SELECTION FOR SPOT BLOTCH RESISTANCE IN 4 SPRING WHEAT POPULATIONS

Spot blotch of wheat (Triticum aestivum L.), caused by Bipolaris sorok iniana (Sacc.)-Shoem, is a serious constraint in South Asia, and leadi ng cultivars have low levels of resistance. The response to selection for low and high area under disease progress curve (AUDPC) of spot blo tch in four wheat populations, involving different Chinese hexaploid p arents with high level of resistance and a commercial cultivar moderat ely resistant to spot blotch, was investigated. Selections were made i n the F-3 generation for low and high AUDPC of spot blotch and selecte d progenies evaluated in a replicated field test in the F-4 generation at Rampur, Nepal, in 1994. Selection in the F-3 for low and high AUDP C was effective in identifying F-4 lines with low and high AUDPC, resp ectively. Low AUDPC resulted in higher biomass and grain yield, higher harvest index, and 1000-kernel weight. On average, the low AUDPC line s headed later than the high AUDPC lines. Realized heritability estima tes for AUDPC were intermediate to high in magnitude (0.48 to 0.76). A UDPC was negatively correlated with biomass (r = -0.195 to -0.451), gr ain yield (r = -0.169 to -0.452), harvest index (r = -0.256 to -0.597) , days to heading (r = -0.319 to -0.570), and 1000-kernel weight (r = -0.322 to -0.530). Results indicate that selection for low AUDPC of sp ot blotch in segregating generations would be effective in identifying wheat lines with high levels of resistance and would have positive ef fects on other characters.