These data are concerning as they indicate that the highly resistant isolates have already developed cross-resistance between boscalid and penthiopyrad, despite penthiopyrad not yet having regular use in Michigan. To our knowledge, this is the first report of resistance to SDHI fungicides in populations of A. In this study, all of the isolates that were highly resistant to both boscalid and penthiopyrad were found to contain the H133R mutation in SdhD, which correlated with the strongest resistance phenotype. Because the majority of the identified mutations occur near the 3' end of each subunit, this region was amplified and sequenced using the following primer sets: SdhB (5'-TACTGGTGGAACCAGGAGGAGTA-3' and 5'-CATACCACTCTAGGTGAAG-3'), SdhC (5'-CCAAATCACCTGGTACGCCTCG-3' and 5'-TCATCCGAGGAAGGTGTAGTAAAGGCTG-3'), and SdhD (5'-CCGACTCTATTCTCTGCGCCCT-3' and 5'-CTCGAAAGAGTAGAGGGCAAGACCCA-3'). Recently, two major mutations, H227R in SdhB and H133R in SdhD, have been identified in highly resistant A. None of the isolates tested were resistant to fluopyram. Of all isolates tested, 11% were highly resistant to both boscalid and penthiopyrad and 5% were moderately resistant to both fungicides, 21% were moderately resistant to penthiopyrad alone, and the remaining isolates (84 and 68% respectively) were sensitive to the two fungicides. solani isolate (AS11) from Bonners Ferry, ID, was used as a control in these experiments. An isolate was considered highly resistant if fungal growth relative to control plates exceeded 50%, moderately resistant if it was between 35 and 50%, and sensitive if it was less than 35% (2). Mycelial plugs (~5.5 mm) were transferred to amended and non-amended PDA plates that were incubated at 25☌ for 7 days. solani isolates were obtained and each was screened for sensitivity to the SDHI fungicides boscalid, penthiopyrad, and fluopyram, using a 50 ppm discriminatory dose based on EC 50 values previously determined (2). The identity of cultures was confirmed by colony and conidial morphology (3). solani conidia were transferred to potato dextrose agar (PDA) and incubated at 25☌ for 7 days. Plates were incubated at 25☌ overnight to allow conidia to germinate. solani isolates from leaves, small pieces of leaf tissue (5 × 5 mm) were excised from the center of lesions and transferred on to water agar. To investigate the occurrence of SDHI resistance in Michigan, potato leaves with early blight symptoms were collected from fields in Montcalm and Ionia counties, MI, in 2012. Unfortunately, recent studies have shown that SDHI resistance has increased dramatically over the past 2 years in A. The disease is commonly managed using succinate dehydrogenase inhibitor (SDHI) fungicides (1). If left uncontrolled, it can result in yield losses exceeding 20% and impact stored potatoes. The lesion start with small yellow sections on the leaf that starts to turn brown, and this is especially noticed in leaves that are close to the ground.
Early blight trial#
A successful trial is one that is strictly carried out according to this protocol and early blight is observed in the plots (>10% foliar infection in the worst treatment).Early blight of potato (Solanum tuberosum) is caused by Alternaria solani and occurs annually in Michigan. Early blight can cause severe damage to tomatoes and symptoms can be on any of the above ground parts of the plant including leaves, stem and fruits. Further assessments are encouraged but not considered for an EuroBlight rating.
The last assessment will be carried out 3 to 4 weeks after the last spray application. The time frame of the spray applications should be the same for all treatments. In York it was decided that a spray strategy with more than 1 fungicide is no longer allowed, even if this means that 1 fungicide is sprayed in a 7-day interval and the other in a 14-day interval. The EuroBlight Table to rate the efficacy of crop protection products has changed. Responsible authors: Bert Evenhuis (WUR), Peter Hartvig (AU), Hans Hausladen (TUM) Efficacy of fungicides for the control of early blight caused by Alternaria solani and Alternaria alternata.
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