Seleção de genótipos de meloeiro para obtenção de linhagens com resistência à Didymella bryoniae

Abstract

- Among the diseases that affect the melon crop, the gummy stem blight, caused by Didymella bryoniae, is currently considered the most important and causal agent of substantial losses. In this context, the use of resistant appears as an advisable strategy in the integrated management of the disease. In the process to obtain resistant cultivars, it is necessary primarily to identify reliable sources of resistance and use an appropriate method to effectively evaluate the plant-pathogen interaction; the methodology must be fast, convenient and compatible with the genetic inheritance of this characteristic. Under this viewpoint, the present work had the following objectives: a) evaluation of melon accesses for resistance to D. bryoniae. b) adjustment of methodology, including the appropriate time (days after inoculation) to the evaluate the reaction of melon genotypes to the pathogen; c) estimation of the effects of general combining ability (GCA) and specific combining ability (CEC) in a diallel cross among six lines of muskmelon to provide basic information for their use as parents in breeding programs toward the development of line with resistance to D. bryoniae. The experiments were conducted in the Setor de Olericultura e Plantas Aromático-Medicinais e no Laboratório do Departamento de Fitossanidade, na Faculdade de Ciências Agrárias (UNESP-FCAV) – Câmpus de Jaboticabal. The results regarding the reaction to gummy stem blight identified the access AC-29, C160, Charentais Fom 1, PI 420145, PI 482398 and PI 532830 as resistant to D. bryoniae and thus indicated as important sources of genes for the development of resistant cultivars. Considering the two methods of evaluation and their particularities (expended time, convenience and efficiency), Method II was considered the most indicated to evaluate the resistance reaction; it allows the removal of plants from the humid chamber three days after inoculation. Results from the diallel analysis showed the accesses PI 420145 and PI 482398 with negative and significant estimates of GCA; the crosses JAB-11 x PI 420145, JAB-11 x PI 482398, JAB-20 x PI 140471, JAB-20 x PI 420145 and AB-20 x PI 482398 showed the best estimates of CEC. Negative estimates of both GCA and CEC are in the desirable direction of resistance.