Collection and pathogenicity of yam Anthracnose (Colletotrichum gloresporioides) isolates and host variants x isolate interaction

This study was conducted to evaluate the reaction of different yam varieties to different isolates of Colletotrichum gloresporioides and also to determine the most virulent isolate of the pathogen. Ten varieties/accessions of yam were used and planted in pots and in the field. The varieties served as treatments which were replicated ten times. In the field, the experiment was laid out in RCBD manner, each plot consisted of ten plants replicated three times. Five isolates of the pathogen were collected, isolated, cultured and incubated in the laboratory. Data on disease severity rating using the rating scale of Repoche et. al. (2008) and yield data were collected. The ten different varieties of yam showed varied reactions to the pathogen when evaluated under screenhouse (pot experiment) and field conditions. In the pot experiment, LA359 showed resistance having lowest disease severity rating and high percentage of marketable tubers at harvest VU1, VU2, VU3, VU4 and VU5 were found susceptible to the disease with VU8 as the most susceptible. Field evaluation of the different varieties showed that VU5 was the most resistant showing a low disease severity rating of 1.6 (15%) and corresponding high weight of yield and percent marketable tubers. Based on the disease rating, VU3, VU4, VU6 exhibited necrosis ranging from 6-20%; VU7, VU2, VU1, with 21 to 50%; VU8, LA359 and Inopacan White with 51 to 75%. While some of the varieties may be resistant under field condition, this should be further evaluated to confirm their resistance. Of the five isolates tested, the Mahaplag, Leyte isolate was found to be the most virulent causing high degree of infection to most of the varieties compared with the other isolates. VU5, which was found to be resistant under natural field infection, was found susceptible when inoculated with the Mahaplag isolate. Regardless of the isolate, VU2 and Inopacan White were the most susceptible. In devising an IPM approach to the anthracnose disease it is important that the identity of the existing pathogen isolate be known. The use of resistant variety should also be an integral part of the production system with the objective of reducing the anthracnose disease in yam.