Genetic analysis of the latent period of stripe rust in wheat seedlings

Genetics of slow-rusting resistance to yellow rust (Puccinia striiformis f.sp. tritici) was studied by a half-diallel design using six wheat varieties, Tiritea (susceptible), Tancred, Kotare, Otane, Karamu, and Briscard. The parents and 15 F-1 progenies were evaluated in the greenhouse by three pathotypes 7E18A(-), 38E0A(+), and 134E134A(+). The latent period was measured as the number of days from inoculation to the appearance of the first pustule. For each pathotype a randomized complete block design was used and data were analysed by methods of Griffing and Hayman. The range of average degree of dominance was from complete dominance to over-dominance. Positive and negative degrees of dominance were observed for each pathotype that showed the reversal of dominance. Analysis of variance showed the importance of both additive and dominance effects in controlling the latent period. Broad-sense heritabilities were 0.99 and narrow-sense heritabilities ranged from 0.85 to 0.94. Briscard and Karamu for the pathotypes 38E0A(+) and 134E134A(+), Kotare for the pathotype 7E18A(-) and Tancred for the pathotype 38E0A(+) had significant and positive general combining ability (GCA) (more resistance) for latent period. The crosses of Kotare with Tancred, Briscard and Karamu indicated the highest and positive specific combining ability (SCA) for the pathotype 7E18A(-). Significant additive genetic component and moderate narrow-sense heritability indicate the possibility of improving for longer latent period of stripe rust in breeding programmes.