Development of yellow corn germplasm with adequate level of resistance to bacterial stalk rot (Erwinia chrysanthemi) and diplodia ear rot (Diplodia macrospora)

Aside from Downy Mildew (DM), bacterial stalk-rot (BSR) is a considered major disease of corn especially when it occurs prior to physiological maturity, resulting in premature death of plants and yield loss due to poorly filled kernels. Diplodia ear rots (DER), on the other hand, are common during wet season and in hot humid corn growing areas, like the Philippines. Pesticides are not available and resistant maize cultivars are lacking. The lack of resistant cultivars to these two diseases is attributed to the unavailability of proven resistant germplasm. The yellow corn breeding program of IPB [Institute of Plant Breeding] have in the past selected several lines with adequate level of resistance to both diseases. However, there is a need to identify more sources of resistance to broaden the germplasm base for continued genetic progress. More than three hundred genotypes, consisting of inbred lines and populations were screened for resistance to these two major corn diseases for several seasons and locations. Of these, 18 inbreds and 13 populations were found to be consistently resistant to BSR, while 14 inbreds showed consistent resistance to DER. Four proven BSR resistant lines were Pi 52, Pi 53, Pi 54 and Pi 55. Genotypes found to exhibit resistance to more than one pathogen were S3YB 137-1-1-B (BSR, SER, DM), CA34503 (BSR, SER), TUPI 17-2-B (SER, DM), and 97-622 (BSR, DM). Genetic analysis showed that GCA was more important than SCA for both percent infection and lesion size in BSR. This indicates that additive gene effects are more important than non-additive gene effects in the expression of resistance to BSR. A BSR resistant synthetic population derived from resistant inbred lines and a BSR resistant population from IPB Var 1 were developed and tested as resistant.