Drought increases cowpea ( Vigna unguiculata [L.] Walp.) susceptibility to cowpea severe mosaic virus (CPSMV) at early stage of infection

Silva, Rodolpho G.G. and Vasconcelos, Ilka M. and Martins, Thiago F. and Varela, Anna L.N. and Souza, Pedro F.N. and Moreira Lobo, Ana Karla and Silva, Fredy D.A. and Silveira, Joaquim Albenisio Gomes and Oliveira, Jose T.A. (2016) Drought increases cowpea ( Vigna unguiculata [L.] Walp.) susceptibility to cowpea severe mosaic virus (CPSMV) at early stage of infection. Plant Physiology and Biochemistry, 109. pp. 91-102. ISSN 0981-9428

Abstract

The physiological and biochemical responses of a drought tolerant, virus-susceptible cowpea genotype exposed to drought stress (D), infected by Cowpea severe mosaic virus (CPSMV) (V), and to these two combined stresses (DV), at 2 and 6 days post viral inoculation (DPI), were evaluated. Gas exchange parameters (net photosynthesis, transpiration rate, stomatal conductance, and internal CO2 partial pressure) were reduced in D and DV at 2 and 6 DPI compared to control plants (C). Photosynthesis was reduced by stomatal and biochemical limitations. Water use efficiency increased at 2 DPI in D, DV, and V, but at 6 DPI only in D and DV compared to C. Photochemical parameters (effective quantum efficiency of photosystem II and electron transport rate) decreased in D and DV compared to C, especially at 6 DPI. The potential quantum efficiency of photosystem II did not change, indicating reversible photoinhibition of photosystem II. In DV, catalase decreased at 2 and 6 DPI, ascorbate peroxidase increased at 2 DPI, but decreased at 6 DPI. Hydrogen peroxide increased at 2 and 6 DPI. Peroxidase increased at 6 DPI and chitinase at 2 and 6 DPI. β-1,3-glucanase decreased in DV at 6 DPI compared to V. Drought increased cowpea susceptibility to CPSMV at 2 DPI, as verified by RT-PCR. However, at 6 DPI, the cowpea plants overcome this effect. Likewise, CPSMV increased the negative effects of drought at 2 DPI, but not at 6 DPI. It was concluded that the responses to combined stresses are not additive and cannot be extrapolated from the study of individual stresses.