Heritability estimates of field resistance to spot blotch in four spring wheat crosses

Abstract

Spot blotch of wheat {Triticum aestivum L.), caused by Bipolaris sorokiniana (Sacc. in Sorok.) Shoem., is a major disease m South Asia. Popular 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 involving a Chinese hexaploid parent with high levels of resistance and a commercial cultivar with low to intermediate levels of resistance to spot blotch. Data were recorded in the F,, F, and F4 generations to estimate heritabihty. Field studies were conducted in three years at Rampur. Nepal, involving 150 lines in each cross. The spot blotch score was recorded as the percentage necrosis and associated chlorosis of the two upper most leaf surface. In the ¥2 generation three spot blotch readings on the flag leaf were taken whereas in the F, and F4 generations four readings were recorded at 5-day intervals on the flag and the penultimate leaves. The highest disease score (HDS) and the area under disease progress curve (AUDPC) were analysed. Heritability {h^) estimates for spot blotch resistance were intermediate to high measured in terms of HDS (0.47 < /;-< 0.67) and also AUDPC (0.58 < h' < 0.77) both in F, and F4 generations in each of the four crosses. Heritability values were somewhat higher for AUDPC than HDS. There were significant negative correlations (r) of days to heading with HDS (-0.186 < r < -0.515) and AUDPC (-0.218 < r < -0.623). Onehundred kernel weight was significantly negatively correlated to AUDPC ( -0.245 < r < -0.454) in all crosses in each generation. The results suggest that selection for resistance to spot blotch could be effective in the segregating populations generated from hexaploid wheat parents having different levels of resistance. Although AUDPC appeared to be a better measure to determine genetic differences for spot blotch in wheat, HDS would be adequate in screening trials for resistance to spot blotch.

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

“…Pair-wise correlation coefficients between AUDPC and various agronomic traits were not consistent across the early-and late-heading groups of genotypes, except for DH and DM (Table 4).AUDPC was always negatively correlated with DH and DM. This shows that HLB severity is positively associated with earliness in wheat and supports the general observation among wheat scientists in South Asia that a genetic correlation exists between disease severity and earliness, making it difficult to combine early heading and HLB resistance (Duveiller & Gilchrist, 1994;Sharma et al, 1997b;Dubin et al, 1998;Duveiller et al, 1998). However, two recent studies have shown that HLB resistance and maturity are independently inherited (Sharma & Bhatta, 1999;Joshi et al, 2002), which suggests that selection for both these traits should be possible.…”

“…The lack of a significant correlation between AUDPC and plant height supports the previous finding by Joshi et al (2002) that resistance to spot blotch and plant height in wheat were independent. Sharma et al (1997b) and Dubin et al (1998) also reported a weak association between height and foliar blight severity. Our findings indicate that it could be possible to combine shorter plant height with HLB resistance which was also present in a few genotypes included in this study (Table 3).…”

Challenges to wheat production in South Asia

“…Shoem (syn. Helminthosporium sativum, teleomorph Cochliobolous sativus) is also considered an important disease in the eastern part of South Asia (Sharma et al 1997;Saari 1998;Pandey et al 2005;Siddique et al 2006;Joshi et al , 2007b. These countries are also getting support through regional nurseries and trials being organized by CIMMYT South Asia, Nepal out of which Eastern Gangetic Plains Screening Nursery (EGPSN) and Eastern Gangetic Plains Yield trial (EGPYT) have been proved very eVective in providing superior sources of resistance for spot blotch (Joshi et al 2007c).…”

Heritability estimates of spot blotch resistance and its association with other traits in spring wheat crosses

“…Srivastava et al (1971) reported that seedling resistance to spot blotch was controlled by two dominant epistatic genes. Similarly, Sharma and Bhatta (1999a) found that three dominant epistatic genes were involved in the genetic control of spot blotch. In a field study in Mexico, Velazquez (1994) reported that spot blotch resistance was partially dominant, with two to three genes conditioning adult plant resistance.…”