Evaluation of systemic acquired resistance (SAR) activators for the management of leaf blotch of apple caused by Marssonina coronaria

摘要

Marssonina leaf blotch caused by the fungus Marssonina coronaria (Ellis & J.J. Davis) Davis causing premature leaf fall, is relatively new threat to successful cultivation of apple in India. In India, this disease was first recorded in the year 1992 in Himachal Pradesh (8) and appeared in epiphytotic in the state in 1996 (7). It affects fruit size, colour, quality and fruit set adversely, reducing the tree vigour and fruit bearing capacity of the trees at the same time. Appearance of spots on the fruit makes it unsaleable in the market leading to direct economic losses to the growers. The disease can be kept at low levels by following protective fungicidal spray at short intervals during the growing season. This practice is in vogue in India also, particularly in Himachal Pradesh, where protective fungicidal spray programme is adopted every year to keep the disease under check (6). The use of resistant cultivars is an alternative to minimize the disease. In apple, however, it is difficult to develop resistant cultivars because of long juvenile phase and self incompatibility. Hence use of SAR activators in disease management seems a practical and environmentally safe option as compared to the current pesticide usage (10). Keeping in view the economic losses caused by the disease, present study was carried out to evaluate SAR activators against Marssonina leaf blotch in India.