Selection for Spot Blotch Resistance in Four Spring Wheat Populations

Abstract

Spot blotch of wheat (Triticum aestivum L.), caused by Bipolaris sorokiniana (Sacc.) Shoem, is serious constraint in South Asia, and leading cultivars have low levels of resistance. The response to selection for low and high area under disease progress curve (AUDPC) of spot blotch in four wheat populations, involving different Chinese hexaploid parents with high level of resistance and a commercial cultivar moderately resistant to spot blotch, was investigated. Selections were made in the F3 generation for low and high AUDPC of spot blotch and selected progenies evaluated in a replicated field test in the F4 generation at Rampur, Nepal, in 1994. Selection in the F3 for low and high AUDPC was effective in identifying F4 lines with low and high AUDPC, respectively. Low AUDPC resulted in higher biomass and grain yield, higher harvest index, and 1000‐kernel weight. On average, the low AUDPC lines headed later than the high AUDPC lines. Realized heritability estimates for AUDPC were intermediate to high in magnitude (0.48 to 0.76). AUDPC was negatively correlated with biomass (r = −0.195 to −0.451), grain 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 spot blotch in segregating generations would be effective in identifying wheat lines with high levels of resistance and would have positive effects on other characters.

Resistance to Helminthosporium leaf blight and agronomic performance of spring wheat genotypes of diverse origins

“…There was a significant negative correlation between AUDPC and heading or maturity confirming the difficulty experienced by wheat scientists in South Asia attempting to improve these two important traits simultaneously (Sharma et al, 1997a;Dubin et al, 1998). However, the magnitude of correlation between AUDPC and heading especially for long duration genotypes (r = 0.421) underlines the possibility of identifying early maturing resistant genotypes in segregating generations as suggested by Sharma & Figure 1.…”

“…Disease assessment was started when necrotic symptoms appeared on the penultimate leaves. Disease severity was recorded by visually scoring the percent diseased area of the flag (F) and penultimate (F-1) leaves (da Luz & Bergstrom, 1986;Sharma et al, 1997a). Four disease readings were recorded between 85 and 106 days after sowing, at intervals of 5 to 7 days.…”

The effect of spot blotch and heat stress on variation of canopy temperature depression, chlorophyll fluorescence and chlorophyll content of hexaploid wheat genotypes

“…Disease assessment Ten primary tillers within each plot were randomly tagged to score spot blotch severities, which were recorded by visually scoring the percentage diseased area of the flag (F) and penultimate (F-1) leaves (Sharma et al 1997). Three disease readings were recorded between growth stages DC 69 and 83 (Zadoks et al 1974), at 5-7-day intervals.…”

Farmer participatory evaluation confirms higher grain yields in spring wheat using a selection index for spot blotch resistance, maturity and kernel weight

“…However, Sharma and Bhatta (1999) and Joshi et al (2002) reported that the days to heading and spot blotch resistance segregated independently in crosses involving early-maturing susceptible and late-maturing resistant genotypes. Sharma et al (1997a) showed that kernel weight and spot blotch resistance were not correlated in some of the crosses involving a well-adapted susceptible cultivar with high grain weight and a less well-adapted resistant genotype with low grain weight. Adapted susceptible wheat cultivars in South Asia show high kernel weight primarily because of early maturity, while the less well-adapted resistant genotypes have a low kernel weight because of their late maturity, a negative characteristic in warm wheat-growing environments because the longer grain filling period is curtailed by high temperatures (Dubin et al, 1998;Sharma et al, 2004a).…”

“…Considering independent segregation of maturity and spot blotch resistance (Sharma & Bhatta, 1999;Joshi et al, 2002) and the absence of a negative correlation between grain weight and resistance (Sharma et al, 1997a), Sharma and Duveiller (2003) successfully used a selection index to simultaneously improve resistance, maturity and grain weight in the F 4 generation. These three traits determine the commercial acceptance of a wheat cultivar in the region.…”