Variation and Genotype x Environment Interaction Studies for Resistance to Leaf and Stripe Rust Disease in Spring Wheat (Triticum aestivum L.)

Wheat is a cereal crop of global importance. Consumed as a staple food in many countries, the international trade of wheat and its price has implications for global political stability in which its import is a subsistance food. As such, a stable global supply of wheat is a global necessity. In the United States and many other countries it is threatened by two fungal diseases viz., leaf and stripe rust which cause significant yield losses on an annual basis. With this in mind, the variability in resistance to leaf and stripe rust in three unique breeding trials (each consisting 40 genotypes) was evaluated at six different locations across Texas. Analysis of variance revealed significant differences among the genotypes for area under the disease progression curve (AUDPC) and disease susceptibility (DS) in response to leaf and stripe rust in all three trials. The G x E interaction across locations also exhibited highly significant difference for AUDPC and DS among the genotypes in all sets. Based on reaction type (mean of six locations) at dough growth stages, genotypes were grouped into resistant, moderately resistant, moderately susceptible and susceptible. In the TAMU-TIA 50%, TAMU-TIAP1 35% and TAMU-TIAP2 37.5% of the genotypes were resistant for leaf rust while 27%, 17.5 % and 17.5% were resistant for stripe rust followed by moderately resistant, moderately susceptible and susceptible genotypes. In terms of a higher AUDPC, the Uvalde, Texas location was the most severe for TIA and TIAP1 population and Castroville for the TIAP2 population for leaf rust, while Mcgreger, Texas showed a higher AUDPC for stripe rust in all three trials. Along with disease severity leaf-tip necrosis (Ltn) expression which has been associated with the expression of adult plant resistance to leaf and stripe rust was also visually recorded and compared with the degree of DS and found that genotypes having a complete expression of Ltn exhibited low (either trace or resistance) DS for leaf rust. This indicates that they might possess the Lr34/Lr36 genes responsible for their adult plant resistance, for confirmation of this molecular work is in progress. 

Key Words: Wheat, Triticum aestivum, Ltn, Leaf rust, Stripe rust, Resistance, AUDPC

Presenting author's email: rprasadbhugpb@gmail.com