Research Of Pyramiding Two Gummy Stem Blight Resistance Genes Into Melon (Cucumis Melo L.)

Gummy stem blight is a disease caused by Didymella bryoniae (Auersw.), which is one soil-borne fungal spore. It can cause harm to melon (C. melo L.), cucumber (C. sativus L.), cantaloupe (C. melo ssp. melo), watermelon(Citrullus vulgaris SCHRAD.), etc. at least 12 genera and 23 kinds of cucurbit. The loss of melon yielding caused by gummy stem blight in China and the world become more serious every day, especially in the cultivation facility. The breeding and development of resistant cultivars carrying major resistance (R) genes have been the most effective and economical strategy to control GSB disease to have a neutral effect on the environment. However, the melon varieties that carry a single GSB resistance gene might be reduced or even lost their resistance owes to the abundant variation of the D. bryoniae isolates. Cultivating melon varieties pyramided multiple GSB resistance genes is an effective way to broad spectrum and increase duration of the resistance. In this study, we used single-gene resistance sources to obtain genes pyramided sources. The resistance of genes pyramided had been significantly improved. Then we got one steady genes pyramided source using 145-471 F1 continuous self-polinated. At the same time,’Baipicui’, one muskmelon cultivar, hybrided to 145-398, and then twice backcross. At last, we obtained one commodity good melon line. Specific studies as follows:1. Pyramiding of GSB resistance genes in melon (C. melo L.) and expression analysis of their defense genesWe obtained eight materials pyramided two GSB resistance genes through the crosses of five single resistance gene sources PI140471, PI157082, PI511890, PI482398, PI420145. Seedlings were inoculated with gradient spores concentration of D. bryoniae. The results showed that the resistance of genes pyramided materials 890-398 (PI511890xPI482398) and 145-471 (PI420145 xPI 140471) improved significantly. The expression peaks of PAL, APX, CHT gene in 890-398 were higher or earlier than PI420145 and PI511890. This study showed that pyramiding GSB resistance genes could enhance their resistance to GSB. Genes pyramiding materials can be used for pyramiding breeding of melon.2. The Breeding of Genes pyramided source of melon (C. melo L.) to Gummy stem blight resistance source and related conversion SCAR markerPI420145 and PI140471 are resistance sources to gummy stem blight which containing resistance gene Gsb-6 and Gsb-1. They were hybridized to generate F1 which pyraminding two GSB resistance gene of Gsb-6 and Gsb-1. The F1 were self-polinated three times to steady the pyramiding genes. The genes pyramided individuas each generation were selected with the methods of phenotypic identification and maker-assisted selection. One AFLP marker E-TG/M-CTC200 linked to resistance gene of PI420145 (Gsb-6), and one SSR marker CMCT505 linked to the resistance gene of PI140471 (Gsb-1). The AFLP marker was converted into a SCAR marker, because the AFLP method was expensive and complicate. This study obtained one genes pyramided resistance material. The resistance of pyramided material was higher than the single-gene resistance sources and easy to identify. It can be used as donor parent for pyramiding breeding.3. Pyramiding of Two GSB Resistance Genes into Muskmelon (C melo spp.melo) Cultivar using Marker Assisted SelectionPI482398 and PI420145 are two GSB resistance sources and contain dominant resistance Gsb-4 and Gsb-6 respectively. The donor parent 4598 with pyramided resistance genes was derived from PI420145 and PI482398, and was hybridized with muskmelon ’Baipicui’(a high susceptible cultivar to GSB) to produce BC1 and BC2 populations. The conventional phenotype identification and molecular marker-assisted selection were used to identify the pyramided individuals of F1, BC1 and BC2 populations. Eleven BC2 plants were obtained that contained two GSB resistance genes. Field cultivation demonstrated that individuals carrying both genes Gsb-4 and Gsb-6 had a significantly improved resistance to GSB and an improved fruit quality.