, particularly in Georgia, where disease pressures were markedly higher compared to New York. In such conditions, appropriate fungicide application is essential to avoid significant economic losses.

Previous survey data from growers involved in this project revealed that most broccoli producers were uncertain if, or to what degree, excessive nitrogen fertilization might impact loss rates from ABHR. Experimental evidence from New York trials, which considered nitrogen rates 50% below and 50% above the grower standard, showed some yield loss at very low or very high nitrogen application rates. When yields were converted into revenue streams under alternative broccoli prices and considering a range of nitrogen prices from the historical average to the peak nitrogen prices of the past five years, the results indicated that, even when facing record-high nitrogen prices, optimizing the nitrogen rate yielded the greatest revenue-adjusted profit for growers.

A fourth production practice considered was the timing of overhead irrigation. Data from Georgia, considering morning, noon, and evening irrigation, revealed a significant difference in ABHR rates and the percentage of unmarketable broccoli heads. This finding is particularly important economically, as optimizing the timing of irrigation to reduce losses is potentially a win-win for growers, increasing revenue at no additional cost, provided there is sufficient irrigation capacity to water the crop within the optimal irrigation windows.

Overall, the economic analysis underscores the importance of optimizing production systems, including cultivars, fertilization, fungicides, and irrigation. Given the high value of broccoli, measures that effectively reduce ABHR were generally found to increase per-acre profit as the increased revenue generated through reduced losses due to unmarketable broccoli heads outweighs the increased cost of inputs.

opportunities for training and professional development have the project provided:-

The postdoc on the project has attended several workshops for professional development purposes. She also has co-presented with Chris Smart at grower meetings and for a webinar. Ag-clientele have been informed / educated about the current resistance situations in CT, MA, NY, VA, and GA and resistance management options through presentations at annual conferences. Provided ongoing mentoring of two graduate students, one postdoc, and three undergraduate students. The graduate students and postdoc presented their research at various scientific meetings and two students are on track for graduate degree completion in 2025. Three undergraduate students from UConn involved in this project received training in microbiology and molecular genetic techniques. Also involved was postdoc, Roy Davis II, who mentored graduate students and undergraduates on these projects

Project report year 3

Accomplishments and what was accomplished under each objective.

Project goal statement:

Survey of broccoli crops for Alternaria sp. In NY over 119 isolates were collected and identified as Alternaria brassicicola based on PCR amplification using species-specific primers. Considerable variation in aggressiveness was observed with isolates from both species on broccoli, cabbage, kale and collard. In GA Based on our survey of multiple commercial broccoli fields, it was found that nearly 85% of the isolates (n=250) were A. brassicicola and only 15% were identified as A. japonica. Conidial germination assay for a sub-set of isolates on azoxystrobin-amended agar medium indicated that majority of the isolates of both Alternaria species were sensitive at both concentrations (10 and 100 µg/ml). Considerable variation in aggressiveness was observed with isolates from both species on broccoli, cabbage, kale and collard. In VA a total of 269 fungal isolates were collected from symptomatic broccoli in commercial fields, which were later identified as Alternaria spp.

Population genetics: To standardize sample collection in CT, NY, VA, and GA, a sampling protocol was developed and disseminated. This sampling protocol was designed to characterize the amount and pattern of genotypic variation of A. brassicicola in broccoli fields. A total of 373 single spore isolates were obtained from the collection of 521 leaf lesions from five states (CT, MA, NY, VA, GA). The identities of these isolates were confirmed using PCR amplification and gel electrophoresis with the A. brassicicola speciesspecific primers. Preparations have been made for sending samples for amplicon sequencing (AmpSeq). Single nucleotide polymorphisms (SNPs) and microsatellites (SSRs) have been identified to determine if there is any geographic structuring in the populations of A. brassicicola in the eastern United States.

Approximately 300 A. brassicicola isolates that were collected between 2021 and 2022 in CT, MA, NY, VA, and GA were screened for sensitivity to azoxystrobin. Most isolates that were screened are sensitive to azoxystrobin with EC50s lower than one ppm, with the exception of about 25 isolates collected from two fields in VA. The cytb gene has been sequenced for 19 of these isolates, however no known mutations were identified. Screening of A. brassicicola isolates is being repeated for a second time. Once these are completed, screening of A. japonica isolates will commence.

An improved single spore isolation method was used to expedite the collection of A. brassicicola isolates from the leaf lesions collected during the 2022 surveys. Extraction of DNA has also been completed for all single spore isolates from 2022. To identify SNP and SSR loci, the six A. brassicicola genomes (A18, A48, A63, A71, F6A2, F6A9) that were previously assembled as a part of this project in were used. A detection pipeline was developed to use sequence A18 as a reference against which the other five were mapped. Following the detection of variants, flanking sequences were extracted from the data and primers were developed surrounding the SNP loci. Microsatellite (SSR) primers were either designed using WebSAT or taken from previously published sources.  Primers were divided into two groups for SNPs (190 pairs) and SSRs (161 pairs) and pooled using oPools from IDT DNA for amplicon sequencing (AmpSeq). A 96-well plate with representative samples from each state was prepared for an initial AmpSeq trial to determine the attrition rate of the pooled primers.

Development of diagnostic tools: As no known mutations have been identified in any of the isolates collected, a diagnostic tool has not been developed. Instead, focus has shifted to developing and implementing a high-throughput fungicide sensitivity assay to screen multiple isolates using a microplate-based method to analyze approximately 300 A. brassicicola isolates. The microplate method produced similar EC50s to the conventional method based on spore germination assays on petri plates.

(i) Fungicide programs:

NY tested 12 products in a conventional fungicide efficacy trial and 9 products (one of which was the conventional product Bravo) in an organic fungicide efficacy trial. All conventional fungicides, with the exception of a new copper zinc (CuZn) formulation, significantly reduced the disease severity compared with the non-treated controls (NTC). However, no fungicide provided complete control of the disease. NY also evaluated Oso at both the full rate and half rate, and both rates were found to have good efficacy against leaf spot and head blight. In fact, Oso at either rate was not significantly different from Bravo, which was included as a conventional control. GA tested 11products in a conventional fungicide efficacy trial and 9 products (one of which was the conventional product Bravo) in an organic fungicide efficacy trial. Among the conventaional fungicide products, Miravis Prime, Topguard EQ, Luna Sensation, Priaxor, Inspire Super, Quadris Top, Quadris and Switch had significantly lower head rot (%) compared with other products (Fontelis, Endura and Bravo). Head rot (%) ratings for the plots treated with OSO at both rates (13 fl oz and 6.5 fl oz), and Microthiol Dispress sulfur had significantly lower incidence compared to other treatments (Howler, LifeGuard, Theia, Zonix, Kocide-3000-O) and non-treated check. VA conducted a biological fungicide evaluation trial on broccoli in Blacksburg, VA in Fall 2022. Foliar disease pressure was minimal with 4.5% foliar disease severity in the NTC plots.  Disease progressed more slowly, and foliar disease severity was significantly lower in the plots treated with OSO 5SC @ 13 fl oz/A, Guarda 3F @ 3% v/v, and LifeGard 40WG @ 4.5/100 gal compared to the NTC plots.  The remaining treatments were not different from the NTC for both foliar disease severity and disease progression. 

 (ii) Evaluation of irrigation practices:

NY evaluated following treatments in irrigation-timing trial 1) 15 minutes of overhead irrigation at 7 AM; 2) 15 minutes of overhead irrigation at noon; 3) 15 minutes of overhead irrigation at 6:00 PM; 4) no additional overhead irrigation. No significant difference was observed among the treatments. GA conducted similar trial in Athens using Emerald Crown as the variety. All plants received drip irrigation and then four irrigation treatments were implemented: no overhead, overhead irrigation at 6 AM, 12 noon, and 6 PM.  Overall, there was significantly less disease in the no misting and 6 AM misting treatments compared to treatments that received misting during the day and this was reflected in the marketable heads from each plot in both study years. VA conducted one trial evaluating drip vs. overhead irrigation and the effect of leaf wetness period on ABHR.  The trial was inoculated twice by spraying a 1 x 105 CFU suspension at 3 and 6 weeks after transplanting.  No disease was detected therefore no disease data is available.

(iii) Broccoli cultivar trials for ABHR tolerance:

NY evaluated  the response of 28 commercial broccoli cultivars to ABHR disease. Based on the assessments, cultivars (Burney, Belstar, Millenium, Iron man, Diplimat, Imperial, Burgandy) had significantly lower area under diseae progress curve (AUDPC) on head compared with Eastern Crown (a commercial standard). GA evaluated 26 commercial broccoli cultivars at two locations; Athens and Tifton, GA in Fall 2022.  Plots were harvested and head analyzed for disease severity and marketable yields determined.  Disease ratings were similar in both study years, with ‘Belstar’ and ‘Marathon’ having low disease incidence in both locations. VA conducted two cultivar evaluation trials in Blacksburg, VA: in Fall 2022 and Spring 2023. In both assessments lowest foliar disease severity was observed with Vallejo, Avenger, and Emerald Jewel.

(iv) The effect of nitrogen fertilizer rate: 

NY compared five following treatments: 50, 75, 100, 125 and 150% of locally recommended N treatment. Half of the recommended fertilizer was applied at planting for the entire plot of the trial. Six weeks after transplanting, the five nitrogen rate treatments were side dressed. Plants were inoculated with a NY isolate of A. brassicicola conidial suspension containing 2 x 105 conidia/ml after the second N side-dress application. No significant differences were found for all the parameters taken. GA evaluated five levels of nitrogen fertilizer ranging from 50% to 150% of recommended rates for broccoli in GA.  While there were significant differences between fertilizer rate and disease incidence, there were no clear trends evident, with the exception of the lowest N application rate, which had a lower incidence of disease compared to other rates. 

(v) Evaluation of inoculum sources (weed and seed)

Seed as a inoculum source: Natural seed infestation of A. brassicicola in commercial seedlots was investigated. Two hundred commercial seedlots from two broccoli varieties; Emerald Crown (n=100) and Eastern Crown (n=100) were evaluated under in-vitro conditions using seedling grow-out assay (SGO). Seed infestation was detected in 35% (Emerald Crown) and 30% (Eastern Crown) of the commercial seedlots. However, seed-to-seedling transmission varied among seedlots (1% to 15%). Further confirmation of symptoms of A. brassicicola infestation was conducted by isolating pathogen from symptomatic seedlings. Subsequent molecular identification of single spore cultures (n=135) were made by sequencing Alta1 gene and comparing the phylogenetic closedness with diverse Alternaria species. One hundred percent of the isolates formed a cluster with a known A. brassicicola isolate, which was later confirmed using a PCR assay with A. brassicicola-specific primers. Further, one hundred percent of the A. brassicicola isolates were pathogenic on broccoli leaves using a detached leaf-assay. Our results suggest that natural seed infestation with pathogenic A. brassicicola can occur in commercial broccoli seedlots, which could potentially play a role in seasonal outbreaks of ABHR in production fields.

Weed as a inoculum source: We collected 26 isolates collected from non-brassica crops and weeds in and around broccoli production fields.  Non-brassica crop and weed species showing symptoms of ABHR were: wild mustard (11), cutleaf evening primrose (10), purple nutsedge (4), swiss chard (3), lambsquarters (1).  Sixteen isolates from non-brassicas and weeds were pathogenic on at least one brassica crop. Weed species containing pathogenic isolates were: wild mustard (8), cutleaf evening primrose (4), purple nutsedge (4), lambsquarters (1).  These results imply that weed species may be an important source of inoculum leading to ABHR outbreaks.  We are currently collecting isolates from more weed species and we plan on conducting studies into possible seed infestation of weed species.

(vi) Economic analysis [Colson (Economist, UGA)]

Yield and efficacy data from cultivar, fungicide, and nitrogen field trials in Georgia, New York, and Virginia were synthesized with market price data as part of an economic analysis to evaluate potential returns to adoption for growers.  Year one trials in Georgia found a 40% greater revenue for Eastern Crown compared to Imperial despite a greater percentage of unmarketable heads.  Cultivar trials in Virginia found a significantly higher level of revenue from Expo compared to other varieties due to the greater marketable yield observed.  Fungicide trials in Georgia found significantly greater revenue from broccoli grown treated with eight different commercial fungicides compared to nontreated control due to extremely high losses without fungicide treatment.  Although not as extreme, similar findings were found in New York trials but not Virginia trials due to low disease pressure.  Economic analysis of New York nitrogen trials (50%, 75%, 100%, 125%, and 150% N) found similar cost-adjusted revenues per acre for 75%, 100%, and 125% N, and significantly lower cost-adjusted revenue for 50% and 150% N.  The finding is robust to broccoli  price sensitivity analysis.  Results indicate that, even when growers are faced with record nitrogen prices, the loss of yield resulting from under application will reduce grower profitability.  Despite higher than normal costs, optimizing nitrogen for yield is the appropriate strategy based on the field trial findings.

What opportunities for training and professional development have the project provided?

Narrative: (Enter narrative)

Technicians, graduate students and postdocs have interacted with colleagues at other universities during quarterly meetings that are part of the grant, expanding their network and skillset. In NY a high school student and an undergraduate from a local community college are currently working on the project over the summer of 2023 as part of an internship program. This has provided them with the experience of working on a plant pathology project that has an impact for broccoli growers. Hirut Betaw, Roy Davis and Navjot Kaur the postdocs on the project, had the opportunity to present their work at the annual meeting of the American Phytopathological Society (APS) in August 2022 and 2023. PD Dutta, Co-PD Langston, Co-PIs Smart, Everhart, Hoepting and Coolong also presented GA, VA and NY. Post-docs also mentored seven undergraduates, across four states.

Changes/Problems

Narrative: An inadvertent change in potting mix containing high amounts of fertilizer resulted on one planting of brassicas for use in pathogenicity assays to be unusable.  Also, the water sources at our labs were switched to accommodate some buildings being switched to the public water system.  We have found that a new water source we had been using to irrigate brassicas used for pathogenicity assays had a pH of ca. 5.0 which resulted in at least 3 plantings being unusable.  To offset these setbacks a new incubator was purchased which will double the number of pathogenicity bioassays we conduct.

Project Report Year 2

NIFA Report Format 

Report due date: 15 August 2021 

Award Number: 2020-51181-32062 

III. Target Audience 

Narrative: (Enter narrative) 

Primary audience of the project is the brassica producers in eastern US. This includes broccoli producers, packers, shippers, agronomists, crop consultants, farm managers, field workers, seed companies, and dealers; and broccoli storage and shipping/transport personnel and companies. Other targets for dissemination include the broader scientific community concerned with the evolution of fungicide resistance and population genomics of plant pathogens.  Targets also include postdocs, graduate students, and undergraduate students who receive training in microbiology, molecular genetics, genomics, and scientific communication.   

IV. Products 

Product type: Select one: Book Chapter; Book; Conference Paper and Presentation; Journal Article; Other; Thesis/Dissertation; Websites 

Conference presentation 

Hirut B, Day, CTC, Smart CD. (2022) Improving control strategies for Alternaria blight and head rot. Presentation at Plant Health 2022 Pittsburgh, Pennsylvania, August 6-10, 2022 

Status: accepted, NIFA Support Acknowledged: Yes 

Nieto-Lopez EH (presenting author), Cerritos-Garcia D, Koch RA, Doss T, Dutta B, Petkar A, Langston D, Rideout S, Smart CD, Everhart S. 2021. Investigation into the loss of fungicide efficacy for Alternaria leaf blight and head rot of broccoli and cruciferous crops in the Eastern USA. Poster: American Phytopathological Society North Central Division Meeting, virtual. Status: Other; NIFA Support Acknowledged: Yes; NIFA Acknowledged: Yes. 

Species-dependent sensitivity to azoxystrobin observed among causal agents of Alternaria leaf blight and head rot in brassica crops in the eastern US. Poster: American Phytopathological Society Annual Meeting 2022 at Pittsburgh, PA. Status: Accepted; NIFA Support Acknowledged: Yes; NIFA Acknowledged: Yes. 

Petkar, A., Doss, T., Patel, K., Torrance, T., and Dutta, B. 2022. Fungicide sensitivity of Alternaria brassicicola affecting broccoli in Georgia. Poster: Annual Meeting of National Institute of Antimicrobial Resistance Research and Education. May 16, Lincoln, Nebraska. Status: Accepted; NIFA Support Acknowledged: Yes; NIFA Acknowledged: Yes. 

Cassity-Duffey, K., T. Coolong, and B. Dutta. Cultivar trials for Alternaria leaf blight and head rot in  

broccoli. ASHS. July 31, 2022. Chicago, Ill. (Poster). Status: Accepted; NIFA Support Acknowledged: Yes; NIFA Acknowledged: Yes. 

Kaur, N., and Dutta, B. 2022. Seed-to-seedling transmission of Alternaria brassicicola in broccoli.Poster: American Phytopathological Society Annual Meeting 2022 at Pittsburgh, PA. Status: Accepted; NIFA Support Acknowledged: Yes; NIFA Acknowledged: Yes. 

Petkar, A., Doss, T., Patel, K., Torrance, T., and Dutta, B. 2022. Host range, aggressiveness and fungicide sensitivity of Alternaria brassicicola affecting broccoli in Georgia. Poster: American Phytopathological Society Annual Meeting 2022 at Pittsburgh, PA. Status: Accepted; NIFA Support Acknowledged: Yes; NIFA Acknowledged: Yes. 

Webinar: Dutta, B. Update on the national Alternaria project in broccoli. Great Lakes vegetable producers network weekly roundtable, Sep 1, 2021. (Webinar; invited) 

Journal Article 

Nieto-Lopez EH, Cerritos Garcia D, Koch Bach RA, Petkar A, Smart C, Hoepting C, Langston D, Rideout S, Dutta B, Everhart SE. 2022. Species identification and fungicide sensitivity of fungi causing Alternaria Leaf Blight and Head Rot in cole crops across the Eastern U.S.  Status: Accepted for publication with Plant Disease Journal. NIFA Support Acknowledged: Yes; NIFA Acknowledged: Yes. 

Cassity-Duffey, K, T. Coolong, and B. Dutta. 2022. Evaluation of the effect of timing of simulated leaf wetness on disease severity in Alternaria leaf blight and head rot in broccoli, Oconee County, GA 2021. Plant Disease Management Report. 16:V153. Support Acknowledged: Yes; NIFA Acknowledged: Yes. 

Kaur, N., and Dutta, B. 2022. Evaluation of fungicide programs for the management of Alternaria leaf blight and head rot in broccoli in Tift County, Georgia, 2021. PDMR 16:V169. 

Dutta, B., and Kaur, N. 2022. Evaluation of organic fungicides for the management of Alternaria leaf blight and head rot in broccoli in Tift County, Georgia, 2021. PDMR 16:V130 

Dutta, B. and Petkar, A. 2021. Management of Alternaria blight and head rot in brassica. Vegetable and Specialty Crop News, June 2021. 

V. Other Products 

For each product, enter the following information: 

Product type: Select one: Audio or Video; Data and Research Material; Database; Educational Aids or Curriculum; Evaluation Instruments; Instrument or Equipment; Model; New Germplasm; Other; Physical Collection; Protocol; Software or NetWare; Survey Instrument 

Description: (Enter 1-3 short sentences should be used to describe what the product is, what activity it resulted from, and whom it benefitted.) 

Product type: Protocol. “DNA minipreps from fungi: Adapted for Alternaria”. This product is a protocol for a quick and cost-effective method for extracting DNA from our Alternaria isolates that resulted from the molecular identification objective. This work benefitted all PIs and associated personnel involved in this study that are responsible for isolating and identifying Alternaria species. 

Product type: Protocol. “Alternaria specific primer protocol”. This product is a protocol that describes how to use species-specific diagnostic primers to identify Alternaria isolates and obviating the need for sequencing. This resulted from the molecular identification objective. This work benefitted all PIs and associated personnel involved in this study that are responsible for isolating and identifying Alternaria species. 

A webpage (https://alternariabroccoliproject.uga.edu/) related to the project was created and has been regularly updated for the information related to the project for the stakeholders. 

VI. Accomplishments and what was accomplished under each objective. 

Project goal statement:  

Survey of broccoli crops for Alternaria sp.  

In GA, a total of 163 isolates were collected from ten commercial broccoli fields in 2021-2022 season in Georgia from three predominant broccoli growing counties (Colquitt, Grady, and Tift Counties). In NY, over a dozen broccoli fields were surveyed, and four fields were identified that had Alternaria outbreaks. Alternaria isolates (n=119) were collected from four fields in four counties across NY including Niagara, Orleans, Ontario, and Broome Counties. In VA, over 160 Alternaria isolates were collected over 2021-2022 from different brassica species and weeds.  

Molecular identification through PCR amplification and sequencing of Internal Transcribed Spacer (ITS):  

To determine the identity of the causal agents of ABHR along the Eastern Seaboard and test the hypothesis that a novel Alternaria subspecies is also a causal agent of ABHR along the Eastern Seaboard, we utilized PCR amplification and multi-locus phylogenetic analysis on a subset of collected isolates from each region (NY, VA and GA). Our results suggest that thus far, only A. brassicicola and A. japonica are responsible for causing ABHR in the target region. Surprisingly, A. japonica was only identified from the isolates that were collected in Georgia. In all three states, more than 90% of the isolates were identified as A. brassicicola. Additionally, we identified single nucleotide polymorphisms (SNPs) in several of our phylogenetic loci, including the major allergen (Alt a1) and ATPase, in the subset of our isolates, suggesting there is geographic structuring of A. brassicicola. Second, we verified the efficacy of a previously published set of Alternaria diagnostic primers for rapid identification of each of our isolates, obviating the need for sequencing. Isolates that do not amplify at any of the diagnostic primers are continued to be sequenced at the ITS locus to ensure proper identification.  

Pathogenicity and aggressiveness of Alternaria isolates collected 

Alternaria isolates from GA were tested for their pathogenicity and aggressiveness on detach leaves of broccoli, cabbage, kale and collards.  These isolates were highly aggressive on broccoli (65%), cabbage (46%) and collard (44%) than on kale (8%). In NY, all 119 newly collected isolates were tested for pathogenicity on detached leaves of broccoli, cabbage, cauliflower, kale and collard crops.  Each isolate x crop was replicated three times. Percent disease on each leaf was assessed five days post-inoculation. Broccoli and collards were the two plants most susceptible to all A. brassicicola isolates while cabbage and cauliflower were least susceptible to all isolates. Significant variation among isolates was observed in aggressiveness towards the crops, and the most aggressive isolates were found to be most aggressive on all crops while least aggressive isolates were found to be least aggressive on all crops. In VA, Alternaria isolates are being tested for their pathogenicity and aggressiveness on broccoli, cabbage, collard and kale. 

(v) Fungicide sensitivity and fungicide resistance screening 

In GA, conidial germination assay for a sub-set of isolates on azoxystrobin-amended agar medium indicated 100% of the isolates (n=145) were sensitive at both concentrations (10 and 100 µg/ml). Fungicide sensitivity assay for A. japonica is underway. In addition, Co-PI Everhart have screened 15 A. brassicicola (five each from NY, VA and GA) and seven A. japonica (all from Georgia) isolates for sensitivity to azoxystrobin. These isolates represent historical collections (isolated prior to the use of QoI fungicides) and new collections. Thus far, we have detected a range in EC50 values, suggesting that some of the isolates are intermediately sensitive to azoxystrobin, but none are resistant. We are currently developing a microplate fungicide sensitivity assay based on colorimetric changes of the dye. This high throughput assay will enable us to screen multiple isolates at a time and get the results in less time. To screen for fungicide resistance in A. brassicicola isolates, we used previously published primer sets that target the known point mutations in the cytb gene that are known to confer QoI resistance in ascomycete pathogens. None of the three known point mutations that confer QoI resistance are present in the 15 A. brassicicola isolates that we used in the phylogenetic analysis and fungicide sensitivity screening. We are currently in the process of optimizing primers that target the cytb gene in A. japonica so that we can screen those isolates for QoI resistance. 

Population genetics:  

An efficient and cost-effective DNA extraction procedure has been optimized for A. brassicicola and all collected isolates have extracted DNA thus far. In order to identify SNPs in our target Alternaria species, we first need to sequence three to four genomes for each species. Currently, we already sequenced six A. brassicicola genomes, and assembled and annotated them. We are currently in the process of mapping the raw reads back to a JGI-generated reference to call SNPs and create a pipeline for understanding the genetic diversity.  

Development of diagnostic tools: None of the three known point mutations that confer QoI resistance are present in the 15 A. brassicicola isolates that we used in the phylogenetic analysis and fungicide sensitivity screening. Before diagnostic tools can be developed to rapidly screen for fungicide resistance, we need to understand the genetic mechanism behind the resistance. To this end, we are continuing to screen Alternaria isolates for the point mutations in the cytB gene. Additionally, we are also generating QoI-resistant A. brassicicola mutants in the lab to verify that we can expect to find the known mutations in the cytB genes in resistant isolates. 

(i) Fungicide programs:  

In GA, six Organic Material Review Institute (OMRI)-listed fungicides were evaluated for the management of Alternaria leaf blight and head rot in broccoli (cv. Emerald Crown) in Tift County. Final disease severity was observed on Oct 20, 2021 with significantly higher foliar severity in all treatments and control plots except for Fontelis (conventional fungicide control). By Nov 1, 2021, disease progressed gradually and none of the treatments including the non-treated check displayed effective disease control. AUDPC values were significantly higher for Double Nickel compared to other treatments and the non-treated check. Furthermore, we also evaluated 11 conventional fungicides for the management of Alternaria leaf blight and head rot in broccoli in Tift County. Based on final disease assessment, disease severity was significantly higher for Switch, Quadris and non-treated check compared to Fontelis, Miravis Prime, Topguard EQ, Bravo Weather Stik, Luna sensation and Priaxor. AUDPC values followed the similar trend as non-treated check, Quadris and Switch had significantly higher values than Fontelis, Miravis Prime, and Topguard EQ.  

In NY, during the 2021 season, conventional fungicides were screened: 12 treatments  were applied four times starting just prior to artificially inoculating with A brassicicola. Cultivar emerald crown broccoli was used and each treatment was replicated four times in a randomized complete block design. All conventional fungicides significantly reduced the disease severity compared with the non-treated control.  

In NY, OMRI-listed fungicides were also screened in a separate experiment. A total of 9 treatments including 6 OMRI-listed fungicides, 2 conventional fungicides and one non-sprayed control were compared for Alternaria leaf blight and head rot. Among the OMRI-listed fungicides, broccoli plants treated with OSO 5%SC had the lowest disease severity. 

 (ii) Evaluation of irrigation practices:  

In GA, an irrigation timing trial was conducted in the Athens location using Emerald Crown as the variety.  All plants received drip irrigation and then four irrigation treatments were implemented: no overhead, overhead irrigation at 6 AM, 12 Noon, and 6 PM.  No significant differences were determined in total yield between misting treatments, but significant differences were determined in the percent disease incidence, number of heads harvested per plot, and marketable heads from each plot.  Overall, there was significantly less disease in the no misting and 6 AM misting treatments compared to treatments that received misting during the day and this was reflected in the marketable heads from each plot. Even with high disease pressure, 67% of heads harvested from the drip irrigated plot were deemed marketable 

In NY, in order to determine the role of timing of irrigation in disease severity, four overhead irrigation treatments were compared. Treatments were 1) 15 minutes of overhead irrigation at 7 AM; 2) 15 minutes of overhead irrigation at Noon; 3) 15 minutes of overhead irrigation at 6:30 PM; 4) no additional overhead irrigation. No significant difference was observed among the treatments. In VA, we conducted a trial evaluating drip vs. overhead irrigation and the effect of leaf wetness period on disease incidence and severity. We did not observe differences between treatments in this trial. We are currently planning on conducting another irrigation trial in Fall of 2022. 

(iii) Broccoli cultivar trials for ABHR tolerance:  

In GA, varieties (n=26) were screened for resistance to A. brassicicola in Athens and Tifton, GA in Fall 2021.  Varieties with low disease in each location included: Marathon, Belstar, Vallejo, and Emerald Pride.  Varieties with low resistance and high disease included Eastern Crown, Mellinium and Asteroid.  

In NY, a field experiment was conducted to determine response of 27 commercial broccoli cultivars to disease. The six-weeks old seedlings were then transplanted mechanically at Research South farm in Cornell Agricultural Research Experiment Station, Geneva, NY. Cultivars were replicated four times using randomized complete block design. Significant difference was observed in susceptibility among the broccoli cultivars with ‘BC 1611’, ‘Montebello’, and ‘Astroid’ being the least susceptible and ‘Green Magic’, ‘Emerald Star’ and ‘Lieutenant’ the most susceptible. A weak negative correlation was observed between AUDPC value and heading days after transplant (-0.24); the negative correlation indicating the earlier the heading date, the more was the disease percentage. In VA, Co-PD Langston and Co-PI Rideout are currently assessing and harvesting a 26 cultivar broccoli trial that has moderate/severe disease pressure. 

(iv) The effect of nitrogen fertilizer rate:   

In GA, a nitrogen fertilizer rate trial was conducted in Tifton and Athens locations using Emerald Crown as the standard variety.  Five levels of nitrogen fertilizer were applied ranging from 50% to 150% of recommended rates for each locationNo significant differences between fertilizer rate and disease were found.  However, higher yields were obtained in the Athens location. 

In NY, five treatments were compared to determine the effect of nitrogen fertility for severity of the disease. The treatments were 50, 75, 100, 125 and 150% of locally recommended N treatment. Half of the recommended fertilizer was applied at planting for the entire plot of the trial. For leaf AUDPC, plots fertilized with 100% N had significantly lower value compared to 50% N treated plots.  

In VA, Co-PD Langston and Co-PI Rideout conducted two trials determine the effect of nitrogen fertility on disease severity.  In the Fall 2021 trial, no significant differences among fertility treatments (50, 75, 100, 125 and 150% of locally recommended N treatment) were observed, but the data did trend towards lower rates of nitrogen having higher disease levels as observed in NY.  

(v) Evaluation of inoculum sources (weed and seed) 

We determined the ability of seed-to-seedling transmission of A. brassicicola in broccoli using artificial infestation of seeds under in-vitro conditions. Seeds (cv. Emerald Crown) were inoculated via vacuum infiltration of conidial suspension (1 × 105 spores/ml). Based on our results, seed-to-seedling transmission of A. brassicicola in broccoli can occur as 100% of the inoculated seedlot transmitted the pathogen indicating seeds could be potential source of inoculum. 

Furthermore, we also explored the effect of the seed inoculum density of A. brassicicola on seed-to-seedling transmission in broccoli. For this experiment, we tested 6 different treatment levels with varying inoculum density including control. Artificial infested seedlots were generated via vacuum infiltration method and SGO assay was conducted as described above. The treatments included: T1 = Control, T2 = 1 × 101, T3 = 1 × 102, T4 = 1 × 103, T5 = 1 × 104, T6 =1 × 105 conidia/ml. Seed germination was impacted and significantly reduced at inoculum level of ≥104 conidia/ml in all the seedlots as compared to the control lot. Consistent seedling transmission occurred at inoculum level of ≥104 conidia/ml in the artificially infested seedlots. We also determined if the difference in the aggressiveness of the A. brassicicola can impact the seed germination and seedling transmission in broccoli. Our study showed that regardless of the variation in the aggressiveness of the A. brassicicola isolates, seed germination and seedling transmission was impacted. We also evaluated commercial seedlots for natural infestation of broccoli seeds with Alternaria. We recovered 73 isolates from 100 commercial broccoli seedlots, which was further confirmed as Alternaria spp.  

In terms of weeds as a source of inoculum, we have collected and isolated Alternaria spp. from cutleaf evening primrose, nutsedge and wild brassica. An isolate found in nutsedge tested positive for A. brassicicola. Currently, more studies are being conducted to verify the other isolates pathogenicity on brassicas species.  

(vi) Economic analysis [Colson (Economist, UGA)] 

Co-PI Colson is currently conducting economic analysis on field trials conducted in GA, NY and VA for 2021 and 2022 seasons. 

What opportunities for training and professional development have the project provided? 

Narrative: (Enter narrative) 

In NY, technicians and postdoc have interacted with colleagues at other universities during quarterly meetings that are part of the grant, expanding their network and skillset. Three high school students worked on the project over the summer as part of an internship program. This has provided them with the experience of working on a plant pathology project that has an impact for broccoli growers. They really enjoyed seeing all the different broccoli cultivars. Hirut Betaw, the postdoc on the project, had the opportunity to present her work at the annual meeting of the American Phytopathological Society in August 2022. Co-PIs Smart and Hoepting also present the work at grower meetings across NY. This project has thus far provided training for two PhD students, one of whom presented his research at a scientific meeting this summer. Another PhD student submitted an article to Plant Disease Journal as a short communication and it was accepted for publication with minor revisions and will be presenting a poster at American Phytopathological Society annual conference 2022. Also involved is a postdoc, Rachel Koch, who has mentored a graduate student on this work thus far. 

Changes/Problems 

Narrative: Changes/Problems 

Narrative: The greatest challenge has been moving to Blacksburg and dealing with the remnants of COVID-19 safeguards that have slowed this process.  Spring 2022 trials evaluating irrigation and fertility were damaged by groundhog feeding.  We plan on conducting trials in Fall 2022 in a field that has not shown groundhog feeding damage in previous years. The researchers were unaware that groundhogs would feed on broccoli until the Spring 2022 irrigation and fertility trials. 

Project report Year 1