HERITABILITY ESTIMATES OF FIELD-RESISTANCE TO SPOT BLOTCH IN 4 SPRINGWHEAT CROSSES

Spot blotch of wheat (Triticum aestivum L.) caused by Bipolaris soroki niana (Sacc. in Sorok.) Shoem., is a major disease in South Asia. Popu lar commercial cultivars have low levels of resistance to spot blotch. Information on the inheritance of spot blotch resistance in wheat is lacking. Field studies were conducted in four wheat crosses. each invo lving a Chinese hexaploid parent with high levels of resistance and a commercial cultivar with low to intermediate levels of resistance to s pot blotch. Data were recorded in the F-2, F-3 and F-4 generations to estimate heritability. Field studies were conducted in three years (19 92-94) at Rampur, Nepal, involving 150 lines in each cross. The spot b lotch score was recorded as the percentage necrosis and associated chl orosis of the two upper most leaf surface. In the F-2 generation three spot blotch readings on the flag leaf were taken whereas in the F-3 a nd F-4 generations four readings were recorded at 5-day intervals on t he Bag and the penultimate leaves. The highest disease score (HDS) and the area under disease progress curve (AUDPC) were analysed. Heritabi lity (h(2)) estimates for spot blotch resistance were intermediate to high measured in terms of HDS (0.47 < h(2) < 0.67) and also AUDPC (0.5 8 < h(2) < 0.77) both in F-3 and F-4 generations in each of the four c rosses. Heritability values were somewhat higher for AUDPC than HDS. T here were significant negative correlations (r) of days to heading wit h HDS (-0.186 < r < -0.515) and AUDPC (-0.218 < r < -0.623). One-hundr ed kernel weight was significantly negatively correlated to AUDPC (-0. 245 < r < -0.454) in all crosses in each generation. The results sugge st that selection for resistance to spot blotch could be effective in the segregating populations generated from hexaploid wheat parents hav ing different levels of resistance. Although AUDPC appeared to be a be tter measure to determine genetic differences for spot blotch in wheat , HDS would be adequate in screening trials for resistance to spot blo tch.