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G. Yelenosky, D. Hutchison, and H. Barrett

Ten-month-old seedlings, grown from seed extracted from 22 individual pummelo [Citrus grandis (L.) Osbeck] × trifoliate orange [Poncirus trifoliata (L.) Raf.] citrus hybrid trees that survived -15C freezes near Monticello, Fla., were cold-acclimated in controlled-environment rooms and freeze-tested at -6.7C for 4 h. Freeze damage to open-pollinated progeny was ranked by the number of uninjured seedlings and percentage of leaves killed and wood dieback. Morphological segregation was not associated with differences in freeze survival, and the dominant trifoliate gene was readily evident. Progeny from one tree, identified as 98-71, are considered the most likely candidates for further study in developing cold-hardy citrus trees.

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Daniel F. Warnock, David W. Davis, and William D. Hutchison

European corn borer, Ostrinia nubilalis Hübner, can severely affect sweet corn quality. Selection techniques in field experiments have improved ear feeding resistance associated with morphological features and/or allelochemicals. The isolation and identification of allelochemicals that detrimentally affect O. nubilalismay improve breeder selection for host plant resistance, thus reducing the need for insecticide application. A laboratory bioassay was used to detect chemical resistance factors in silk and kernel tissues of 10 variously resistant sweet corn genotypes. Ground lyophilized tissue from field-grown plants was added to a nutritionally complete larval diet before infestation with O. nubilalis neonates. Larval weights on a 10-day basis and time to pupation were recorded to estimate larval development. Tissue and genotype main effects affected (P ≤ 0.05) 10-day larval weight and time to pupation. Silk tissue (P ≤ 0.05) reduced 10-day larval weight and increased the time to pupation compared with kernel tissue and the cellulose control, which did not differ. Silk tissue reduced larval weight by 65% and increased time to pupation by 4.0 days compared with the cellulose control. Genotypes variously affected (P ≤ 0.05) larval growth and development, reducing 10-day larval weight up to 51% and increasing the time to pupation up to 4.2 days when comparing the best genotype for each developmental stage with the cellulose control. Silk tissue of some genotypes may contain allelochemicals that decrease the rate of larval growth and development. The status of allelochemical detection in silk tissue will be discussed.

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Daniel F. Warnock, David W. Davis, and William D. Hutchison

European corn borer (ECB), Ostrinia nubilalis Hübner, can severely affect sweet corn quality. Selection techniques in field experiments have improved ear feeding resistance associated with morphological features and/or allelochemicals. A laboratory bioassay was used to detect chemical resistance factors in silk and kernel tissues of 10 variously resistant sweet corn genotypes. When added to a nutritively complete diet, kernel tissue from W182E, MN275, and MN272 decreased (P ≤ 0.05) 10-day larval weight (66.3, 61.7, and 54.5 mg, respectively) while kernel tissue from MG15, MN270, and MN3053 increased (P ≤ 0.05) 10-day larval weight (88.3, 81.5, and 80.8 mg, respectively) compared to a cellulose control (71.0 mg). These weight differences, however, were not significant developmentally as 10-day larval maturation (fourth to fifth instar) and pupation time (13.9 to 16.3 days) were similar to the cellulose control (fifth instar and 14.8 days). Silk tissue additions to the diet decreased (P ≤ 0.05) 10-day larval weight compared to the cellulose control (71.0 mg). Larvae exposed to diet containing silk tissue from MN3053, W182E, and `Apache' were lightest (9.1, 8.3, and 7.8 mg, respectively). The heaviest larvae exposed to silk tissue were from diet including `Jubilee' tissue (54.1 mg). Contrary to the instar levels found on the cellulose control, larvae feeding for 10 days on a diet containing silk tissue mainly were at third or early fourth instar excluding larvae exposed to `Jubilee' silk (fourth to fifth instar). For all genotypes, silk additions to diet increased the pupation time compared to kernel additions. Kernel, and especially silk tissue, may contain chemical resistance factors which decrease larval weight and increase developmental time. Identifying sweet corn genotypes with chemical resistance factors may enhance ECB resistance breeding efficiency.

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Fernando A. De Villena, Vincent A. Fritz, Jerry D. Cohen, and William D. Hutchison

Changes in the levels of gluconasturtiin (2-phenylethyl glucosinolate), an aromatic glucosinolate, was used to evaluate the response of ‘Green Rocket’ Chinese cabbage (Brassica campestris ssp. pekinensis L.) to the feeding of three and five cabbage looper (Trichoplusia ni Hübner) larvae per plant. Plants were harvested 0, 10, and 17 days after infestation. The change in gluconasturtiin concentration resulting from decreased light capture from diminished leaf area was also studied. All samples were assayed for gluconasturtiin concentration using high-performance liquid chromatography. The gluconasturtiin concentration of plants subjected to five larvae per plant showed a 59% increase 10 days after infestation compared with noninfested plants. Difference in gluconasturtiin concentration between three and five larvae per plant was nonsignificant. Seventeen days after initial infestation and 7 days after larvae were removed (final harvest), gluconasturtiin concentration did not decrease compared with the previous harvest. Reduced light or leaf area removal did not significantly affect gluconasturtiin concentration.