Authors: ETIENNE DUVEILLER, R. C. SHARMA, D. MERCADO, H. MARAITE, M. R. BHATTA, G. ORTIZ-FERRARA, D. SHARMA
Abstract: 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 tauschii and 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. On-going 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. sativus is 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 disease transmission. Seed treatment may prove useful as a part of an integrated disease management approach based on improved resistance and good agronomy.
Keywords: Breeding zero tillage, Foliar blight, Resistance breeding, Wheat
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