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In a number of pathosystems involving the powdery mildews (Erysiphales), plant stress is associated with decreased disease susceptibility and is detrimental to pathogen growth and reproduction. However, in strawberry, anecdotal observations associate severe powdery mildew ( Podosphaera aphanis ) with water stress. In a 2017 survey of 42 strawberry growers in Norway and California, 40 growers agreed with a statement that water-stressed strawberry plants were more susceptible to powdery mildew compared with nonstressed plants. In repeated in vitro and in vivo experiments, we found that water stress was consistently and significantly unfavorable to conidial germination, infection, and increases in disease severity. Deleterious effects on the pathogen were observed from both preinoculation and postinoculation water stress in the host. Soil moisture content in the range from 0 to 50% was correlated ( R 2 fits the norm for biotrophic powdery mildews and hosts under stress. Mild water stress, compared with a state of optimal hydration, is likely to decrease rather than increase susceptibility of strawberry to P. aphanis fits the norm for biotrophic powdery mildews and hosts under stress. Mild water stress, compared with a state of optimal hydration, is likely to decrease rather than increase susceptibility of strawberry to P. aphanis could easily be mistakenly attributed to water stress, which we observed as having a nearly identical leaf curling symptom in strawberry.P. aphanis could easily be mistakenly attributed to water stress, which we observed as having a nearly identical leaf curling symptom in strawberry.

During the 2019-2020 Florida strawberry season (October to April), a strawberry ( Fragaria × ananassa ) fruit rot was observed in two fields (Plant City and Wimauma, FL) with up to 5% incidence on short-day cultivars Sensation TM Florida127, and Florida Brilliance. Symptoms on pink and ripe fruit consisted of softening, discoloration, watery rot with white fuzzy mycelium, and initial sclerotium formation. Diseased tissue was placed on General Isolation (GI) medium (Amiri et al. 2018) and incubated at 25°C under a 12-h photoperiod. A fungus producing spreading cottony white colonies with dark sclerotia near the outer edges of the plates was consistently isolated. One isolate from each cultivar field (20-51 and 20-55) was selected for identification and pathogenicity tests. Apothecial production was induced following the protocol of Li and Rollins (2009), and apothecia (n=30) had an average diameter of 4.5 (3.5 to 7.2) mm. Sclerotia were 3.6 (2.5 to 6.2) mm by 4.5 (3.1 to 5.9) mm (n=30) in size. Dimensions of asci were 130.2 (115.1 to 160.5) μm by 8.5 (6.2 to 13.1) μm (n=30), and those of ascospores were 12.2 (10.8 to 14.6) μm by 6.8 (5.7 to 8.1) μm (n=30). Based on these morphological features, the pathogen was tentatively identified as Sclerotinia sclerotiorum (Lib.) de Bary (Maas 1998). DNA was extracted from the same two isolates using the FastDNA kit (MP Biomedicals, Solon, OH), and the ribosomal internal transcribed spacer (ITS) region was amplified using the primers ITS1 and ITS4 (White et al. 1990). Sequences were deposited in GenBank (accession nos. MT378215 and MT378216). BLASTn searches revealed that isolates 20-51 and 20-55 were 99.62% identical (526 / 528 bp) to S. sclerotiorum CBS 499.50 (MH856725.1). Immature pink fruit of Sensation TM 'Florida127' were harvested, surface disinfested in bleach solution (0.08% NaClO) for 90 sec, rinsed twice with deionized water, then placed into styrofoam egg cartons inside clean plastic boxes (30x24x7 cm) containing 150 ml of sterile deionized water to maintain moisture, and kept at 25°C with a 12-h photoperiod. Ascospores and sclerotia were used for inoculation tests with three repetitions in an egg carton containing 12 fruit each per isolate and inoculation method. The experiment was repeated once. Fruit were inoculated by placing 20 μl of a 1 × 10 6 ascospores/mL suspension or a single sclerotium on the upper half of the fruit. Controls were included, by placing 20 μl of sterile DI water or fruit with no sclerotia. Evaluations were done 6, 10, and 15 days after inoculation (DAI). Control fruit remained healthy, while inoculated fruit developed symptoms of softening and discoloration. For ascospore inoculation, disease incidence was 55 (± 5) and 78% (± 4), for 6 and 15 DAI, respectively, whereas for sclerotia inoculation incidence was 100% 6 DAI. Morphologically identical fungi to the original isolates were re-isolated from the diseased fruit. No other fruit decay fungi were observed. S. sclerotiorum has been previously reported causing strawberry fruit rot in Washington state in the United States, England, Israel, and Scotland (Alcorn 1966; Maas 1998; McLean 1957). It has also been listed in the indices of plant diseases from Florida, North Carolina, and California as causing crown rot (Farr and Rossman 2020). To our knowledge, this is the first report of S. sclerotiorum causing strawberry fruit rot in Florida. The pathogen is an aggressive necrotroph with prolonged survival and affects several vegetable crops grown in Florida (Paret et al. 2018). Because only the strawberry beds are fumigated, sclerotia remaining in the alleys could serve as inoculum sources. Currently, the disease is rare and of minor significance to strawberry production. However, efforts should be implemented to monitor its occurrence and spread.

Strawberry ( Fragaria x ananassa ) is an important crop in the U.S., and Florida is the second major producer in the country. In January 2020, an unknown fruit rot was observed in two strawberry fields in Dover (seedling selection) and Plant City (cultivar Florida127), Florida. Disease incidence varied from less than 1% in one field to up to 15% in the second field during some harvests where over-ripe fruit were present. Affected fruit had a water-soaked soft rot with a sour smell, and sometimes with white mycelium on the fruit surface. Direct isolation was performed from symptomatic fruit from each area by touching the surface of a lesion with a sterile needle and streaking the fungus over general isolation medium (Amiri et al. 2018). The fungus was incubated at 25°C and 12-h photoperiod for five days. Four single-spore isolates (20-46 and 20-47 from Plant City; 20-49 and 20-50 from Dover) obtained from different colonies were grown on potato dextrose agar (PDA). Colonies were white to cream, flat, with a powdery surface, and had a characteristic sour odor. Hyphae were hyaline, septate, growing in a dichotomous pattern and often disarticulating into arthroconidia, which were unicellular, spherical to cylindrical, measuring 4.8 to 9.5 × 3.5 to 5.6 µm (n = 50). Based on the morphological characteristics, the fungus was identified as Geotrichum candidum (De Hoog et al. 1986). To confirm the identity of the isolates, the ribosomal internal transcribed spacer (ITS-rDNA) and the translation elongation factor 1-alpha (TEF1-α) gene regions were amplified and sequenced using the primers ITS1/ITS4 (White et al. 1990), and EF1-728F/EF1-1567R (Carbone and Kohn 1999), respectively. Consensus sequences were deposited in the GenBank (accession numbers MT353975 to MT353978 for ITS-rDNA, and MT346367 to MT346370 for TEF1-α). The BLASTn analysis revealed 99% identity with reference sequences of G. candidum for ITS-rDNA (KU373122) and TEF1-α (MK397513). Phylogenetic analysis, including ITS sequences of G. candidum and other spp., obtained from GenBank, was performed using maximum likelihood and Bayesian inference methods, implemented in MEGA-X and MrBayes, respectively. The isolates were grouped within the G. candidum clade. The pathogenicity of the fungus (isolate 20-46) was evaluated in ripe and green strawberry fruit (cultivar Florida127). Non-wounded and superficially wounded (with a sterilized needle) fruit were inoculated with 20 µl of a spore suspension (1 × 10 7 spore/ml), prepared by washing the surface of a 5-day-old colony on PDA, with sterile deionized water (SDW) plus 0.01% (v/v) Tween 20. Wounded and non-wounded control fruit were treated with SDW. Fruit were maintained in moist containers at 25°C. Each treatment consisted of 12 fruit (three replicates, each containing four fruit) and was evaluated daily for 10 days. Symptoms of sour rot were visible as soon as 48 hr after inoculation, but only on ripe (100% incidence) and green (58% incidence) wounded fruit. Symptoms progressed to an intense water-soaking with the presence of a typical white mycelium on the surface. Control fruit remained symptomless. The fungus was successfully recovered from symptomatic fruit, fulfilling Koch's postulates. Although strawberry fruit rots caused by G. candidum have already been reported in Pakistan and China (Hussain et al. 2016; Ma et al. 2018), this is the first report of this species causing sour rot on strawberry in the U.S. The disease may be a minor problem on damaged or over-ripe fruit, but further studies might be needed to determine its importance, distribution, and potential strategies for control.

Postbloom fruit drop (PFD) of citrus is caused by the Colletotrichum acutatum and C. gloeosporioides species complexes. The disease is important when frequent rainfall occurs during the flowering period of citrus trees. In Brazil, until 2012, PFD was mainly controlled by preventive applications of the methyl-benzimidazole carbamate (MBC) carbendazim and demethylation-inhibitor (DMI) fungicides such as difenoconazole. Since then, mixtures containing the DMI tebuconazole and the quinone-outside inhibitor (QoI) trifloxystrobin have been commonly used. Fungicides are often applied preventively, sometimes even when conditions are not conducive for PFD development. Excessive fungicide applications may favor the selection of resistant populations of Colletotrichum spp. In this study, we assessed the fungicide sensitivity of C. acutatum isolates collected during the two distinct periods of PFD management in Brazil: before and after the trifloxystrobin and tebuconazole mixture became widely employed. The sensitivity of 254 C. acutatum isolates to carbendazim and difenoconazole and of 164 isolates to tebuconazole and trifloxystrobin was assessed. Mycelial growth inhibition of these isolates was evaluated for all the fungicides using either serial dilution of fungicide rates or the spiral gradient dilution method. In addition, inhibition of conidial germination was also assessed for trifloxystrobin. Analysis of partial β-tub , cytb , and cyp51b gene sequences did not reveal any mutations related to resistance to MBCs, QoIs, and DMIs, respectively. In mycelial growth assays, mean EC 50 values were 0.14, 0.11, and 0.21 μg/ml for difenoconazole, tebuconazole, and trifloxystrobin, respectively. The conidial germination inhibition by trifloxystrobin was similar among the tested isolates, and the mean EC 50 value was 0.002 μg/ml. All isolates had similar mean mycelial growth inhibition for carbendazim, regardless of the fungicide concentrations. Therefore, based on similar EC 50 values and molecular analyses, no shift in the sensitivity of isolates has been observed to the fungicides commonly used in different citrus-producing areas in Brazil.

Succinate dehydrogenase inhibitors (SDHIs) are the fungicides most commonly used to control Botrytis fruit rot on commercial strawberry in Florida. The medium-to-high risk of selection of resistance in the causal agent Botrytis cinerea is a threat to the efficacy of this fungicide group. In this study, we characterized the sensitivity of B. cinerea to the SDHI isofetamid, evaluated the SdhB gene mutation associated with resistance, and monitored resistance frequencies to five SDHI fungicides for two consecutive seasons. EC 50 values of 70 isolates were obtained using the spiral gradient dilution (SGD) method and averaged 0.098 µg/ml of isofetamid. EC 50 averages of 3.04 and >500.00 µg/ml were obtained for isolates with the N230I and P225F mutations indicating moderate and high resistance to isofetamid, respectively. A total of 565 B. cinerea isolates collected during 2015-2016 and 2016-2017 seasons from strawberry nurseries and Florida production fields were evaluated using conidial germination assays. Results for the first season showed resistance frequencies of 95, 33, 21, 25, and 0% to boscalid, penthiopyrad, fluopyram, benzovindiflupyr, and isofetamid, respectively. The respective resistance frequencies for the following season were 91, 95, 44, 27, and 1.3%. Only three isolates were found to be moderately resistant to isofetamid during the second season, and the mutation N230I was identified after sequence analysis. These isolates were confirmed to be resistant to isofetamid in fruit assays with disease incidence of 55.6 to 77.0%; however, the conidial production of the isolates was inhibited by an average of 83.9%. In general, isofetamid efficacy was higher than the other evaluated SDHIs, but a slight increase in resistance frequencies was observed in our study.

Background: Ethanedinitrile (EDN) has shown promising efficacy against weeds, plant-parasitic nematodes and soil-borne pathogens. Field experiments were conducted for three strawberry (Fragaria× ananassa D.) seasons in Balm and Dover, FL, USA to evaluate the control efficacy of EDN applied through drip tape on various weed species and the fungus Macrophomina phaseolina, the causal agent of charcoal rot of strawberry., Results: Results revealed that 224, 336, 448 or 560 kg ha -1 EDN, and 104 kg ha -1 1,3-dichloropropene (1,3-D) + 176 kg ha -1 chloropicrin (Pic) applied through drip tapes under totally impermeable film were safe for strawberry production, with no adverse effect on strawberry growth and yield. EDN rates at 224, 336, 448 and 560 kg ha -1 were highly efficacious and equally effective in reducing purple nutsedge (Cyperus rotundus L.) in two of three growing seasons. Compared with the efficacy on purple nutsedge, the evaluated EDN rates were generally less effective on various broadleaf and grass weeds emerging on the bare ground and planting holes, but at 560 kg ha -1 consistently exhibited similar levels of control as 1,3-D + Pic. For M. phaseolina, the evaluated EDN rates were more efficacious than 1,3-D + Pic and significantly reduced inoculum buried in different bed locations in plastic-mulched beds., Conclusion: EDN has potential to be an efficacious tool for soil disinfestation and weed control in plasticulture strawberry production. © 2019 Society of Chemical Industry., (© 2019 Society of Chemical Industry.)

Anthracnose fruit rot and leaf blight caused by Colletotrichum species are important diseases of pomegranate in the southeastern United States. In this study, 26 isolates from pomegranate were identified based on pathological and molecular characterization. Isolates were identified to species based on multilocus sequence analysis with the internal transcribed spacer region, glyceraldehyde-3-phosphate dehydrogenase, β-tubulin, and chitin synthase genomic genes. Pomegranate isolates grouped within the C. acutatum and C. gloeosporioides species complexes, with more than 73% belonging to the latter group. Three species were identified within the C. acutatum species complex ( C. nymphaeae [ n = 5], C. fioriniae [ n = 1], and C. simmondsii [ n = 1]), and three other species were identified within the C. gloeosporioides species complex ( C. theobromicola [ n = 11], C. siamense [ n = 6], and C. gloeosporioides [ n = 2]). Inoculations of pomegranate fruit showed that isolates from the C. acutatum species complex were more aggressive than isolates from the C. gloeosporioides species complex. Interestingly, opposite results were observed when leaves of rooted pomegranate cuttings were inoculated. In addition, Colletotrichum isolates from pomegranate, strawberry, blueberry, mango, and citrus were cross-pathogenic when inoculated to fruit. This is the first study identifying six different species of Colletotrichum causing pomegranate leaf blight and fruit anthracnose in the southeastern United States and the potential cross-pathogenic capability of pomegranate isolates to other commercially important crops.

Botrytis fruit rot (BFR) is a major disease that affects strawberry production in Florida and worldwide. BFR management relies on frequent fungicide applications. A meta-analysis was conducted on the outcomes from nine field trials to evaluate the efficacy and profitability of conventional and biological fungicides compared with a nontreated control (NTC). All trials were conducted in Florida between the 2005/06 and 2016/17 growing seasons. Fungicide treatments were applied weekly, and plots were harvested twice a week for yield and BFR incidence quantification. Treatments were grouped into four categories: NTC, multisite only (Thiram), Standard (captan alternated with fludioxonil + cyprodinil), and Bacillus . Following primary analyses, a random effects network meta-analytical model was fitted to estimate the mean yield and BFR incidence responses for each treatment group and to compare means between pairs of groups. The Thiram and the Standard treatment groups increased yield by 378.8 and 502.2 kg/ha/week, respectively, compared with the NTC. The yield difference between Bacillus and NTC was not statistically significant. Besides increasing yield, Thiram and Standard also reduced BFR incidence by approximately 10% compared with the NTC. The mean yield responses and among-study variability from the meta-analysis were used to estimate the probability of a given yield response in a new future trial. The Standard and Thiram treatment groups showed higher estimated probabilities of increasing yield and resulting in a profitable return on application investments than the Bacillus group of treatments. The results from this study provide growers with information that will aid their decision-making process regarding BFR management.

Glomerella leaf spot (GLS) and bitter rot (BR) on apples are often caused by Colletotrichum acutatum in Paraná State, Brazil. GLS control is difficult because of its rapid development, with an incubation period of only 2 days under favorable conditions. Therefore, producers use successive fungicide applications every season; however, failure to control GLS has been commonly reported. The objectives of this study were to determine the sensitivity of isolates of the C. acutatum species complex obtained from apple orchards in Brazil to mancozeb, thiophanate-methyl, and azoxystrobin fungicides. Isolates from the different parts of the plant (leaves, flowers, buds, and twigs) and cultivars (Gala and Eva) showed different levels of sensitivity to mancozeb, thiophanate-methyl, and azoxystrobin. For mancozeb, the frequencies of isolates were 25% highly resistant, 50% low-resistance, and 25% sensitive. For thiophanate-methyl, the frequencies of isolates were 72.2% highly resistant, 11.1% resistant, and 16.7% moderately resistant. For azoxystrobin, the frequencies of isolates were 11.1% highly resistant, 5.6% resistant, and 83.3% sensitive. Interestingly, no mutations in the β-tubulin and cytochrome b genes were observed in any of the isolates resistant to thiophanate-methyl and azoxystrobin fungicides.

Macrophomina phaseolina , the causal agent of charcoal rot, affects strawberry crowns, inducing plant collapse. The fungus survives in the soil through the production of microsclerotia and is usually controlled by preplant fumigation of soil. However, in the 2016 to 2017 Florida strawberry season, even after soil fumigation, about 30% plant mortality still occurred in plastic-covered beds that were used for a second season and where crop residue (mainly old strawberry crowns) was disposed of between beds. Therefore, this study was conducted to determine if M. phaseolina can survive on strawberry debris over summer in Florida and if so, verify whether strawberry debris might act as a source of inoculum for new transplants. Crowns from the previous season were collected from commercial farms where charcoal rot had been reported, and M. phaseolina was recovered from all samples. In a research field, infected crowns were buried in the soil at different depths and retrieved every 2 weeks during the summer. After 8 weeks, M. phaseolina could be recovered at all depths. Moreover, inoculation of strawberry plants by drenching the soil, dipping roots, or spraying leaves with a M. phaseolina microsclerotial suspension from pure cultures or infected crowns produced symptoms with differences in incubation periods depending on cultivar susceptibility. Furthermore, infected crowns disposed of in the aisles between beds or buried next to new transplants of cultivars Strawberry Festival, Florida Beauty, and Winterstar induced charcoal rot, with the level of aggressiveness depending on the cultivar susceptibility and inoculum placement in the field.

Postbloom fruit drop (PFD) of citrus, caused by Colletotrichum acutatum sensu lato and C. gloeosporioides sensu lato, is an important disease in the humid tropics of the American continent. PFD mainly affects flowers, on which typical symptoms are characterized by orange-brown lesions with presence of acervuli. The disease has a sporadic occurrence, but preventative fungicide sprays are applied every season. The objective of this study was to evaluate the effectiveness of a fungicide spray strategy for PFD based on a predictive model of C. acutatum conidium germination linked to weather conditions. Fungicide sprays were performed when the model predicted pre-established thresholds of 10, 15, 20, and 25% of germinated spores (T10, T15, T20, and T25, respectively). Five experiments were conducted in two different seasons in the state of São Paulo, Brazil. PFD control efficacy of the threshold-based treatments was compared with a nontreated control and to a calendar-based spray system. Additionally, an economic analysis was performed to assess the gross income revenues of the fungicide spraying strategies. Disease control in plots treated at T10, T15, and T20 was as effective as the calendar-based strategy. The number of fungicide applications was reduced by 33 to 71% when sprays were applied at T15 and T20, and gross income increased or was comparable to that of the other treatments. Therefore, using a conidium germination model with a threshold of 15 or 20% is recommended as a spraying strategy for PFD management in Brazil.

Strawberry anthracnose fruit rot and root necrosis, caused by Colletotrichum acutatum , are primary limiting factors in fruit production fields in the United States. Recent research focusing on the phenotypic and genetic characteristics of this species has shed light on the diversity of the C. acutatum species complex. In this study, we performed multilocus sequence analysis of four genetic loci to characterize 217 C. acutatum isolates collected over a 23-year period from symptomatic plant tissues of strawberry from six different states. The results revealed two Colletotrichum spp. ( C. nymphaeae and C. fioriniae ), with 97.7% of the isolate collection (212 of 217) belonging to C. nymphaeae as a dominant clonal linage, regardless of the isolation source. No correlation between species groups and geographical origins of the isolates was observed. Further sequence comparison between historical and contemporary isolates showed the same populations being widely distributed throughout the strawberry nurseries and production fields in the United States and Canada. Subsequently, a subset of 12 isolates representing different quinone-outside inhibitor fungicide resistance profiles from root or fruit tissue of strawberry was selected for comparison of pathogenicity on strawberry. In this test, isolates of different resistance groups or different isolation sources exhibited a similar degree of aggressiveness and caused indistinguishable symptoms on strawberry crowns ( P = 0.9555 and 0.7873, respectively) and fruit ( P = 0.1638 and 0.1141, respectively), although a significant difference among individual isolates was observed in detached-fruit assays ( P = 0.0123). Separate pathogenicity tests using isolates of the two species revealed C. nymphaeae being more aggressive than C. fioriniae in infecting strawberry roots and crowns ( P = 0.0073). Therefore, given the occurrence and pathogenicity of C. nymphaeae , this species is likely the sole cause responsible for strawberry anthracnose in the United States.

Botrytis fruit rot (BFR), caused by the necrotrophic fungus Botrytis cinerea, is the most important disease of strawberry and is mainly controlled by applications of fungicides from multiple chemical groups. To develop more effective and sustainable BFR management programs, field trials were conducted to evaluate the efficacy of fluopyram and penthiopyrad, two newly registered succinate dehydrogenase inhibitors (SDHIs), rotated or tank mixed with the multisites thiram and captan or the single-sites fludioxonil and fenhexamid. The treatments were applied at two different strawberry fields during the 2013-14 and 2014-15 seasons. Overall, tank mixtures of fluopyram and penthiopyrad increased yield and reduced BFR better than rotations with the same fungicides. The multisite thiram tank mixed with fluopyram reduced BFR incidence by 63 to 86% versus 56 to 84% when the two fungicides were rotated. Thiram tank mixed with penthiopyrad reduced BFR incidence by 55 to 72% versus 42 to 66% when rotated. Captan rotated or tank mixed with fluopyram had a positive effect on yield and BFR incidence, whereas the combination of captan with penthiopyrad had negative impacts. Similarly, the single-site fenhexamid had significant positive impacts when rotated or tank mixed with fluopyram but resulted in poor BFR control when combined with penthiopyrad. The rotation of fludioxonil with both SDHIs had a significant positive effect, although its combination with fluopyram was more effective. The multirotation consisting of both SDHIs and different multi- and single-site fungicides did not provide a greater efficacy than the dual rotation or tank-mixture programs. Our findings suggest more scrutiny is needed when recommending tank-mixture or rotation partners for new fungicides to ensure compatibility and enhanced BFR management. Future recommendations should emphasize the importance of such selections at an early stage for delaying fungicide resistance development and extending the lifespan of at-risk fungicides.

Glomerella leaf spot (GLS) is an apple disease that concerns growers due to the increases in severity over the years and the difficulties in control. Species within the Colletotrichum acutatum and C. gloeosporioides species complexes cause GLS, but the proportion of species within each complex in Brazilian apple orchards is not known. The objectives of this study were to identify isolates of Colletotrichum causing GLS on apple orchards in the main Brazilian producing regions to the species level. Two hundred and seven isolates were obtained in orchards in São Paulo (SP), Parana (PR), Santa Catarina (SC), and Rio Grande do Sul (RS) states. Genomic DNA was extracted, and the ITS, GAPDH, CHS-1, and TUB2 genes were amplified and sequenced. The phylogenetic trees were generated using a concatenated alignment. One hundred and fourteen isolates were identified as belonging to the C. acutatum species complex (Cac) and 93 to the C. gloeosporioides species complex (Cgc). Five phylogenetic species were identified: C. melonis (1.9%), C. nymphaeae (47.4%), C. paranaense (2.4%), C. limetticola (3.4%), and C. fructicola (44.9%). In SC, Cgc predominates, but in the states of SP, PR, and RS, Cac was predominant. This is the first report of C. limetticola from apple.

Field validation of a disease-warning system for strawberry anthracnose fruit rot (AFR), caused by Colletotrichum acutatum sensu lato, that was originally developed for use in Florida was conducted in Iowa from 2012 to 2014. Day-neutral strawberry (cv. Tristar) was artificially inoculated with the pathogen at the start of the fruit maturation period. A factorial combination in replicated trials of two spray timing methods (the Florida warning system and prescheduled, calendar-based timing) and two fungicides (captan and pyraclostrobin) was compared, along with a nonsprayed control. The calendar-based and warning system-based treatments provided statistically equivalent control of AFR incidence compared with the nonsprayed control, and the warning system treatments required an average of 1.7 fewer fungicide sprays annually than the calendar-based treatments. Further analysis of the field data suggested that the warning system might underestimate AFR risk under high disease pressure; in these circumstances, a lower action threshold value may need to be adopted. Overall, these results indicated that the Florida warning system can be valuable for helping Midwest strawberry growers control AFR with less reliance on fungicide sprays, but it may require modification to account for periods of high inoculum pressure, subject to results of further field trials.

Although strawberry is an economically important fruit crop worldwide, production of strawberry is limited by its susceptibility to a wide range of pathogens and the lack of major commercial cultivars with high levels of resistance to multiple pathogens. The objective of this study is to ectopically express the Arabidopsis thaliana NPR1 gene (AtNPR1) in the diploid strawberry Fragaria vesca L. and to test transgenic plants for disease resistance. AtNPR1 is a key positive regulator of the long-lasting broad-spectrum resistance known as systemic acquired resistance (SAR) and has been shown to confer resistance to a number of pathogens when overexpressed in Arabidopsis or ectopically expressed in several crop species. We show that ectopic expression of AtNPR1 in strawberry increases resistance to anthracnose, powdery mildew, and angular leaf spot, which are caused by different fungal or bacterial pathogens. The increased resistance is related to the relative expression levels of AtNPR1 in the transgenic plants. In contrast to Arabidopsis plants overexpressing AtNPR1, which grow normally and do not constitutively express defense genes, the strawberry transgenic plants are shorter than non-transformed controls, and most of them fail to produce runners and fruits. Consistently, most of the transgenic lines constitutively express the defense gene FvPR5, suggesting that the SAR activation mechanisms in strawberry and Arabidopsis are different. Nevertheless, our results indicate that overexpression of AtNPR1 holds the potential for generation of broad-spectrum disease resistance in strawberry.