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Abstract: Seven hundred twenty-nine lines of diverse wheat germplasm lines were evaluated in eight locations of three countries (India, Nepal and Bangladesh) of South Asia for 5 years (1999–2000 to 2003–2004) through Eastern Gangetic Plains Screening Nursery (EGPSN) organized by CIMMYT South Asia, Nepal, for agronomic performance and tolerance to spot blotch of wheat. Each year, the number of lines represented a new set of 150 lines that included six common checks and a different local check at each of the eight locations. One hundred and five lines, 21 in each year, advanced from EGPSN were also tested for 5 years (2000–2001 to 2004–2005) in five locations of South Asia through Eastern Gangetic Plains Yield Trials (EGPYT) to verify spot blotch tolerance and superior yield performance of the selected germplasm. Many lines yielded significantly more than the best check and possessed high levels of spot blotch resistance under warm humid environments of South Asia. The most promising 25 lines have been listed as sources of strong resistance, with 9 lines better yielding than the best resistant check PBW 343 in fewer days to maturity. Most of these superior lines represented elite CIMMYT germplasm and around half were derived from Kauz and Veery. The line EGPYT 67, Kauz//Kauz/Star/3/Prinia/4/Milan/Kauz, was the best for spot blotch resistance, yield, days to maturity, and 1000 grain weight (TKW). The next two lines in the order of merit were EGPYT 84 (Mrng/Buc//Blo/Pvn/3/Pjb 81) and EGPYT 69 (Chirya3/Pastor). The results demonstrate that additional spot blotch resistant wheat genotypes with high grain yield and TKW, and early maturity, have become available as a result of the regional and international collaboration in South Asia. [Copyright &y& Elsevier]

Foliar blight is a major biotic constraint to wheat in the Gangetic plains of south Asia, particularly in the rice-wheat system. The disease occurs as a complex of spot blotch and tan spot caused by C. sativus and P. tritici-repentis, respectively. Yield losses reach on average 15% but are variable depending on sowing time, years, locations and stress conditions. Resistance breeding has been the cornerstone of the control strategy. Through international agricultural research efforts in collaboration with National Agricultural Research Systems (NARS), resistance sources from China, Zambia and Brazil were identified and novel germplasm such as synthetic hexaploid wheats derived from crosses with Aegilops tauschiiand tetraploid wheat were generated. Materials resulting from these pre-breeding activities are now combined to adapted spring wheat to produce new high yielding genotypes showing a lower disease progress. Ongoing regional efforts include several wheat nurseries jointly organized by CIMMYT and NARS and specially targeted for warmer wheat growing areas. The stability of resistant genetic stocks remains essential considering that C. sativusis non-specific and forms a continuum of strains that may change rapidly. Although high moisture and temperature are known to favor the disease, little information is available on the exact role of climatic factors on symptom development. Stress factors appear to influence to a great extent disease progress and epidemics, suggesting that crop management practices are a critical component of an integrated disease control. Thus, understanding their role on foliar blight seems imperative when the increasing adoption of zero tillage in rice-wheat may affect inoculum survival and when genotypes more adapted to new tillage practices will be required. The role of alternate hosts and the source of primary inoculum in rice-wheat systems are still not well documented but indications suggest that seed may play an important role in... [ABSTRACT FROM AUTHOR]

A number of exotic wheat (Triticum aestivum) genotypes resistant to spot blotch caused by Cochliobolus sativus are being used to improve the resistance of commercial cultivars in the warm regions of South Asia. The objective of the present study was to determine the inheritance of field resistance to spot blotch in two resistant (R) wheat genotypes, 'Chirya.3' and 'Milan/Shanghai #7' (MS#7), which were crossed to a susceptible (S) commercial cultivar, 'BL1473.' The two resistant genotypes also were crossed to determine allelic relationships for resistance between them. Spot blotch severity was recorded on the parents and on F1, F2, and F3 progenies. The F1 plants from the two crosses between susceptible and resistant genotypes had low disease severity like the resistant parents, indicating that resistance in Chirya.3 and MS#7 is conditioned by dominant gene action. The F2 plants segregated in 3R:1S ratios, and the F2.3 families showed the ratio of 1R:1S:2S, segregating for R and S, suggesting that resistance in the two resistant parents is conditioned by a single, dominant gene. The F1 plants from the cross between the two resistant genotypes were resistant, whereas their F2 progenies segregated in 15R:1S, suggesting that the resistance genes in MS#7 and Chirya.3 are nonallelic. These simply inherited sources of resistance could be useful for improving spot blotch resistance in the warm regions of South Asia and also may offer useful diversity to breeding programs for developing spot-blotch-resistant wheat cultivars in other regions. [ABSTRACT FROM AUTHOR]