Resistance to the Pink Stem Borer in Twenty Exotic Maize Populations Under Natural and Artificial Infestation Conditions

Twenty exotic maize populations with different genetic background representing different geographical zones were obtained from Maize Gene Bank of Maize Res. Dept., Field Crops Res. Inst. (FCRI), Agric. Res. Center (ARC), Egypt. They were evaluated in 2011 to determine their level of resistance to the pink stem borer Sesamia cretica under natural infestation at Nubaria, Gemmeiza and Sakha Agric. Res. Stn. and under artificial infestation at Giza Agric. Res. Stn. A Randomized Complete Block Design was used. Evaluation trials under natural infestation were planted in the early summer (April) while under artificial infestation planting took place in the normal growing season (May). Three resistance expressing traits, i.e. percentage of infested plants (IP), percentage of plants with dead hearts (DH) and intensity of damage (ID) were used to evaluate the level of resistance in the twenty populations. Five-classes rating scale was developed to evaluate the intensity of damage caused by larvae of S. cretica. Results showed that, populations Tamps. 23 and Antigua have relatively good level of resistance to infestation by larvae of S. cretica. The two populations could be integrated into maize breeding programs which aim at developing hybrids resistant to S. cretica. Highly significant correlation coefficients were found among pairs of the three resistance expressing traits under artificial infestation. Correlation between results under natural and artificial infestation for the three studied traits showed low to moderate correlation which indicated that, for precise results on the level of resistance to S. cretica, evaluation should be made under artificial infestation conditions. In addition, exotic germplasm should be considered as a source for resistance genes in breeding programs for insect-pest resistance.