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Horticultural performance of eleven blackberry cultivars, including two primocane-fruiting cultivars, was evaluated over three years after fruiting began at the Musser Fruit Research Center in South Carolina, United States. Results showed differences in yield between cultivars for each year of the study. 'Natchez' had the highest cumulative yield after three years, followed by 'Navaho', 'Von', and 'Osage', whereas 'Prime-Ark® Traveler' produced significantly less than these four cultivars. Yield steadily declined for all cultivars over the three years, except for 'Osage', which remained consistent. 'Prime-Ark® Freedom' always had the largest fruit, although it had the greatest yield reduction after the second year. Multiple factors may explain yield decline for the majority of the cultivars studied, including freeze damage and tip dieback. Tip dieback was observed in 2016 in multiple cultivars, but dieback incidence was highest on 'Prime-Ark® Traveler'. The dieback was associated with an outbreak of broad mites and thrips in the experimental block and with secondary pathogens isolated from the decaying tissues primarily Fusarium spp. and Alternaria spp. Cultivar differences in susceptibility to Alternaria spp. were confirmed in laboratory studies. [ABSTRACT FROM AUTHOR]

Blackberry fruits symptomatic for gray mold were collected from three commercial blackberry fields in northwestern South Carolina. Single-spore isolates were generated and two distinct phenotypes were discovered in each location; one sporulated on PDA and one did not. One isolate of each phenotype and location (six isolates total) were selected for in depth molecular and morphological characterization. Glyceraldehyde-3-phosphate dehydrogenase (G3PDH), heat-shock protein 60 (HSP60) and DNA-dependent RNA polymerase subunit II (RPB2) coding sequence alignment revealed Botrytis cinerea as the sporulating phenotype and a new yet undescribed species as the non-sporulating phenotype. The new Botrytis sp., described herein as Botrytis caroliniana, was most closely related genetically to B. fabiopsis and B. galanthina, the causal agents of gray mold disease of broad bean and snowdrop, respectively. It produces smaller conidia than either B. fabiopsis or B. galanthina, and sequence analysis of genes encoding necrosis and ethylene-inducing proteins (NEPs) also indicated that the Botrytis isolates represent a separate and distinct species. The new species is pathogenic on blackberry fruits and broad bean leaves, which distinguishes it further from B. galanthina. The new species formed white to pale gray colonies with short, tufted aerial mycelium and produced black sclerotia on PDA at 20 C. To our knowledge this is only the third Botrytis species discovered to cause disease on blackberry in the United States. [ABSTRACT FROM AUTHOR]

Colletotrichum gloeosporioides, C. acutatum, and C. truncatum are causal agents of anthracnose disease of peach in South Carolina, but more recent investigations show that C. gloeosporioides is a species complex that has not yet been investigated among peach isolates. A total of 28 Colletotrichum spp. isolates associated with peach fruit anthracnose were collected in 2012 from Chesnee (10 isolates), McBee (10 isolates), Monetta (2 isolates), and Ridge Spring (6 isolates), South Carolina. Morphological characteristics indicated that all 28 isolates belonged to the C. gloeosporioides species complex. Phylogenetic analysis of the combined calmodulin (CAL), glyceraldehyde-3- phosphate dehydrogenase (GAPDH), and (3-tubulin (TUB2) gene sequences identified two species, C. siamense and C. fructicola. Cultural characteristics such as colony growth rate, shape and size of conidia, and appressoria from representative isolates of the two species largely matched previous descriptions for C. siamense and C. fructicola. Koch's postulates for C. siamense and C. fructicola were fulfilled, confirming pathogenicity of the two species on peach. A new, two-step multiplex PCR assay was developed to facilitate differentiation of the four known Colletotrichum spp. causing anthracnose of peach in South Carolina, including C. acutatum, C. truncatum, C. siamense, and C. fructicola. The first step distinguished C. acutatum from C. truncatum and the two members of the C. gloeosporioides species complex. The second assay distinguished C. siamense from C. fructicola isolates. [ABSTRACT FROM AUTHOR]

Chemical control of gray mold of strawberry caused by Botrytis ci-nerea is essential to prevent pre- and postharvest fruit decay. For more than 10 years, the anilinopyrimidine (AP) cyprodinil and the phe-nylpyrrole fludioxonil (Switch 62.5WG) have been available to commercial strawberry producers in the United States for gray mold control. Both active ingredients are site-specific inhibitors and, thus, prone to resistance development. In this study, 217 single-spore iso-lates of B. cinerea from 11 commercial strawberry fields in North and South Carolina were examined for sensitivity to both fungicides. Iso-lates that were sensitive (53%), moderately resistant (30%), or resistant (17%) to cyprodinil were identified based on germ tube inhibition at discriminatory doses of cyprodinil at 1 and 25 mg/liter at 10 of the 11 locations. None of the isolates was fludioxonil resistant. Phenotypes that were moderately resistant or resistant to cyprodinil were not associated with fitness penalties for mycelial growth rate, spore produc-tion, or osmotic sensitivity. Detached fruit assays demonstrated cross resistance between the two AP fungicides cyprodinil and pyrimethanil, and that isolates that were characterized in vitro as moderately resistant or resistant were equivalent in pathogenicity on fruit sprayed with pyrimethanil (currently the only AP registered in strawberry as a solo formulation). This suggests that the in vitro distinction of moderately resistant and resistant isolates is of little if any field relevance. The absence of cross-resistance with fludioxonil, iprodione, cycloheximide, and tolnaftate indicated that multidrug resistance in the form of multi-drug resistance phenotypes was unlikely to be involved in conferring resistance to APs in our isolates. Implications for resistance manage-ment and disease control are discussed. [ABSTRACT FROM AUTHOR]

Botrytis cinerea, the causal agent of gray mold disease, is one of the most important plant-pathogenic fungi affecting strawberry. During the last decade, control of gray mold disease in the southeastern United States has largely been dependent on captan and the use of at-risk fungicides with single-site modes of action, including a combination of the quinone outside inhibitor (Qol) fungicide pyraclostrobin and succinate dehydrogenase inhibitor (SDHI) fungicide boscalid formulated as Pristine 38WG. Reports about loss of efficacy of Pristine in experimental fields in North Carolina prompted us to collect and examine 216 single-spore isolates from 10 conventional fields and 1 organic field in North Carolina and South Carolina in early summer 2011. Sensitivity to pyraclostrobin or boscalid was determined using a conidial germination assay with previously published discriminatory doses. Pyraclostrobin- and pyraclostrobin+boscalid-resistant isolates were found in all conventional fields (with some populations revealing no sensitive isolates) and in the organic field. Among the isolates collected, 66.7% were resistant to pyraclostrobin and 61.5% were resistant to both pyraclostrobin and boscalid. No isolates were identified that were resistant to boscalid but sensitive to pyraclostrobin, indicating that dual resistance may have derived from a Qol-resistant population. The molecular basis of Qol and SDHI fungicide resistance was determined in a subset of isolates. Polymerase chain reaction-restriction fragment length polymorphism analysis of the partial cytochrome b (CYTB) gene showed that pyraclostrobin-resistant isolates possessed the G143A mutation known to confer high levels of Qol fungicide resistance in fungi. Boscalid-resistant isolates revealed point mutations at codon 272 leading to the substitution of histidine to arginine (H272R) or tyrosine (H272Y), affecting the third Fe-S cluster region of die iron-sulfur protein (SdhB) target of SDHIs. The results of the study show that resistance to Qol fungicides and dual resistance to Qol and SDHI fungicides is common in B. cinerea from strawberry fields in the Carolinas. Resistant strains were more frequent in locations heavily sprayed with Qol and SDHI fungicides. However, resistance to both fungicides was also found in the unsprayed, organic field, indicating that some resistant strains may have been introduced from the nursery. [ABSTRACT FROM AUTHOR]

Methyl benzimidazole carbamate (MBC) fungicides were once widely used for brown rot (Monilinia fructicola) control of peach (Prunus persica (L.) Batsch) in the southeastern US, but their use was substantially reduced and often eliminated due to widespread resistance. In this study, 233 M. fructicola isolates were collected from major peach production areas in Alabama, Georgia, and South Carolina, and sensitivity to thiophanate-methyl was examined. Isolates were also collected from one organic and two experimental peach orchards. A discriminatory dose of 1 μg/ml was used to distinguish sensitive (S) and moderately sensitive (S-LR) isolates from low resistant phenotypes, while 50 and 500 μg/ml thiophanate-methyl concentrations were used to determine high resistant (HR) phenotypes. Sequence analyses were performed to identify mutations in the β-tubulin target gene and detached fruit assays were performed to determine the efficacy of a commercial product against isolates representing each phenotype. Results indicated 55.7%, 63.5%, and 75.9% of isolates from Alabama, Georgia, and South Carolina, respectively, were S to thiophanate-methyl; 44.3%, 36.5%, and 21.4% were S-LR; no isolates were LR; and only 3 isolates (1.3%) from South Carolina were HR. No mutations in S or S-LR isolates were found, but HR isolates revealed the E198A mutation, an amino acid change of glutamic acid to alanine conferring high resistance. The high label rate of a commercial product containing thiophanate-methyl controlled brown rot caused by S and S-LR isolates in detached fruit studies but was ineffective against HR isolates. The combinations of thiophanate-methyl with azoxystrobin or isofetamid, when mixed together and applied in an experimental orchard 14 days preharvest, significantly reduced brown rot incidence on pre and postharvest commercially ripe fruit and efficacy was comparable to that of a grower standard fungicide. These results indicate that thiophanate-methyl may again be useful to peach growers in the southeastern US for brown rot and fungicide resistance management. [Display omitted] • Monilinia fructicola isolates from three US states were largely sensitive or moderately sensitive to thiophanate methyl • Isolates resistant to thiophanate methyl contained E198A mutation in beta tubulin • Label rates of thiophanate methyl controlled brown rot caused by sensitive and moderately sensitive isolates • Field trials revealed thiophanate methyl applied in mixtures during preharvest controls brown rot [ABSTRACT FROM AUTHOR]

Anthracnose fruit rot was observed in some late-season peach cultivars in South Carolina in the 2012 and 2013 production seasons as well as increased anthracnose leaf spot of blueberry in a commercial operation of the same state in 2012. Single-spore isolates of Colletotrichum siamense were either sensitive or resistant to both thiophanate-methyl and azoxystrobin with the concentration of the fungicide at which fungal development is inhibited by 50% of a 100 p,g/ml. Resistant isolates revealed the E198A mutation in (3-tubulin and the G143A mutation in cytochrome b. Nucleotide sequence analysis of the complete CYTB gene from genomic DNA of C. siamense isolates revealed an intronless genotype (Crl) and a genotype revealing two introns (CsII) at amino acid positions 131 and 164. Resistance to thiophanate-methyl or azoxystrobin was not found in isolates of C.fructicola collected from peach fruit. The CYTB gene of isolates of this species was of the C/II genotype or revealed a unique C/IIa genotype. Phylogenetic analysis of C. siamense isolates from different locations and different crops showed that the resistant isolates were genetically closer to each other than to sensitive isolates, suggesting that field resistance to thiophanate-methyl and azoxystrobin fungicides is derived from a common ancestor. [ABSTRACT FROM AUTHOR]

The fungicide resistance profiles to seven chemical classes of fungicides were investigated in 198 Botrytis cinerea isolates from five blackberry fields and 214 B. cinerea isolates from 10 strawberry fields of North and South Carolina. Populations of B. cinerea tended to have a single dominant, location-specific resistance profile that consisted of resistance to multiple fungicides in fields sprayed weekly with sitespecific fungicides. The most prevalent profile in blackberry fields consisted of resistance to thiophanate-methyl, pyraclostrobin, and boscalid. The most prevalent resistance profile found in conventional strawberry fields consisted of resistance to thiophanate-methyl, pyraclostrobin, boscalid, and cyprodinil. A statistical model revealed that multifungicide resistance patterns did not evolve randomly in populations from both crops. Instead, strains resistant to thiophanate-methyl were more likely to acquire resistance to pyraclostrobin, the resulting dual-resistant population was more likely to acquire resistance to boscalid, the resulting triple-resistant population was more likely to acquire resistance to cyprodinil, and the resulting quadruple-resistant population was more likely to acquire resistance to fenhexamid (strawberry population only) compared with random chance. Resistance to iprodione and fludioxonil evolved from a pool of strains with different fungicide resistance profiles. Resistance to thiophanate-methyl, pyraclostrobin, boscalid, and fenhexamid in blackberry isolates was, without exception, based on target gene mutations, including E198A and E198V in ß-tubulin, G143A in cytochrome b, H272Y and H272R in SdhB, and F412I in Erg27, respectively. A new genotype associated with fenhexamid resistance was found in one strain (i.e., Y408H and deletion of P298). Fungicide-resistant strains were present but rare in an unsprayed blackberry field, where some unique phenotypes, including low and medium resistance to fludioxonil, had emerged in the absence of fungicide pressure. The isolates resistant to fludioxonil had effective dose that inhibited 50% of mycelial growth values of 0.16 pg/ml (low resistance) and 0.32 and 0.38 pg/ml (medium resistance) and were also resistant to the anilinopyrimidine fungicide cyprodinil, indicating that this and similar phenotypes will eventually be selected by continued applications of the fludioxonil + cyprodinil premixture Switch. This study shows that multifungicide-resistant phenotypes are common in conventionally maintained strawberry and blackberry fields and that resistance to multiple fungicides evolved from stepwise accumulation of single resistances. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa causes bacterial leaf scorch in southern highbush ( Vaccinium corymbosum interspecific hybrids) and is also associated with a distinct disease phenotype in rabbiteye blueberry ( V. virgatum ) cultivars in the southeastern United States. Both X. fastidiosa subsp. fastidiosa and X. fastidiosa subsp. multiplex have been reported to cause problems in southern highbush blueberry, but so far only X. fastidiosa subsp. multiplex has been reported in rabbiteye cultivars in Louisiana. In this study, we report detection of X. fastidiosa in rabbiteye blueberry plants in association with symptoms of foliar reddening and shoot dieback. High throughput sequencing of an X. fastidiosa -positive plant sample and comparative analyses identified the strain in one of these plants as being X. fastidiosa subsp. fastidiosa . We briefly discuss the implications of these findings, which may spur research into blueberry as a potential inoculum source that could enable spread to other susceptible fruit crops in South Carolina., Competing Interests: The author(s) declare no conflict of interest.

Bacterial spot of peach, caused by Xanthomonas arboricola pv. pruni , causes yield loss every year in southeastern U.S. peach orchards. Management is mainly driven by season-long applications of copper-based products, site location, and choice of cultivar. Although tolerance to copper has not been reported in X . arboricola pv. pruni in the United States, adaptation of populations from frequent use is a concern. We collected X . arboricola pv. pruni from shoot cankers, leaves, and fruit of cultivar O'Henry over 2 years from three conventional farms and one organic farm in South Carolina, one orchard per farm. The four farms had been using copper extensively for years to control bacterial spot. X . arboricola pv. pruni was isolated from four canker types (bud canker, tip canker, nonconcentric canker, and concentric canker) in early spring (bud break), as well as from leaf and fruit tissues later in the season at the phenological stages of pit hardening and final swell. X . arboricola pv. pruni was most frequently isolated from cankers of the organic farm (24% of the cankers) and most isolates (45%) came from bud cankers. X . arboricola pv. pruni isolates were assessed for sensitivity to copper using minimal glucose yeast agar and nutrient agar amended with 38 μg/ml or 51 μg/ml of Cu 2+ . Two phenotypes of copper tolerance in X . arboricola pv. pruni were discovered: low copper tolerance (LCT; growth up to 38 μg/ml Cu 2+ ) and high copper tolerance (HCT; growth up to 51 μg/ml Cu 2+ ). A total of 26 (23 LCT and 3 HCT) out of 165 isolates in 2018 and 32 (20 LCT and 12 HCT) out of 133 isolates in 2019 were tolerant to copper. Peach leaves on potted trees were sprayed with copper rates typically applied at the stages of delayed dormancy (high rate; 2,397 μg/ml Cu 2+ ), shuck split (medium rate; 599 μg/ml Cu 2+ ), and during summer cover sprays (low rate; 120 μg/ml Cu 2+ ), and subsequently inoculated with sensitive, LCT, and HCT strains. Results indicated that the low and medium rates of copper reduced bacterial spot incidence caused by the sensitive strain but not by the LCT and HCT strains. This study confirms existence of X . arboricola pv. pruni tolerance to copper in commercial peach orchards in the southeastern United States, and suggests its contribution to bacterial spot development under current management practices.

A survey of fungal pathogens causing twig blight on commercial peach trees was conducted in South Carolina in the fall of 2016. Shoots with cankers, pycnidia, and dieback were collected from six locations around the state. Isolates obtained from these samples were identified as Botryosphaeria obtusa, Phomopsis amygdali, Leucostoma persoonii, and Cytospora sp., based on colony morphology, conidia size and shape, and ribosomal DNA sequence analysis. L. persoonii was the most prevalent species and was isolated in five of the six locations, followed by P. amygdali and B. obtusa. The sensitivity of representative isolates of B. obtusa, P. amygdali, and L. persoonii to fungicides of different FRAC codes was evaluated. All species tested were sensitive to thiophanate-methyl (FRAC 1) and pyraclostrobin and azoxystrobin (both FRAC 11), whereas all species were resistant to boscalid and fluopyram (both FRAC 7). P. amygdali and B. obtusa were sensitive to difenoconazole and propiconazole (both FRAC 3), whereas L. persoonii was moderately resistant. L. persoonii was the most virulent species based on expansion of mycelium in the cambium layer of 2-year-old, detached twig pieces. Bacterial spot (BS)-sensitive cultivar 'O'Henry' was most susceptible to B. obtusa compared with BS-sensitive 'Summerprince', brown rot (BR)-resistant 'Contender', and BR-sensitive 'Coronet' but was least susceptible to L. persoonii. Coronet was most susceptible to L. persoonii. There were no significant differences between susceptibility of the cultivars to P. amygdali. This study established that L. persoonii is currently the most frequent twig blight pathogen in South Carolina, perhaps owing to its superior fitness. Some fungicides were effective in controlling all twig blight pathogens and may therefore be useful for chemical management strategies. Our study also provides the first evidence that the genetic basis of resistance to BS and BR in peach trees is not necessarily linked to tolerance to wood pathogens.

Gray mold, caused by Botrytis spp., is among the most devastating diseases affecting strawberry worldwide. The great diversity present in the pathogen enhances its ability to survive and adapt in the field. In this study, we explored the genotypic and phenotypic diversity present in single strawberry flowers. In total, 192 isolates were collected from 19 flowers and four farms, and 9 to 12 isolates were collected from each flower. Forty-two haplotypes were found using microsatellite fragment analysis. Multiple haplotypes of two different Botrytis spp. (Botrytis cinerea and B. fragariae) were found in 12 flowers. In the remaining seven flowers, the single-spore isolates examined were of identical haplotypes. In three flowers, the two Botrytis spp. were found to coexist. Isolates were either sensitive (zero chemical class resistance) or resistant to one, two, three, four, or five chemical classes of fungicides. Resistance to multiple fungicides was commonly observed in both species but resistance to boscalid and penthiopyrad was only found in B. cinerea isolates. Resistance to cyprodinil was found in B. fragariae for the first time in the United States. Each haplotype was generally linked to a single resistance profile; however, a single resistance profile often was represented by multiple haplotypes. Isolates from the same flower of multiple haplotypes were largely identical in resistance profiles. This study is a first detailed investigation of genotypic diversity combined with phenotypic analysis of Botrytis spp. at the single-tissue level. It demonstrates that high genotypic and phenotypic diversity is present not only within fields but also in individual blossoms as well. This information is important for understanding the epidemiology of Botrytis and also has implications for fungicide resistance management, particularly related to resistance monitoring practices.

Peach skin streaking is a previously undescribed skin discoloration affecting red-blush peach cultivars in Georgia and South Carolina. Streaked peach fruit have been observed in the field close to harvest. The cause of streaking is still unknown but one hypothesis is that atmospheric pollutants may be involved. The goal of this study was to establish proof of concept that commonly found air pollutants can produce streaks on peach skin similar to those observed in commercial orchards and investigate the susceptibility of peach fruit during maturation. Common reactive byproducts of atmospheric pollutants, including sulfuric acid (H 2 SO 4 ), nitric acid (HNO 3 ), and hypochlorite acid (HCl), at concentrations up to 10 μg/ml did not produce streaking under field conditions when applied at week 3, 2, and 1 prior to commercial harvest. However, sodium hypochlorite (NaClO) in the form of Clorox solution and chlorine dioxide (ClO 2 ) at 100 μg/ml generated from the Aquamira water treatment solution produced streaking symptoms on detached peach fruit under controlled conditions and in the field. Peach fruit were most susceptible to streaking closest to harvest, suggesting that NaClO and ClO 2 interfere with pigment formation.

Blackberry fruits symptomatic for gray mold were collected from three commercial blackberry fields in northwestern South Carolina. Single-spore isolates were generated and two distinct phenotypes were discovered in each location; one sporulated on PDA and one did not. One isolate of each phenotype and location (six isolates total) were selected for in depth molecular and morphological characterization. Glyceraldehyde-3-phosphate dehydrogenase (G3PDH), heat-shock protein 60 (HSP60) and DNA-dependent RNA polymerase subunit II (RPB2) coding sequence alignment revealed Botrytis cinerea as the sporulating phenotype and a new yet undescribed species as the non-sporulating phenotype. The new Botrytis sp., described herein as Botrytis caroliniana, was most closely related genetically to B. fabiopsis and B. galanthina, the causal agents of gray mold disease of broad bean and snowdrop, respectively. It produces smaller conidia than either B. fabiopsis or B. galanthina, and sequence analysis of genes encoding necrosis and ethylene-inducing proteins (NEPs) also indicated that the Botrytis isolates represent a separate and distinct species. The new species is pathogenic on blackberry fruits and broad bean leaves, which distinguishes it further from B. galanthina. The new species formed white to pale gray colonies with short, tufted aerial mycelium and produced black sclerotia on PDA at 20 C. To our knowledge this is only the third Botrytis species discovered to cause disease on blackberry in the United States.