Effect of Heterogeneous Populations on Yield and Spread of Stem Rust in Triticum Durum

A multiline development programme was started to introduce diversity of genes for stem rust resistance in two durum varieties, namely NI 146 and HD 4519, through backcrosses using 14 diverse donors. Susceptible components 1a pure, stand showed high rate of rust spread leading to high rust incidence. Multilines showed significantly low rate (67.4% to 84.0%) of rust spread over the mean spreads of their individual components and maintained high degree of population resistance. The susceptibility level of multilines did not increase proportionately with increase In the percentage of susceptible components in the multiline population. The multiline populations showed up to 8.5% increase in yield over the mean yields of their components, considered individually, and gave significantly higher yields (15.5% to 21.0%) over the most susceptible component under heavy disease pressure. Even if 40% of the components of a multiline were susceptible to the most dominant and prevalent races of stem rust, their composite population behaved like a resistant line having no adverse effect on yield. Compared to the recurrent variety, multilines also showed better yield potential over locations.