Genetic control of resistance to soilborne wheat mosaic virus in Braziliancultivars of Triticum aestivum L. Thell.

In Southern Brazil, under ideal conditions Soilborne Wheat Mosaic Virus (SB WMV) induces yield reductions to the wheat crop of over 50%. The only effec tive way of controlling the disease is through resistance. However, the inh eritance of resistance is not been fully understood. The purpose of this wo rk was to study the genetic control of resistance to SBWMV. Crosses were ca rried out between the resistant wheat cultivar Embrapa 16 and the susceptib le cultivars BR 23 and IAC 5-Maringa, at the National Wheat Research Centre , Passo Fundo, RS, Brazil. The parents, F-1, F-2, and backcrosses were sown in plots in a field where soil was naturally infested with the vector of t he virus, the fungus Polymyxa graminis, in order to promote natural infecti on. All plants were individually evaluated for severity and type of lesions , according to a scale of 0 to 5, where, 0 = absence of symptoms and 5 = pl ants severely affected by mosaic plus dwarfing and rosetting. The statistic al analyses of the data showed broad sense heritability values between 43% and 55%. The data suggested the presence of two genes controlling resistanc e to SBWMV in the segregating population of both crosses.