Monitoring and characterization of resistance development of strawberry Phomopsis leaf blight to fungicides
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Monitoring and characterization of resistance development of strawberry Phomopsis leaf blight to fungicides Haojie Shi & Huiming Wu & Chuanqing Zhang & Xin Shen
Accepted: 3 October 2012 / Published online: 12 October 2012 # KNPV 2012
Abstract From 2005 to 2009, a total of 479 singleconidial isolates of Phomopsis obscurans were collected from strawberry. The isolates were characterized for their resistance to benzimidazole fungicides, diethofencarb, and sterol demethylation inhibitors (DMIs). Low-level DMI resistant isolates (DMI-LR) and two types of benzimidazole-resistant (Ben R) isolates, Ben R1 (benzimidazole-resistant and diethofencarb -sensitive) and Ben R2 (benzimidazole-resistant and diethofencarb -resistant), were detected. Both Ben R and DMI-LR isolates exhibited comparable growth, sporulation, and pathogenicity with the sensitive isolates. No significant difference in growth at low temperature was observed between Ben R and benzimidazole-sensitive (Ben S) isolates. Ben R1 was caused by a point mutation from GAG to GTG at codon 198 in the β-tubulin gene in Ben S isolates, predicted to cause a change from glutamic acid to valine. Ben R2 was induced by a point mutation from TTC to TAC at codon 200 in the β-tubulin gene in Ben S isolates. Keywords Phomopsis obscurans . Fungicide resistance . Benzimidazole fungicides . Sterol demethylation inhibitors . β-tubulin gene
H. Shi : H. Wu : C. Zhang (*) : X. Shen Department of Crop Protection, Zhejiang Agriculture & Forestry University, Lin’an 311300, China e-mail: [email protected]
Introduction Strawberry leaf blight caused by Phomopsis obscurans is an important foliar disease in China and in many parts of the world. P. obscurans can infect foliage, runners, petioles, and fruits of strawberries (Eshenaur and Milholland 1989; Maas 1998). The foliar phase of this disease occurs most commonly in the field. Foliar lesions of P. obscurans are irregular and often circular, with a dark-brown centre surrounded by light-brown rings and purplish halos. Lesions become V-shaped as the disease develops, with the widest part toward the leaf margins. Serious infection results in defoliation, reduces yield, weakens plants, and affects winter survival (Nita et al. 2003a, b). Most commonly grown strawberry cultivars are susceptible to P. obscurans (Legard et al. 1997; Jia et al. 2005). Hence, significant losses in strawberry yields are likely to happen when growth conditions become favourable to this fungus. Applying fungicides such as benzimidazoles is the main strategy used in China. Benzimidazole fungicides including thiophanatemethyl and carbendazim have been widely applied on strawberries for more than 15 years in China. The decrease in efficacy and even the failure to control P. obscurans by carbendazim have been reported by growers in recent years. However, no published report of benzimidazole resistance was found for Phomopsis leaf blight. Sterol demethylation inhibitors (DMIs) such as tebuconazole have been applied on strawberries since 2003.
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