Detection of resistance of Alternaria kikuchiana causing pear black spot to fungicides and baseline sensitivity of A.kikuchiana to boscalid

Black spot caused by Alternaria kikuchiana is one of the main diseases of pears in China. Decreased controlling efficacy of traditionally applied fungicides(carbendazim etc.) against the disease was reported recently in some regions. Resistance development of 252 isolates of A.kikuchiana collected from different regions of Zhejiang, Jiangsu and Anhui province to fungicides was investigated through the mycelial growth rate method. The results showed that the resistance frequency of A.kikuchiana population(n=252) to carbendazim(a benzimidazole fungicide) was 57.1% and all resistant isolates showed high-level resistance(HR). The resistance frequency to iprodione(a dicarboximide fungicide) was 46.8% and all resistant isolates showed low-level resistance(LR). The LR and moderate-level resistance(MR) frequency to difenoconazole(a sterol demethylation inhibitor fungicide) was 28.6% and 28.6%, respectively. The results indicated that A.kikuchiana had developed resistance to these traditionally applied fungicides in Zhejiang, Jiangsu and Anhui province. Further work was carried out to establish the baseline sensitivity of A.kikuchiana to boscalid, a succinate dehydrogenase inhibitor fungicide. The EC50 values of boscalid to the tested population(n=252) varied from 0.12 to 3.85 μg/mL(mean value 1.21±0.12 μg/mL) following a unimodal distribution, suggesting that boscalid could be used as a potential alternative fungicide to control pear black spot.