GENETICS OF LEAF RUST RESISTANCE IN FOUR SYNTHETIC HEXAPLOID WHEATS

Abstract

The genetic variability of Triticum tauschii has been used in Triticum aestivum L. breeding through the generation of synthetic hexaploid wheats (SH) (Triticum turgidum x Triticum tauschii). In Triticum tauschii the genetic resistance to diseases is the trait most utilized, including resistance to leaf rust (Puccinia recondita f. sp. tritici) of wheat. The genetics of resistance to leaf rust in four SH, developed by the Wheat Wide Cross Program of the International Maize and Wheat Improvement Center (CIMMYT) was studied. The SH 1 was crossed with hexaploid wheats Morocco, Opata 85 and Sonora 64, whereas, SH 2, SH 3 and SH 4 were crossed only with Morocco. The F₂, F₃, and BC_lF₂ generations from the crosses SH 1 x Morocco and SH 2 x Morocco, and the F3 generations from SH 1 x Opata 85 and Sonora 64 crosses were tested with diferent leaf rust races. F₂ and F₃ generations of SH 3 x Morocco and SH 4 x Morocco were also tested. The data showed that the degree of seedling resistance, was somewhat less in the synthetic hexaploids than in the diploid or tetraploid parents. Each of the SH 1 and SH 2 carried a single recessive gene for resistance. Resistance was suppresed in SH3, and SH 4. In the field evaluation of the resistant F₃ lines of the crosses Morocco x SH 1 and SH 2 were susceptible to the MCJ/SP race.