PATHOLOGICAL ACTIVITIES OF SCUTELLONEMA BRADYS MORPHOTYPES ON TWO ECONOMICALLY IMPORTANT YAM CULTIVARS IN CÔTE D’IVOIRE

Abstract

ABSTRACT. Scutellonema bradys is one of the most economically important pre-harvest and post-harvest nematodes of yams. Three morphotypes of S. bradys occur in Côte d’Ivoire, but their pathogenicity on yams is unknown. Therefore, this study assessed the pathogenicity of three S. bradys morphotypes (LNE-Sb, MCN-Sb, and SC-Sb) on two economically important yam cultivars in Côte d’Ivoire. The study comprised two trials conducted under greenhouse and post-harvest conditions. Each one-month-old yam plant, cultivated under greenhouse conditions, was inoculated with 1000 individuals of a morphotype of S. bradys. Under post-harvest conditions, each tuber was buried in 1 L of sterilized soil and infested with 500 individuals of a morphotype of S. bradys. Trials lasted four months after inoculation. The tuber’s sanitary state, dry rot index, final density, and reproductive fitness of the S. bradys morphotypes were assessed. Dry rot was observed on both freshly harvested and stored tubers. However, pathogenic activity varied among the morphotypes of S. bradys. The LNE-Sb morphotype from the dry tropical savannah zone caused the most severe dry rot (56.25% to 60.75% at harvest and 59.16% to 71.95% post-harvest). Its reproductive fitness on both yam cultivars ranged from 4.13 to 5.91. In contrast, the MCN-Sb morphotype from the transitional forest zone caused the least severe dry rot (15%), and reproductive fitness varied between 1.70 and 2.97 on both yam cultivars. The morphotypes of S. bradys exhibited varying levels of pathogenicity on yams. The morphotype from the dry tropical savannah zone was the most aggressive and reproductive, unlike that of the transitional forest zone. Effective management of S. bradys populations is essential to protect and sustain this source of income for yam farmers and traders in Côte d’Ivoire.