Effect of Temperature on Symptoms Expression and Viral RNA Accumulation in Groundnut Bud Necrosis Virus Infected Vigna unguiculata.

Groundnut bud necrosis virus (GBNV) (Tospovirus genus, Bunyaviridae family) infects the major crops of solanaceae, leguminosae and cucurbitaceae in India. Temperature is an important factor which influences the plant growth and development under diseased conditions.

In the present study, we evaluated the effect of four different temperatures on the symptoms expression and viral RNA accumulation in the GBNV inoculated cowpea plants.For the evaluation of viral symptoms and RNA accumulation, we used 2-3 leaf stage cowpea plants grown in the controlled conditions. GBNV was mechanically inoculated by sap method to the cowpea plants and inoculated plants were incubated at four different temperatures (30, 25, 20 and 15 °C).

The first visible symptom of GBNV infection at the inoculated site was observed in the form of chlorotic spots which were converted into the necrotic spots as the infections succeeded. Some yellow mosaic symptoms were also observed at the systemic site during viral infection cycle. Plants incubated at higher (30 and 25 °C) temperatures showed a severe necrosis and a higher viral RNA accumulation at the inoculated site and facilitated the viral spread at the systemic site. However, viral RNA accumulation was less at the systemic site than the inoculated site. In contrast, symptoms' expression and viral RNA accumulation were decreased at the inoculated site at low (20 and 15 °C) temperatures, no viral symptoms were observed at the systemic site (15 °C); in addition to viral RNA accumulation suppression at this site. GBNV infection at the inoculated site induced the higher accumulation of H₂O₂ followed by the induction of cell death at higher temperatures (30 and 25 °C) than the lower (20 and 15 °C) temperatures.

This study suggests that viral RNA accumulation parallels with the H₂O₂ production and induction of cell death by GBNV infection in cowpea plants is temperature dependent.