New sources of resistance to leafminers (Liriomyza sativae) in melon (Cucumis melo L.) germplasm.

Leafminers (Liriomyza sativae) are the main melon (Cucumis melo L.) pests in Northeast Brazil, which is the main region for the production and export of the fruit in Brazil. Of the integrated management strategies available, genetic resistance is the best method of preventing damage by these insects. The aim of this study was to select sources of resistance to leafminers in melon germplasm. Seven experiments were conducted in the laboratory, field, and greenhouse, with and without choice, using 52 melon accessions and 4 commercial hybrids as controls. Genetic variability among the accessions made it possible to select four new sources of resistance: 'CNPH 11-1072' and 'CNPH 11-1077', because they exhibited lower levels of infestation by the insect (antixenosis); and 'CNPH 00-915(R)' and 'BAGMEL 56(R)', because the pest larvae died soon after beginning to feed on the leaf mesophyll (antibiosis).

What is the influence of ordinary epidermal cells and stomata on the leaf plasticity of coffee plants grown under full-sun and shady conditions?

Stomata are crucial in land plant productivity and survival. In general, with lower irradiance, stomatal and epidermal cell frequency per unit leaf area decreases, whereas guard-cell length or width increases. Nevertheless, the stomatal index is accepted as remaining constant. The aim of this paper to study the influence of ordinary epidermal cells and stomata on leaf plasticity and the influence of these characteristics on stomata density, index, and sizes, in the total number of stomata, as well as the detailed distribution of stomata on a leaf blade. As a result, a highly significant positive correlation (R²(a) = 0.767 p ≤ 0.001) between stomatal index and stomatal density, and with ordinary epidermal cell density (R²(a) = 0.500 p ≤ 0.05), and a highly negative correlation between stomatal index and ordinary epidermal cell area (R²(a) = -0.571 p ≤ 0.001), were obtained. However in no instance was the correlation between stomatal index or stomatal density and stomatal dimensions taken into consideration. The study also indicated that in coffee, the stomatal index was 19.09% in shaded leaves and 20.08% in full-sun leaves. In this sense, variations in the stomatal index by irradiance, its causes and the consequences on plant physiology were discussed.