H. A. MOHAMED, A. M. OMAR, A. K. A. SELIM and M. N. El-BARHAMTOUSHY
Faculty of Agriculture, Ain Shams University and Bahrim Experiment Station, Cairo, Egypt
I. Stripe rust
Inheritance of mature plant reaction to stripe rust of wheat was studied in six crosses making a dial between the four vulgare wheat cultivars Tosson, (Hindi 62 x Hindi 722), Kenya Farmer and F.K.N. These studies were carried out in season 1967-68 on F1, F2 populations and backcrosses where the epiphytotic of the natural infection during this season was severe.
According to mature plant reaction to stripe rust, the cultivars were classified in these classes -. ;
Resistant : F.K.N.
Moderately resistant : Kenya Farmer
Susceptible : Tosson and (Hindi 62 x Hindi 722)
Crosses studied were grouped in four groups:
(1) Moderately resistant x susceptible crosses:
This group was represented by two crosses, including Kenya Farmer as a moderately resistant parent crossed with each of the two susceptible cultivars Tosson and (H. 62 x H. 722). F1 of each cross was nearly as susceptible as the susceptible parents, showing nearly complete dominance of susceptibility to stripe rust. From these results, it could be suggested the presence of two duplicate genes (Ys1 and Ys2) for susceptibility carried by the susceptible cultivars Tosson and (H. 62 x H. 722) respectively, while their recessive alleles (ys1 and ys2 were carried by the moderately resistant Keyna Farmer cultivar.
(2) Resistant x Susceptible crosses:
This group was represented by two crosses including FKN as a resistant parent crossed with the susceptible cultivars Tosson and (H. 62 x H. 722). The F1 plants showed resistance to stripe rust (type 1), indicating incomplete dominance of resistance. Data indicated that resistance to stripe rust was due to the presence of three pairs of gene difference between the parents, and suggesting that the resistant parent carried one dominant gene for resistance. The resistant cultivar FKN might carry the dominant gene (Yr) for resistance, while for the two susceptible cultivars Tosson and (H. 62 x H. 722), it was suggested previously that they carried the two dominant duplicate genes for susceptibility (Ys1 and Ys2) respectively. Gene (Yr) for resistance was epistatic to genes Ys1 and Ys2 for susceptibility.
(3) Resistant x moderately resistant crosses:
This group was represented by the cross FKN x Kenya Farmer. All F1 plants showed resistance to stripe rust (Type 0) as in FKN parent, indicating complete dominance of resistance. Results indicated the presence of one pair of genes controlling resistance to stripe rust. The cultivar FKN was suggested to carry the dominant gene (Yr) for resistance, while the moderately resistant cultivar Kenya Farmer carried the recessive allele (yr).
(4) Susceptible x susceptible crosses:
One cross between the two susceptible parents Tosson and (H. 62 x H. 722), represented this group. The F1 plants, F2 population and progenies of backcrosses were all susceptible as the parents. It was previously suggested that the two duplicate genes for susceptibility (Ys1 and Ys2) respectively are found in the two parents. This conclusion agreed also with the results obtained in this group of crosses.
To explain the previous results, obtained from the F1, F2 and backcrosses of these four groups of crosses on a factorial basis, the following genes were suggested:
