Baseline sensitivity and efficacy of fluopyram against Botrytis cinerea from table grape in Italy
Succinate dehydrogenase inhibitor (SDHI) fungicides constitute a relatively recent fungicide class registered for the treatment of grey mould on grapevine in Italy. The sensitivity profile to a novel compound fluopyram was established for a set of 203 Botrytis cinerea isolates collected from Sicilian vineyards within 2009–2012 prior its introduction into market. In addition, its performances were compared in in vitroand in vivo assays with other registered SDHI fungicide boscalid, to evaluate their frequency distributions EC50 values and cross-resistance patterns. Results of the article showed that EC50 values for fluopyram ranged from 0.05 to 1.98 µg mL−1. Although EC50 values of boscalid ranged from 0.01 to 89.52 µg mL−1, no cross-resistance relationship was observed between the two fungicides (r = 0.003; P = 0.964) within our B. cinerea population. On further confirming these data, boscalid failed in controlling grey mould infections when boscalid-resistant isolates were inoculated on grape berries whereas fluopyram exhibited a good efficacy against the same isolates. This study represents the first report on the baseline sensitivity to fluopyram within B. cinerea population from Sicilian table grape vineyards in Italy, and it clearly shows the lack of cross-resistance in vitro and in vivo between fluopyram and boscalid for the field pathogen isolates. These results provided useful information for managing of fungicide resistance suggesting that fluopyram could be a valid alternative to boscalid for the control of grey mould of table grape.
Reduced sensitivity of tomato early blight pathogen (Alternaria solani) isolates to protectant fungicides, and implication on disease control
The sensitivity of Alternaria solani isolates to the fungicides mancozeb and chlorothalonil was evaluated, to determine if inadequate disease management by these fungicides could be attributed to reduced sensitivity of A. solani isolates to these fungicides. The sensitivity of 60 isolates of A. solani was assessed using the inhibition of radial mycelial growth (RG) method, using fungicide concentrations of 0, 1.0, 10, 100, 500 and 1000 μg a.i ml−1 medium. EC50 was calculated for each isolate and fungicide combination. The EC50 values of different A. solani isolates to mancozeb ranged from 9.05 to 712.65 μg ml−1. EC50 values of different isolates to chlorothalonil ranged from 4.25 to 849.4 μg ml−1. The percentage of isolates with reduced sensitivity was 46.7 and 53.3% for mancozeb and chlorothalonil, respectively. Results of the in vivo tests demonstrated decline in disease control by the two fungicides with the reduced-sensitivity isolates compared to the sensitive ones.
Pathotypes and metalaxyl sensitivity of Phytophthora sojae and their distribution in Heilongjiang, China 2011–2015
A total of 395 single-zoospore isolates of Phytophthora sojae that were obtained from 467 soybean fields in Heilongjiang, China from 2011 to 2015 were identified for pathotypes using differential soybean cultivars with Rps1a, Rps1b, Rps1c, Rps1d, Rps1k, Rps2, Rps3a, Rps3b, Rps3c, Rps4,Rps5, Rps6, Rps7, and Rps8 resistance genes. The results showed that P. sojae was widespread in Heilongjiang, but not evenly distributed. A heavy infestation of P. sojae in eastern Heilongjiang coincided with the serious diseases caused by this pathogen in that region. Among 135 pathotypes were identified, 20 isolates matched races of P. sojae based on published race definitions. To our knowledge, this is the first report of races 2, 8, 23, 25, 26, 29, 33, 39, 42, 43, and 48 in Heilongjiang. Race 1, previously considered as the dominant race in Heilongjiang, only comprised 1.52 % of the isolates in the present study. Virulence frequencies of 395 isolates to 14 Rps genes ranged from 17.85 to 82.41 %. Less than 30 % of the isolates were virulent on cultivars containingRps genes 1k, 1c, or 3a, which indicated that these Rps genes were more effective than other genes in Heilongjiang. All isolates could defeat more than two Rps genes. Ninety-six percent of the isolates were virulent against more than four Rps genes, which indicated that multi-virulence isolates existed in Heilongjiang. All 223 tested isolates were sensitive to metalaxyl, but EC50 for this fungicide against the pathogen increased 18-fold in the last 20 years. The results of the present study suggest that incorporating Rps genes 1c, 1k, and 3a into soybean cultivars and the use of metalaxyl-coated seeds should provide integrated approach to manage Phytophthora root and stem rot of soybean in Heilongjiang, China.
Genome-wide association study identifies novel candidate genes for aggressiveness, deoxynivalenol production and azole sensitivity in natural field populations of Fusarium graminearum
Genome wide association studies (GWAS) can identify novel genomic regions and genes that affect quantitative traits. Fusarium head blight is a destructive disease caused by Fusarium graminearum that exhibits several quantitative traits, including aggressiveness, mycotoxin production and fungicide resistance. Restriction site associated DNA sequencing (RADseq) was performed for 220 isolates of F. graminearum. 119 isolates were phenotyped for aggressiveness and deoxynivalenol (DON) production under natural field conditions across four environments. EC50 values for propiconazole resistance were calculated for 220 strains in vitro. Approximately 29,000 single nucleotide polymorphism markers were associated to each trait, resulting in 50, 29, and 74 quantitative trait nucleotides (QTNs) that were significantly associated to aggressiveness, DON production, and propiconazole sensitivity, respectively. Approximately 41% of these QTNs caused non-synonymous substitutions in predicted exons while the remainder were synonymous substitutions or located in intergenic regions. Three QTNs associated with propiconazole sensitivity were significant after Bonferroni correction. These QTNs were located in genes not previously associated with azole sensitivity. The majority of the detected QTNs were located in genes with predicted regulatory functions, suggesting that nucleotide variation in regulatory genes plays a major role in the corresponding quantitative trait variation.
The reasons of fungicide resistance of plant ppathogenic fungi
Crop protection against plant pathogenic fungi is one of the basics ensuring high yields. Unfortunately, resistance to fungicides has the tendency to occur more frequently. The causes of the decline of active substances protective effect are usually mutations in genes of fungicide target proteins. The other factors of increasing resistance level include overexpression of target protein, synthesis of alternative enzymes replacing functions of inhibited enzymes or removal of fungicides from cells by ABC and MFS protein transporters. Currently, due to the increased incidence of this phenomenon is important to use fungicides according to practices preventing the formation of fungi resistance.