Abstract
The objective of this work was to identify new sources of simple and multiple resistances to Cowpea severe mosaic virus (CPSMV), Cowpea aphid-borne mosaic virus (CABMV) and Cucumber mosaic virus (CMV) isolates in cowpea (Vigna unguiculata). Thirty-three genotypes from the germplasm bank of Universidade Federal do Ceará were tested as to their resistance to four CPSMV isolates, two CABMV isolates and one CMV isolate. Twenty-five days after the first virus inoculations, all inoculated plants, including the asymptomatic ones, were tested by serology. Genotypes were classified as: immune, plants without symptoms and negative serology; resistant, plants with mild mosaic and positive serology; susceptible, plants with mosaic and positive serology; and highly susceptible, plants with severe mosaic, other systemic symptoms, including systemic necrosis, and positive serology. Simple and multiple resistances to viruses were identified among the evaluated genotypes, but none of them showed multiple immunities to all isolates. Four genotypes showed immunity to all CPSMV isolates, two were immune to CABMV and two showed immunity to CMV. Eleven genotypes showed multiple resistances to two viruses, allowing for the development of new cultivars with more stable and broader resistance. Genotypes Purple Knuckle Hull-55, MNC-03-731C-21 and CNCx284-66E show resistance to CABMV, even when inoculated with CMV.
Highlights
Cowpea [Vigna unguiculata (L.) Walp., subspecies unguiculata] is a major source of protein with considerable importance for human nutrition in the semiarid and tropical regions of Northeastern Brazil
The following Cowpea severe mosaic virus (CPSMV) isolates were used in the evaluation of the cowpea genotypes: CPSMVCE, the first characterized isolate obtained from cowpea in Ceará (Lima & Nelson, 1973); CPSMVMC, an isolate with the capacity to infect 'Macaibo', a cowpea cultivar immune to most isolates of CPSMV (Lima et al, 1998); CPSMVCROT, isolated from Crotalaria paulinea L. in the state of Maranhão (Lima et al, 2005a); and CPSMVPB, an isolate recently obtained from cowpea in the state of Paraíba
The isolate CPSMVMC infected the Macaibo cultivar, which is immune to all other CPSMV isolates, it caused less severe symptoms on the other cowpea genotypes than the other CPSMV isolates (Table 1), confirming previous studies (Camarço et al, 2009)
Summary
Cowpea [Vigna unguiculata (L.) Walp., subspecies unguiculata] is a major source of protein with considerable importance for human nutrition in the semiarid and tropical regions of Northeastern Brazil. The North and Northeast of Brazil are the largest producer areas, and the state of Ceará is considered the greatest producer in the country (Freire Filho et al, 2005; Lima et al, 2005b). This leguminous crop is of strategic importance for small farmers and an option for the agribusiness of the North and Northeast of Brazil. Viral diseases have been considered one of the most important sanitary problems in cowpea in the state of Ceará, causing serious reductions in crop productivity (Lima & Nelson, 1973; Lima et al, 2005b)
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