Inheritance of resistance to the bipartite Tomato chlorotic mottle begomovirus derived from Lycopersicon esculentum cv. 'Tyking'

Severe outbreaks of bipartite begomoviruses ( family Geminiviridae) have been observed on tomatoes after the introduction of the whitefly Bemisia tabaci ( biotype B) in Brazil. The Lycopersicon esculentum line 'TX 468-RG' was identified as one of the best sources of broad-spectrum resistance to species comprising the tomato-infecting Begomovirus complex in Brazil. The genetic basis of resistance to one Begomovirus isolate was investigated using populations from the cross between 'TX 468-RG' (P-1) and the susceptible line 'Ohio 8245' (P-2). Parental lines, F-1, backcross (BC) to P-1 and BC to P-2 and F-2 generations were inoculated at the two true-leaf stage using 20 viruliferous whiteflies per plant. Assessment was done two weeks after inoculation based upon visual analysis of symptom expression. The ratio of resistant to susceptible plants closely fit to a single recessive gene ( locus) model. The sequence analysis indicated that the Begomovirus isolate used in this assay was closely related to the bipartite Tomato chlorotic mottle virus. Therefore, this gene/locus, was tentatively named tcm-1 ( tomato chlorotic mottle virus resistance-1). This locus has been transferred to distinct tomato cultivars and levels of resistance similar to that of 'TX 468-RG' were observed in advanced (F-8 and F-9) generations. In addition, breeding lines carrying the tcm-1 locus were also resistant to other Brazilian bipartite tomato-infecting Begomovirus species.