Selection Index for Improving Helminthosporium Leaf Blight Resistance, Maturity, and Kernel Weight in Spring Wheat

Abstract

Helminthosporium leaf blight [HLB, caused by spot blotch, Cochliobolus sativus (Ito & Kuribayashi) Drechs. ex Dastur, and/or tan spot, Pyrenophora tritici‐repentis (Died.) Drechs.], is the most serious disease constraint to wheat (Triticum aestivum L.) yields in the warmer plain areas of South Asia. A selection strategy is needed to identify early maturing, HLB‐resistant genotypes, given that most early maturing wheat cultivars in the region are either susceptible or have low levels of HLB resistance. A study was conducted to determine whether three traits could be simultaneously improved with a selection index (IS) combining the area under disease progress curve (AUDPC) as an assessment of disease severity, days to heading (DHD), and thousand‐kernel weight (TKW). Results from replicated field tests at two sites in Nepal in 2002 showed that selection in the F3 generation with the low and high IS was effective in identifying F4 lines with low and high AUDPC, respectively. The use of low IS was associated with higher grain yield and higher TKW, without significantly affecting DHD and plant height. The AUDPC was reduced by 579 to 837, depending on location and population, while TKW was increased by 7.8 to 12.7 g, and grain yield by 786 to 1491 kg ha−1 The use of IS also produced positive response in biomass and grain yields. There was an average 43% increase in grain yield of the low IS group compared with the high IS group. The results suggested that selection for early maturing, HLB‐resistant wheat lines with high grain yield and kernel weight is possible with a IS