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Gray mold and anthracnose fruit rot are two of the most important diseases threatening strawberry production in the United States. Managing these diseases is critical, but difficult without understanding how the fungus causing each disease operates. Improvements in design technology and computer processing power have enabled us to create a new generation of informational resources that explain disease development in a new and exciting way. High-definition photos and time-lapse videos help us recognize and diagnose diseases from their first appearance in the field. Through illustrations and animations, concepts, such as disease cycles, can be explained more effectively. Free availability of these materials on websites and social media makes them accessible to growers, agents, and specialists. Through these materials we can clarify and justify current management practices so that growers can more effectively combat diseases in the field. Using gray mold and anthracnose fruit rot as an example, we created photo galleries and updated, visually stimulating disease cycles for continued and improved grower training. [ABSTRACT FROM AUTHOR]

Although Botrytis fragariae was only recently identified as a new Botrytis species that causes strawberry gray mold, its prevalence extends to many states of the eastern United States. Compared with B. cinerea, which is known to be the causal agent of gray mold on many crop plants including strawberry, B fragariae appears to have specifically adapted to strawberry and exhibits distinct fungicide sensitivity. This is the first presentation of a high-quality genome assembly of B fragariae with gene annotation based on sequence homology and deep transcriptome data. The genome sequence information from B. fragariae is expected to help reveal genomic features underlying its host specialization and evolution of distinct fungicide resistance and other novel pathogenicity mechanisms. [ABSTRACT FROM AUTHOR]

Resistance to fludioxonil in Botrytis cinerea and B. fragariae was previously found to be linked to either overexpression of the drug efflux pump atrB activated by mutations in transcription factor mrr1 or to mutations in the osmoregulation gene os1. In the present study, isolates of B. cinerea, Botrytis group S, or B. fragariae collected from strawberry fields in the United States were resistant to fludioxonil with half-maximal effective concentration values ranging from 0.04 to 0.43 µg/ml for B. cinerea, 0.03 to 1.03 µg/ml for Botrytis group S, and 0.28 to 3.48 µg/ml for B. fragariae. Analyses of mrr1 sequences revealed various mutations linked to fludioxonil resistance in B. cinerea and Botrytis group S isolates. However, no mutations in mrr1 correlated with atrB overexpression-mediated resistance in B. fragariae isolates. Neither nucleotide variations in the 1,370-bp upstream region of atrB nor increased atrB copy numbers could explain the atrB overexpression in these B. fragariae isolates. Mutations in os1 conferred resistance to iprodione in B. cinerea and Botrytis group S isolates; none correlated with resistance to fludioxonil in B. fragariae. In contrast to European isolates, U.S. B. fragariae isolates contained a 3-bp insertion in the coding region of os1. These isolates were more sensitive to osmotic stress but it is unclear whether the insertion is responsible for this phenotype. Our findings suggest that atrB overexpression-associated fludioxonil resistance is an across-species mechanism of resistance to fludioxonil that can be induced by mutations in mrr1 and other, still-unknown mechanisms. [ABSTRACT FROM AUTHOR]

Botrytis cinerea, the causal agent of gray mold disease, is one of the most important pathogens of strawberry. Its control in commercial strawberry fields is largely dependent on the application of fungicides during bloom and fruit maturation. The hydroxyanilide fenhexamid is one of the most frequently used fungicides in the southeast of the United States for gray mold control. It inhibits the 3-ketoreductase (Erg27) of the ergosterol biosynthesis pathway and, due to this site-specific mode of action, is at risk for resistance development. Single-spore isolates were collected from 11 commercial strawberry fields in North and South Carolina and subjected to a conidial germination assay that distinguished sensitive from resistant phenotypes. Of the 214 isolates collected, 16.8% were resistant to fenhexamid. Resistance was found in three of four locations from North Carolina and in four of seven locations from South Carolina, indicating that resistance was widespread. Mutations in Erg27 (T63I, F412S, F412C, and F412I) were associated with resistance, with F412S the predominant and most widespread mutation. In this study, mutations T63I and F412C in field isolates of B. cinerea are described for the first time. Detached fruit studies showed that field rates of Elevate 50 WDG (fenhexamid) controlled sensitive but not resistant isolates carrying any of the four mutations. Resistant isolates produced the same lesion size and number of sporulating lesions on fruit sprayed with Elevate 50 WDG as on untreated controls, showing the fungicide's loss of efficacy against those isolates. A rapid polymerase chain reaction method was developed to quickly and reliably distinguish isolates sensitive or resistant to fenhexamid in the Carolinas and to determine the mutation associated with resistance. The presence of fenhexamid-resistant strains in B. cinerea from strawberry fields in the Carolinas must be considered in future resistance management practices for sustained gray mold control. [ABSTRACT FROM AUTHOR]

Strawberry production in Florida and South Carolina is affected by two major diseases, anthracnose fruit rot (AFR) and Botrytis fruit rot (BFR), caused by Colletotrichum acutatum and Botrytis cinerea, respectively. The effective management of both diseases traditionally relied on weekly fungicide applications. However, to improve timing and reduce the number of fungicide sprays, many growers follow the Strawberry Advisory System (StAS), a decision support system for forecasting fungicide applications based on environmental conditions and previously developed models. The objective of this study was to perform a meta-analysis to determine the effectiveness of the StAS for AFR and BFR management compared with a calendar-based spray program. Thirty-nine trials were conducted from 2009 to 2014 in Florida and South Carolina commercial strawberry fields. Meta-analysis was conducted to quantify the treatment effects on four effect sizes, ail based on the difference in response variables for StAS and the calendar-based treatments in each trial. The mean difference in BFR incidence, AFR incidence, yield, and number of marketable fruit between the two treatments was not significantly different from 0 (P < 0.05). However, the number of fungicide applications per season was reduced by a median of seven when using the StAS, a 50% reduction in sprays compared with the calendar-based approach. Effect sizes were not influenced by location or the favorability of the environment for disease development. These findings indicate that use of StAS in commercial fields is effective in controlling fruit rot diseases with no reduction in yield while substantially reducing fungicide applications. [ABSTRACT FROM AUTHOR]

The sensitivity to seven chemical classes of fungicides was investigated in 1,810 Botrytis cinerea isolates collected from strawberry blossoms and fruit in 181 strawberry fields from seven southern states in the United States across 2 years. Ten isolates were examined from each field. Fungicide sensitivity assays were carried out based on visual assessment of diametrical mycelial growth after 4 days of incubation on media amended with discriminatory doses of fungicides in microliter plates. Results of visual assessments were verified with selected isolates using a previously published germination assay and by inoculating representative isolates with resistant phenotypes on fungicide-sprayed fruit. The overall resistance frequencies of 750 isolates collected in 2012 for thiophanate-methyl, pyraclostrobin, boscalid, cyprodinil, fenhexamid, iprodione, and fludioxonil were 76, 42, 29, 27, 25, 3, and 1%, respectively. Frequencies of 1,060 isolates collected in 2013 were 85, 59, 5, 17, 26, 2, and 1%, respectively. Resistance to thiophanate- methyl and pyraclostrobin was found in virtually every location in both years, whereas resistance to iprodione and fludioxonil was rarely found. Resistant isolates were resistant to either one (23%), two (18%), three (19%), four (14%), five (3%), or six (0.1%) chemical classes of fungicides in 2012. In 2013, this distribution was 24, 29, 26, 8, 2, and 0.3%, respectively. Multifungicide-resistant isolates of B. cinerea were widespread in southern states and evidence suggests that the frequency of isolates with multifungicide resistance increased from 2012 to 2013. The data also show that fungicide resistance in B. cinerea was already present in blossoms, indicating that resistance management needs to be implemented early in the season. [ABSTRACT FROM AUTHOR]

Gray mold disease of blackberry and strawberry is caused by Botrytis cinerea and B. caroliniana in the southeastern United States. In this study, methods to distinguish both species were established and their prevalence was determined in commercial blackberry and strawberry fields. Using DNA from B. cinerea and B. caroliniana reference strains, a species-differentiating polymerase chain reaction (PCR) amplification was developed that amplified G3PDH gene fragments of two different sizes depending on the species. The PCR is performed with three primers (two species-differentiating forward primers and one universal reverse primer) and amplified a 238-bp product from B. cinerea and a 536-bp fragment from B. caroliniana reference isolates. A total of 400 Botrytis isolates were collected from 6 commercial blackberry and 11 strawberry fields of the Carolinas and identified to the species level by the new PCR method. Both Botrytis spp. were identified in blackberry and strawberry fields, but B. caroliniana was less common than B. cinerea. Only 33 of 202 isolates from blackberry fields were identified as B. caroliniana, and the majority of these iso-lates came from two fields in South Carolina. Only 1 of 198 isolates from strawberries was identified as B. caroliniana, and this isolate was found in central North Carolina. B. cinerea but not B. caroliniana iso-lates sporulated on potato dextrose agar and Kings medium B. Our results show that B. cinerea and B. caroliniana coexist in at least some commercial blackberry and strawberry fields of the Carolinas, with B. cinerea being the more prevalent species. [ABSTRACT FROM AUTHOR]

Sterol demethylation inhibitor (DMI) fungicides continue to be essential components for the control of brown rot of peach caused by Monilinia fructicola in the United States and worldwide. In the southeastern United States, resistance to DMIs had been associated with overexpression of the cytochrome P450 14α-demethylase gene Mf CYP51 as well as the genetic element Mona, a 65 bp in length nucleotide sequence located upstream of Mf CYP51 in resistant isolates. About 20 years after the first survey, we reevaluated sensitivity of M. fructicola from South Carolina and Georgia to propiconazole and also evaluated isolates from Alabama for the first time. A total of 238 M. fructicola isolates were collected from various commercial and two experimental orchards, and sensitivity to propiconazole was determined based on a discriminatory dose of 0.3 μg/ml. Results indicated 16.2, 89.2, and 72.4% of isolates from Alabama, Georgia, and South Carolina, respectively, were resistant to propiconazole. The detection of resistance in Alabama is the first report for the state. All resistant isolates contained Mona, but it was absent from most sensitive isolates. It was unclear if the resistance frequency had increased in South Carolina and Georgia. However, the resistance levels (as assessed by the isolate frequency in discriminatory dose-based relative growth categories) did not change notably, and no evidence of other resistance genotypes was found. Analysis of the upstream Mf CYP51 gene region in the resistant isolate CF010 revealed an insertion sequence described for the first time in this report. Our study suggests that current fungicide spray programs have been effective against increasing resistance levels in populations of M. fructicola and suppressing development of new resistant genotypes of the pathogen., Competing Interests: The author(s) declare no conflict of interest.

Gray mold in strawberry is caused by multiple species of Botrytis , including Botrytis cinerea , B. pseudocinerea , B. fragariae , and B. mali . The species B. cinerea and B. fragariae are widespread in production regions of the eastern United States and Germany, and their distinction is important for disease management strategies. Currently, the only way to differentiate these species in field samples is by PCR, which is time consuming, labor intensive, and costly. In this study, a loop-mediated isothermal amplification (LAMP) technique was developed based on species-specific NEP2 gene nucleotide sequences. The designed primer set specifically amplified B. fragariae DNA and no other Botrytis spp. ( B. cinerea , B. mali , and B. pseudocinerea ) or plant pathogens. The LAMP assay was able to amplify fragments from DNA extracted from infected fruit using a rapid DNA extraction protocol, confirming its ability to detect low amounts of B. fragaria DNA from field-infected fruit. In addition, a blind test was performed to identify B. fragariae in 51 samples collected from strawberry fields in the eastern United States using the LAMP technique. The B. fragariae samples were identified with a reliability of 93.5% (29 of 32), and none of the B. cinerea , B. pseudocinerea , or B. mali samples included in the test were amplified in 10 min. Our results show that the LAMP technique is a specific and reliable method for the detection of B. fragariae from infected fruit tissue and can help to control this important disease in the field., Competing Interests: The author(s) declare no conflict of interest.

Although Botrytis fragariae was only recently identified as a new Botrytis species that causes strawberry gray mold, its prevalence extends to many states of the eastern United States. Compared with B. cinerea , which is known to be the causal agent of gray mold on many crop plants including strawberry, B. fragariae appears to have specifically adapted to strawberry and exhibits distinct fungicide sensitivity. This is the first presentation of a high-quality genome assembly of B. fragariae with gene annotation based on sequence homology and deep transcriptome data. The genome sequence information from B. fragariae is expected to help reveal genomic features underlying its host specialization and evolution of distinct fungicide resistance and other novel pathogenicity mechanisms.

The fungal genus Colletotrichum includes numerous important plant pathogenic species and species complexes that infect a wide variety of hosts. Its taxonomy is particularly complex because species' phenotypes and genotypes are difficult to differentiate. Two notable complexes, C. acutatum and C. gloeosporioides , are known for infecting temperate fruit crops worldwide. Even species within these complexes vary in traits such as tissue specificity, aggressiveness, geographic distribution, and fungicide sensitivity. With few effective chemicals available to control these pathogens, and the persistent threat of fungicide resistance, there is a need for greater understanding of this destructive genus and the methods that can be used for disease management. This review summarizes current research on diseases caused by Colletotrichum spp. on major fruit crops in the United States, focusing on the taxonomy of species involved, disease management strategies, and future management outlook.