Identificação e caracterização de plantas de feijão-caupi obtidas por meio de retrocruzamento resistentes aos vírus cowpea severe mosaic virus (CPSMV) e cowpea aphid borne mosaic virus (CABMV)

Abstract

Several diseases caused by different pathogen species can affect the cowpea culture, causing considerable reduction in its productive potential. Among the diseases of large occurrence are the viral illnesses. The viruses caused by the families Comoviridae and Potyviridae, represented by the species Cowpea severe mosaic virus (CPSMV) and Cowpea aphid-borne mosaic virus (CABMV) respectively, are considered of great importance. Considering the efficiency of the genetic resistance in the control of these diseases, this work was carried out aiming at the obtenttion and characterization cowpea plants with resistance to viruses CPSMV and CABMV, in order to obtain new and essentially derived cultivars. Eight crosses were performed using the line TE 97-309G-9 and the cultivar Patativa as parental donors of resistance to CPSMV and CABMV, and cultivars BR3-Tracuateua, BRS-Urubuquara, BRS-Novaera, BRS-Guariba and the landrace Pretinho as recurrent parents. The isolated virus used in the inoculation of F2 and F2RC1 plants were collected in Embrapa Meio-Norte experimental field, and maintained in differential lines. The purity of the isolated was evaluated and confirmed in the Laboratory of Fitovirologia, of Biological Institute, in São Paulo. Biparental crosses and triple were made to obtain F1 generations, and then submitted to self pollinated to develop F2 seeds. These F2 plants were inoculated with the mixture of the viruses CPSMV (sorotype I and II) and CABMV. Afterward, the resistant F2 plants were backcrossed with the respective recurrent parent to obtain F1RC1 seeds. The plants of F1RC1 generation were self pollinated to develop F2RC1 seeds. The F2RC1 plants were also inoculated with the same mixture of the viruses, as previously mentioned, and resistant plants were characterized. The following characters were used: number of days to the first flower; pod length; number of seeds per pod; weight of 100 seeds; seed color; and seed yield per plant. The segregation of the F2 generation of biparental crosses and triple and the F2RC1 were analyzed to check the expected frequency of 15 susceptible plants: 1 resistant plant by the χ2 (Qui square) test. All the F2 biparental crosses and F2RC1 backcrosses were adjusted to the expected frequency of 15:1. The characters evaluated in parents and F2RC1 were submitted to statistical analysis. The averages of the resistant plants F2RC1 in each backcross were compared with the average of respective recurrent parent by the t-test and the averages within crosses were compared by the Scott-Knott test. The existence of great genetic variability within and among backcrosses were detected based on all characters. It can be concluded by this study that all backcrosses are promising for obtaining essentially derived cultivars resistant to the viruses CPSMV and CABMV and that the backcrosses who obtained as recurrent parents cultivars BRS-Urubuquara and BRS Novaera are very promising for obtaining new cultivars with multiple resistance to the viruses CPSMV and CABMV.