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Assessing the vulnerability of wheat germplasm from Bangladesh and Nepal to Ug99 stem rust

Pretorius, Z. A., Prins, R., Malaker, P. K., Barma, N. C. D., Hakim, M. A., Thapa, D., Bansal, U., Cisar, G. L., Park, R. F.
Phytoparasitica 2015 v.43 no.5 pp. 637-645
Puccinia graminis, Triticum aestivum, alleles, cultivars, disease outbreaks, food security, germplasm, germplasm conservation, major genes, mature plants, pathogens, races, risk assessment, seedlings, stem rust, wheat, Bangladesh, Nepal
Bread wheat (Triticum aestivum) is an important crop in South Asia and epidemics of stem rust, caused by Puccinia graminis f. sp. tritici, can impact negatively on food security. In a pro-active assessment of the risk posed by this disease, germplasm collections received from Bangladesh and Nepal in 2011 were screened for their response to Sr31-virulent stem rust races belonging to the Ug99 group. According to a molecular marker assay, 44% of Bangladesh lines and 48% of Nepal lines contained Sr31. In seedling tests, most entries were susceptible to P. graminis f. sp. tritici race PTKST, confirming the ineffectiveness of Sr31. No lines contained Sr24 or Sr36, two major genes that have been overcome by races within the Ug99 group. Despite seedling susceptibility, many lines exhibited high levels of adult plant resistance in the field. The presence of the Sr2 marker allele of csSr2 in some of these lines indicated that this gene is likely to play a role in the adult plant resistance observed. This study showed that sufficient protection to Ug99 exists in Bangladesh and Nepal wheat germplasm, and that the appropriate release of resistant cultivars will insure against a possible future incursion of this dangerous pathogen.