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Trials were conducted in 1997 and 1998 to determine if there is a range of resistance to European corn borer [Ostrinia nubilalis (Hübner)] (ECB) in commercially available processing sweet corn (Zea mays L.). Twelve processing corn cultivars were tested in 1997 and 18 cultivars in 1998. About 40 first instar larvae of colony-reared ECB were used to infest plants in both whorl and silking stages of growth. At harvest, plants infested at the whorl stage were evaluated for numbers of larvae and larval tunnels, and length of larval tunnels. Plants infested at the silking stage were evaluated for number of larvae per ear and were rated for ear damage using a 9-point scale. Resistance rankings among cultivars were consistent between years and between silk- and whorl-infested plants. We conclude that there is a substantial range of resistance already present in processing sweet corn cultivars, and that resistance is probably a combination of both exclusion and suppression of feeding. Our findings have two immediate uses: incorporation into existing IPM programs and incorporation of identifiable resistance bearing cultivars into a long-term breeding program for resistance to ECB in sweet corn.
A replicated greenhouse evaluation of a range of commercial and noncommercial (Capsicum spp.) accessions for resistance to european corn borer (ECB) [Ostrinia nubilalis (Hubner)] was conducted. Percentage of fruit damaged was observed among 29 accessions four weeks after plants were artificially infested with ECB egg masses. Small-fruited peppers generally showed lower levels of damage, while large-fruited peppers were the most susceptible. Genotypes with elongate fruit were less damaged than those with bell-shaped fruit. Resistance to fruit damage was also associated with increasing pungency level, with two notable exceptions. The pungent genotype `Large Red Thick Cayenne' was significantly more susceptible than many of the other pungent accessions tested. The relative susceptibility of this accession may be related to large fruit size. The nonpungent pepper `Corno di Toro' showed significantly lower percent fruit damage than other nonpungent peppers including `Banana Supreme' with roughly similar fruit size, ranking amidst highly pungent peppers such as `Red Scotch Bonnet'. These results confirm that resistance to ECB can be identified in nonpungent Capsicum genotypes and demonstrate that pungency is not always correlated with ECB damage. Reported sources of aphid resistance or tolerance showed good levels of ECB resistance, but interpretation of these results was confounded by the presence of pungency.
A greenhouse screen for resistance to green peach aphid (GPA) [Myzus persicae (Sulzer)] was done using 50 pepper (Capsicum spp.) accessions. There were significant differences among accessions for damage rating, number of aphids per plant and number of aphids per leaf. Leaf pubescence, the basis of a reported nonpreference resistance mechanism to green peach aphid infestation, failed to protect pepper accessions from GPA colonization and damage. Sources of resistance and tolerance to cotton aphid [Aphis gossypi (Glover)] supported high levels of green peach aphid infestation and exhibited considerable damage. Although no accessions provided strong resistance to aphid colonization evident by significantly reduced numbers of aphids, several commercial varieties and sources of virus resistance exhibited strong tolerance to GPA, evident as reduced damage. Tolerant varieties could be an important component in integrated pest management of green peach aphid.