Corn pathology research of Pioneer in the Philippines
1987
Dalmacio, S.C. | Lozano, G. | Cordero, F. | Yadao, A.
Inoculation experiments proved that Diplodia macrospora was the cause of leaf blight, ear rot and stalk rot of corn. Symptoms of the three phases of infection are described. Studies on metalaxyl fungicide showed that the chemical was capable of eradicating established downy mildew infection on corn. The implications of this result in DM [downy mildew] resistance breeding and other research areas are given. Studies also showed that metalaxyl fungicide gave complete control of downy mildew at rates as low as 0.2 g ai/kg seed. On the other hand, the recommended rate of 2 g ai/kg showed some detrimental effect on seed germination. Using a stalk inoculator for bacterial rot screening, good sources of resistance to the disease among existing Pioneer corn inbreds have been identified. On the other hand, presently grown commercial corn hybrids showed inadequate resistance to bacterial rot with infection ranging from 53 to 85%. There was good correlation (r = 0.83) between percent infection and yield loss. Results of a study on the comparative virulence of three isolates of Erwinia carotova pv chrysanthemi showed isolate IPB 24 as the most virulent and isolate R8, an isolate from rice, as the least virulent. Among the eight methods tried for inoculating corn with Rhizoctonia solani, the whorl inoculation using sclerotial bodies showed the highest percent infection (98%), followed by leafsheath inoculation using infested sorghum grains (92%) and whorl inoculation using infested sorghum grains (67%). Of these three, leafsheath inoculation method was adopted as the standard method in screening for resistance to banded leaf disease because it stimulates natural infection pattern by the fungus. Results of the most recent trial showing great variation in all parameters measured are determined.
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