Assessing common bean genotypes for resistance to Diabrotica speciosa (Coleoptera: Chrysomelidae).

Diabrotica speciosa (Germar) (Coleoptera: Chrysomelidae) is a major pest of common bean (Phaseolus vulgaris L.; Fabales: Fabaceae), and adults can defoliate plants during the whole crop cycle. This study was conducted to evaluate the resistance to D. speciosa in 16 common bean genotypes (14 landraces and 2 cultivars), through three different experiments. In the laboratory, choice and no-choice feeding tests were performed to evaluate the percentage of leaf consumption. In the greenhouse, plant height, numbers of leaves, percentage of injured leaves, percentage of injury per leaf, weight of seeds, and D. speciosa survival were evaluated. Furthermore, trichome density, levels of peroxidase (POD), superoxide dismutase (SOD), and protein content in common bean leaves were assessed. In the laboratory, the genotypes Chumbinho Branco, Dobalde, Manteigado, IPR Tuiuiú, and 90D Mouro were the least consumed by D. speciosa. In the greenhouse, the genotypes Dobalde, Manteigado, and IPR Tuiuiú expressed tolerance to the pest, which was associated with a higher plant height and/or unchanged POD and SOD levels and protein content following insect feeding, and no reduction in seed production. The landrace 90D Mouro exhibited antixenosis and tolerance to D. speciosa, observed as a lower leaf injury, higher trichome density, lower protein contents, higher SOD level and no reduction in seed weight. Overall, we have shown that antixenosis and tolerance can help overcome damages resulting from D. speciosa feeding, with emphasis on four common bean genotypes that may be useful in plant breeding programs aimed at controlling D. speciosa in common bean crops.

Resistance of Cowpea Genotypes to Spodoptera frugiperda (Lepidoptera: Noctuidae) and Its Relationship to Resistance-Related Enzymes.

Spodoptera frugiperda (J.E. Smith) can attack cowpea plants (Vigna unguiculata [L.] Walp.) (Fabales: Fabaceae) in any growth stage but attacks primarily in the first days after plant emergence, when the plants are more sensitive to defoliation. This study was carried out to evaluate the resistance to S. frugiperda in six cowpea genotypes, of which four were cultivars (BRS Tapahium, BRS Tumucumaque, Fradinho, and Miranda), and two were landraces (Juti and Nioaque), in three different experiments. In the first experiment, adult emergence, adult weight, adult longevity, larva to adult period, numbers of injured leaves per plant canopy (upper, middle, and lower), and reduction in plant dry matter were assessed. In the second experiment, the oviposition preference of S. frugiperda for the different cowpea genotypes was evaluated under free-choice conditions. In the third experiment, levels of peroxidase (POD), superoxide dismutase (SOD), and protein content in cowpea leaves were assessed. Insects fed on landrace Juti plants showed low adult emergence, yielded a lower fitness index, and caused less plant dry matter reduction. In addition, plants of landrace Juti were less preferred for oviposition. Overall, Juti plants showed higher resistance levels in all three resistance categories and higher levels of POD and SOD in S. frugiperda injured leaves, in addition to a lower protein content. Juti will be tested in field conditions, followed by molecular characterization. This will provide additional information about its potential as an S. frugiperda resistance source in plant breeding programs.