Influence of Field and Storage Diseases and Pests on Tuber Yield and Quality of Exotic and Local Yam (Dioscorea spp.) Genotypes

Abstract

Field and storage trials were conducted to assess the response of exotic and local yam genotypes to major diseases (anthracnose, yam mosaic virus (YMV) and dry rot) and pests (i.e., mealy bug and nematodes) for the identification of parents with desired complementary traits for crossing. The experiment was conducted at the Njala Agricultural Research Centre (NARC) experimental site in Sierra Leone during two cropping seasons, 2020 and 2021. A total of 113 genotypes of yam comprising 15 D. rotundata, 4 D. prahensilis, 7 D. esculenta, 74 D. alata, 7 D. bulbifera, and 4 D. cayenensis were assessed. Results showed a significant (p < 0.001) linear relationship between yield and disease severity among yam genotypes. In-field disease (anthracnose and yam mosaic virus) infection accounted for 38% of the total variation observed in the fresh tuber yield. Findings on fresh tuber yield revealed that for every ton increase in yield of yams, anthracnose and YMV severities at five months after planting (MAP) decreased by 0.5 and 3.1 units, respectively. About 30 genotypes had low infection of disease, of which two belonged to D. rotundata (TDr 205 and TDr 96/00587), two belonged to D. prahensilis (PSLY074-13 and BMSLY085-13), three belonged to D. bulbifera (MOSLY022-12, MOSLY024-12 and KESLY09-12), and one belonged to D. esculenta (WRSLY083-13), while the remaining were D. alata. About 27 genotypes had intermediate infection, and 14 had high disease susceptibility, all of which belonged to D. alata. Storage disease infection had a highly significant (p < 0.002) linear relationship among yam genotypes. Dry rot, mealy bug, and nematode infection accounted for 15.1% of the total variation in fresh tuber weight loss. The findings were relevant for selecting parents with complementary traits of interest targeted at yam population improvement.