Corn leaf aphid and polysora rust resistance in tropical maize

xiii, 86 leavesThis research includes two separate studies both of which incorporated generation mean analyses to interpret genetically the resistance to com leaf aphid and polysora rust in tropical maize. The first study focused on resistance to corn leaf aphid in tropical sweet corn inbred Hi38-71. An inoculation technique using hair-pin clip cages and infestation quantification method using digital image analysis were developed for this study. During the study, a heavy natural infestation of com leaf aphids occurred in a seed production nursery. Yield loss by ranged from 38.9% to 98.8%, with an average loss of 71.7%. The clip-cage method was effective in distinguishing resistant and susceptible plants under field conditions. Resistance to com leaf aphid from Hi38-71 appeared to be monogenic and recessive. Aphid reproduction and population growth were measured on four different genotypes of varying aphid tolerance. Aphids on Hi38-71 had poorest performance over all aspects of growth and reproduction examined. Difference in number of progenies produced and days to 50% mortality appeared to account for most of the difference observed in the genetic study. The second study estimated genetic parameters for polysora rust resistance in Hi38-71. Hi38-71 exhibited moderately high resistance to polysora rust as well as resistance to com leaf aphid. Generation mean analysis showed that epistatic interactions of [aa] and [dd] along with simple dominance and additive gene effects were involved in controlling resistance in Hi38-71 to polysora rust. It is concluded that polysora resistance breeding cannot be based on selection of a single parent but a hybrid-breeding or reciprocal recurrent selection approach appears justified. The tropical sweet corn inbred, Hi38-71 is a sib line of Hi38 which was bred from a bt-1 conversion of AA8sh2. AA8sh2 was studied for its resistance to corn leaf aphid in 1970's in Hawaii and was converted to common rust resistance, Rd1-D which broke down due to evolved racial variation of the pathogen. Hi38-71 is thus of particular value in sweet corn breeding for tropical regions. This is due not only to its resistance to corn leaf aphid and polysora, but to its high sweet corn qualities and generally good combining abilities