Resistance to melon vine decline derived fromCucumis melossp.agrestis:genetic analysis of root structure and root response

Melon vine decline is a major soilborne disease that causes severe economic losses around the world. The fungal pathogensMonosporascus cannonballusPollack et Uecker andAcremonium cucurbitacearumAlfaro‐García, W. Gams et J. García‐Jiménez have been reported as the main causal agents of this disease. A relatively high level of resistance has been reported inCucumis meloL. ssp.agrestis(Naud.) Pangalo in the Asiatic accession Pat 81. Although specific resistance mechanisms controlling pathogen‐induced root lesions have been characterized in Pat 81, the development of a vigorous and branched root system can also appreciably increase its tolerance to vine collapse. The genetics of root traits related to root vigour and structure were studied in the progeny derived from a cross between Pat 81 and the highly susceptible cultivar ‘Piñonet’ market class ‘Piel de Sapo’(C. meloL. ssp.melo).The inheritance of specific resistance to soilborne fungi was also studied by analysing root response to inoculation employing naturally infested soil. Estimates of the broad‐(H) and narrow‐sense (h2) heritabilities indicated that the majority of the variation for lesion resistance in lateral and fine roots, in the root weight, root length, and the root surface area could be explained by additive effects, whereas dominance is important in plant biomass and resistance to lesions in hypocotyls. Selection for improved root systems conferring resistance and tolerance to vine decline was successfully conducted in BC1progeny derived from a Pat 81 בPiñonet’ mating. Moderate values of heritabilities (0.03–0.76) suggest that breeding strategies that combine family and individual selection could enhance genetic progress. As some of the traits analysed exhibited heterosis, breeding methods directed towards recovering hybrid vigour may increase gain from selection.