Development of Inoculation Method for Testing Field Resistance to Sclerotinia Crown and Stem Rot in Alfalfa (Medicago sativa L.) and Evaluation of Cultivars.

Abstract

Alfalfa varieties and strains were evaluated for their resistance to Sclerotileia trlfoliorum ERIKS., the casual agent of Sclerotinia crown and stem rot (SCR) which is a serious disease in areas characterized by a warm and wet climate. Three experiments were carried out from 1983 to 1985, one under natural conditions for the infection and two under artificial inoculation in test fields. For the tests under artificial inoculation, all the varieties and strains were sowed in the field in September and were inoculated with cultured hyphae of SCR on the basal part of the plants in December. The disease severity was observed after 4 - 6 weeks. The symptoms of the disease were enhanced by the use of covering treatments after inoculation, and varietal differences in the severity of the disease were recognized based on the percentages of the plants which survived (Tables 3, 4, 5). A high correlation coefficient (r = - 0.798**) was obtained between the survival rate under artificial inoculation and the disease severity under natural infection (Fig. 1). It was suggested that this inoculation method which used hardening under natural conditions enabled to evaluate the resistance to SCR.