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).

Genetic divergence among accessions of melon from traditional agriculture of the Brazilian Northeast.

The genetic divergence of 38 melon accessions from traditional agriculture of the Brazilian Northeast and three commercial hybrids were evaluated using fruit descriptors and microsatellite markers. The melon germplasm belongs to the botanic varieties cantalupensis (19), momordica (7), conomon (4), and inodorus (3), and to eight genotypes that were identified only at the species level. The fruit descriptors evaluated were: number of fruits per plant (NPF), fruit mass (FM; kg), fruit longitudinal diameter (LD; cm), fruit transversal diameter (TD; cm), shape index based on the LD/TD ratio, flesh pulp thickness, cavity thickness (CT; cm), firmness fruit pulp (N), and soluble solids (SS; °Brix). The results showed high variability for all descriptors, especially for NPF, LD, and FM. The grouping analysis based on fruit descriptors produced eight groups without taxonomic criteria. The LD (22.52%), NPF (19.70%), CT (16.13%), and SS (9.57%) characteristics were the descriptors that contributed the most to genotype dissimilarity. The 17 simple sequence repeat polymorphic markers amplified 41 alleles with an average of 2.41 alleles and three genotypes per locus. Some markers presented a high frequency for the main allele. The genetic diversity ranged from 0.07 to 0.60, the observed heterozygosity had very low values, and the mean polymorphism information content was 0.32. Molecular genetic similarity analyses clustered the accessions in 13 groups, also not following taxonomic ranks. There was no association between morphoagronomic and molecular groupings. In conclusion, there was great variability among the accessions and among and within botanic groups.