Breeding for resistance to spot blotch in wheat: Global perspective
1998
Ginkel, M. van | Rajaram, S.
Spot blotch (Bipolaris sorokiniana) is of increasing concern in developing countries. It mainly occurs in warm, humid wheat growing environments (ME5) in Latin America, Africa, the Indian Subcontinent, Southeast Asia, and China. More recently, spot blotch has also expanded into the cooler, traditional irrigated rice-wheat production areas (ME1), which may be due to pathogen adaptation, changes in varietal spectrum, reduction in tillage practices, a broader host-range, or climate modifications. In the hot and warm wheat production regions (ME5), wheat researchers consider spot blotch the number one economic pathogen. Total affected area is estimated at about 25 million ha. The lack of resistant, adapted cultivars is an urgent problem. Sources of spot blotch resistance are: Latin America (e.g., BH1146, CNT1), China (e.g., Shanghai 4, Suzhoe 8, and Yangmai 6), and wild relatives of wheat or alien species (e.g., Aegilops squarrosa, Thinopyrum curvifolium). One or six genes have been shown to be involved in resistance. No immunity in wheat is known. Low heritabilities, environmental components, and unknown variability in the pathogen may make breeding for resistance difficult. At CIMMYT, directed crosses are made between high yielding germplasm, adapted cultivars from target countries, and distinct sources of resistance. In Mexico, early generations are shuttled between Toluca (central highlands) and Cd. Obregon (coastal plains). Segregating germplasm is selected for resistance to diseases other than spot blotch, such as leaf and stem rusts, foliar blights, head scab, and for agronomic type, potential yield, and relative adaptive traits. ClMMYT's main testing site for spot blotch within Mexico is Poza Rica (21oN, 60 masl). Due to high temperatures and relative humidity, spot blotch is naturally prevalent.
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