Morphological and molecular characterization of powdery mildew on sunflower (Helianthus annuus L.), alternate hosts and weeds commonly found in and around sunflower fields in India

摘要

Powdery mildew has become a regular and serious problem on sunflower in India during the past decade. Powdery mildew infected leaves were collected from ten regions in seven major sunflower growing states of India representing kharif, rabi and spring cultivation. Anamorph characteristics were studied to identify the pathogen. Five isolates from each of the location were subjected to molecular analysis using universal primers specific to Erysiphales and the ITS primers specific to three species of powdery mildew (Golovinomyces orontii, Podosphaera xanthii, Leveillula taurica) reported to infect sunflower. Further, the pathogen infecting weeds in sunflower fields, cucumber crops grown in the vicinity of sunflower fields and perpetuating on two wild Helianthus species (H. strumosus, H. hirsutus) for 7 years was characterized. Morphological, molecular and sequence analysis confirmed the fungi infecting sunflower including the wild species as G. orontii. Members of Cucurbitaceae were infected by P. xanthii with the exception of Coccinia sps and Luffa acutangula which showed infection of G. orontii. Common beans, Zinnia elegans and Euphorbia hirta revealed infection of G. orontii while other crops showed infection of P. xanthii. None of the powdery mildew samples showed infection of Leveillula taurica. Blast analysis of the ITS sequences and characteristics of the anamorphs were mostly in agreement with the respective pathogen except for E. hirta which were dimorphic, large and paramoecium shaped. Cross infectivity studies of the pathogen isolated from cucurbits and sprayed on sunflower failed to infect while those from wild sunflowers and Z. elegans caused infection.