Damage caused by cowpea mild mottle virus and Bemisia tabaci on conventional bean cultivars and on bean golden mosaic virus (BGMV) resistant transgenic isolines

Common bean is susceptible to several viral diseases including Bean golden mosaic virus (BGMV) and Cowpea mild mottle virus (CpMMV). Symptoms of CpMMV infection vary from mild mosaic to leaf crinkling depending on the cultivar, but there is no report of complete resistance. On the other hand, symptoms of BGMV infection results in quite severe golden mosaic, leaf malformation, and stunting, especially under early infection. Since both viruses are whitefly transmitted, double infection can be easily overlooked due to the much intense BGMV symptomatology. The development of Embrapa5.1 event of common bean resistant to BGMV (GM), and near isogenic lines to two commercial cultivars (Pérola and BRS Pontal) allows the evaluation of the damage caused by CpMMV by itself, since these transgenic isolines only get infected by CpMMV. The objective of this study was to determine the incidence and damage by CpMMV on the GM isolines and its correlation to the population level of Bemisia tabaci, in the absence of whitefly control. Field experiments were conducted in two experimental farms of Embrapa Rice and Beans in Santo Antonio de Goias (16°30’24,57” S; 49°17’06,53” W) and Brazabrantes (16°26’09, 20” S, 49°24’05,80” W), State of Goiás. Four isolines derived from cv. Pérola, and six from cv. BRS Pontal, the two parental commercial cultivars, and three other entries named IPR Eldorado, BRB 169, and CNFC 15882 were compared. The incidence of BGMV, CpMMV, number of whitefly eggs nymphs and adults were assessed as yield and yield components. The adult population of whiteflies was significantly lower in the GM lines derived from cv. Pérola (CNFCT 16201 and CNCF 16203) and from cv BRS Pontal (CNFCT 16205), as well as on the commercial cv. IPR Eldorado, access BRB 169 and line CNFP 15882. It was not observed significant differences in whitely eggs and nymphs among the GM isolines and other bean genotypes. Despite the low incidence of CpMMV in the GM isolines derived from cv. Pérola, yield of these isolines was lower than that for some of the isolines derived from cv BRS Pontal (CNFCT 16205, CNFCT 16206, CNFCT 16209, CNFCT 16210) which had a higher incidence of CpMMV. At the Brazabrantes field a higher disease incidence was observed. The yield for cv Pérola and BRS Pontal reached only 81 and 299 kg. ha-1, respectively, and were significantly lower than the GM lines derived from cv. Pérola (711 kg.ha-1) and cv. BRS Pontal (1073 kg.ha-1). The low yield of the conventional common bean parental cultivars as compared to the GM isolines was due to the severe occurrence of BGMV. The GM isolines derived from cv. Pérola and from cv. BRS Pontal yielded an average of 878% and 358% higher, respectively, than the conventional accesses. The GM isolines have yield potential even at conditions of high incidence of B. tabaci and the CpMMV if a management program for whiteflies including cultural practices and insecticides is established.