VECTOR POPULATION, INCIDENCE AND SEVERITY OF THREE VIRUSES OF SOME SOYBEAN (GLYCINE MAX [L.] MERILL) VARIETIES IN IBADAN, DERIVED SAVANNAH AGRO-ECOLOGY

Abstract

Soybean crop is the richest source of complete plant protein, essential for human nutrition. The crop is susceptible to several viruses prevailing in Nigeria. This study was undertaken to investigate the occurrence of natural infections of viruses and their vectors on five soybean varieties, and evaluate the yield and resistance status of the varieties. The experiment was conducted at the National Cereal Research Institute Experimental Field, Ibadan station in 2017 and 2018 planting season and laid-out in a Randomized Complete Block Design with three replications. Each plot size was 4 m x 1.5 m. Leaf samples showing virus-like symptoms were collected and tested for Soybean mosaic virus (SMV), Cowpea mottle virus (CMeV) and Cowpea mild mottle virus (CPMMV) using direct antigen coating-enzyme-linked immunosorbent assay (DAC-ELISA). Insect vector counts was carried out weekly using insect traps. It was observed in both years that the percentage insect counts was high at 4 week after planting (WAP) then peak at 6 WAP and later declined from 6 to 8 WAP for both Bemisia tabaci and Aphis glycines. The variety differed significantly in virus disease incidence and severity. All the varieties tested positive for CPMMV and negative for SMV in both years. TGX 1904 and TGX 1835-10F in 2018 tested positive for CMeV. TGX 1448- 2E produced significantly (P ≤ 0.05) higher grain yield of 3785.7 kg/ha than other varieties in 2017, it also had significantly (P ≤ 0.05) higher grain yield of 3235.4 kg/ha than TGX 1904- 6F (1007 kg/ha), TGX 1835-10F (1429.6 kg/ha) and TGX 1987-10F (1737.7 kg/ha) in 2018. Only TGX 1987-62F is resistant to the viruses. CPMMV transmitted by B. tabaci is the most prevalent virus associated with soybean in the study area. Some symptomatic soybean varieties tested negative to the three viruses, hence, further studies involving diagnostic test for more viruses is recommended to ascertain their resistance status.