Trichomes and Allelochemicals in Tomato Genotypes Have Antagonistic Effects Upon Behavior and Biology of Tetranychus urticae.

Tomato genotypes selected for their high foliar zingiberene (ZGB) contents in a segregating F2 population were assessed to determine their effect on behavior and biology of Tetranychus urticae Koch, the putative resistance mechanisms involved and the role of trichomes on that resistance. Genotypes with contrasting ZGB content (RVTZ-09 = low ZGB, RVTZ-79 = high ZGB, RVTZ-142 = high ZGB, and RVTZ-331 = high ZGB) were selected from an interspecific cross between wild S. habrochaites var. hirsutum accession PI-127826 (high ZGB content and resistant to mites) and S. lycopersicum cv. Redenção (low ZGB content and susceptible to mites). To determine the effect of these genotypes on mite behavior and biology, free- and no-choice tests, as well as biological studies were performed. Types and densities of trichomes on the foliar surface and their correlation with ZGB contents was determined. Genotypes rich in ZGB (RVTZ-79, RVTZ-142, and RVTZ-331) presented a high number of types IV and VI glandular trichomes, and both type IV and VI densities were positively correlated with ZGB content. In the free-choice test, T. urticae showed a high preference toward S. lycopersicum cv. Redenção and the genotype RVTZ-09 (low ZGB content), whereas, genotypes with high ZBG content were less preferred. Moreover, on high ZGB genotypes, increase in the egg incubation period and in total mortality of nymphs, and decrease of fecundity rate were observed, indicating deleterious effects in mite biology. Results indicated that high ZGB/high glandular trichome densities genotypes present both non-preference and antibiosis mechanisms of resistance to the mite.

Inheritance of parthenocarpy in summer squash (Cucurbita pepo L.).

The inheritance of the tendency to set parthenocarpic fruit in the summer squash (Cucurbita pepo L.) line Whitaker was studied. Two parental lines, Whitaker (parthenocarpic) and Caserta (non-parthenocarpic), and the F1 and F2 generations and backcrosses to both parents were tested. The parthenocarpic tendency of individual plants was scored on a scale from 1 (non-parthenocarpic fruit) to 5 (parthenocarpic fruit). The Whitaker line produced parthenocarpic fruit and had a mean score of 4.2, whereas Caserta did not set parthenocarpic fruit and had a score of 1.55. The heritability estimates indicated that genetic gains from selection were feasible. The additive-dominant model showed a good fit, with epistasis being negligible or nonexistent. The hypothesis of monogenic inheritance with incomplete dominance was not rejected within the degree of dominance range from 0.2 to 0.5. These results indicate that parthenocarpy is controlled by a single locus, with incomplete dominance in the direction of parthenocarpic expression.

Correlations between symptoms and DAS - ELISA values in two sources of resistance against tomato spotted wilt virus

The commercial tomato, "Lycopersicon esculentum", cultivars Ângela Gigante I-5100 and Santa Clara (tsopovirus susceptible), the Stevens cultivar, lines and experimental hybrids (tospovirus resistant), were used : a) to evaluate two sources of resistance to tospoviruses in tomato (one from "L. esculentum"/Rey de Los Tempranos, and another one from "L. peruvianum"/Stevens); and b) to verify statistically significant correlation between virus concentration determined through DAS-ELISA and symptomatology. In the Ângela GiganteI-5100 and the Santa Clara cultivars, the correlation coefficient was highly significant and the symptom average level was high, showing that in susceptible cultivars the symptom evolution is related to the virus multiplication in the plant. As for the TOM 547 and TOM 556 lines (background of Ângela Gigante I-5100 and Santa Clara, respectively), there was no statistical correlation between the symptoms and the viral particule concentration. Plants with light virus symptoms showed high absorbance values. Consequently we may assume that the resistance with 'Rey de Los Tempranos' background may be of the tolerant kind because the high virus concentration found does not necessarily relate to a high level symptoms. In the lines BPX320E 3902-01, BPX320E 3905 and BPX320F 7902 (both with Santa Clara background) only few plants showed symptoms, which can be explained by incomplete penetrance of Sw-5 gene. In the case of non-symptomatic plants, the diagnosis using DAS-ELISA revealed negative results. That outcome indicates that in some materials, where resistance is obtained from "L. peruvianum", the virus multiplication in the tissues seemed not be present.