Yield loss in Guinea yam (<i>Dioscorea rotundata poir.</i>) due to infection by <i>Yam mosaic virus</i> (YMV) genus <i>Potyvirus</i>

Abstract

An experiment was conducted to investigate the influence of Yam mosaic virus (YMV) genus Potyvirus on the tuber yield of Dioscorea rotundata based on assessment of comparative performance of inoculated and uninoculated plants of two genotypes (TDr 93-31 and TDr 95-127). Symptoms of virus infection were evident on inoculated plants especially at four weeks after inoculation. Visual virus symptom severity scores had significant (P<0.0001) correlations with enzyme-linked immunosorbent assay (ELISA) readings (r = 0.7), leaf chlorophyll content (r = -0.9), and tuber yields (r = -0.9). Stomatal conductance results showed higher values (P < 0.001) of diffusive resistance in virus-infected leaves compared to virus-free leaves. The leaf area per plant, leaf dry weight, vine dry weight, and tuber dry weight were less (P< 0.001) in inoculated plants compared to uninoculated plants for both genotypes at 10, 18 and 24 weeks after inoculation. Similarly lower values for leaf area index (P > 0.004), harvest index (P < 0.01), leaf chlorophyll content, and intercepted  photosynthetically active radiation (P = 0.01) were obtained from plots with inoculated plants. YMV infection in D. rotundata resulted in a yield loss of 65.4% in TDr 93-31 and 52.6% in TDr 95-127. Reduced capacity for photosynthesis in YMV infected plants, due to increased diffusive resistance of stomata, as well as reduced leaf area and chlorophyll content, contributed significantly (P < 0.001) to their reduced tuber yields. The economic importance of the virus is thus established as it can result in significant loss to resource-poor farmers.

Keywords: Dioscorea rotundata, TAS-ELISA, yield loss, Yam mosaic virus (YMV) genus Potyvirus.