Mapping quantitative trait loci for fruit traits and powdery mildew resistance in melon (Cucumis melo L.)
Date Issued
2016
Date
2016
Author(s)
Wang, Yu-Hua
Abstract
Melon is a crop of economic importance and the fruit characters determine consumer’s satisfaction and the market value. The genetic information of fruit quality-related characters is a prerequisite for the breeding of high quality melon. Furthermore, powdery mildew is a limiting factor in melon production. To develop new cultivars for stable production of high-quality melons, the pyramiding of genes determining fruit traits and disease resistance is required. Twenty-four inbred lines of different types were screened for genetic diversity using fifteen inter simple sequence repeat (ISSR) primers. These inbred lines were grouped into two clusters based on ISSR markers. One inbred line of each cluster was selected and crossed to create two dependent F2 populations. One is TARI-08874 belonging to Cucumis melo ssp. melo, and another is ‘Bai-li-gua’ belonging to Cucumis melo ssp. agrestis. The combined F2 population containing 484 individuals from the cross of TARI-08874 and ‘Bai-li-gua’ were used to map the quantitative trait loci (QTLs) for fruit-related traits and powdery mildew resistance. The generated linkage map was consisted of twelve major linkage groups (LGs), one minor linkage group, and two unlinked markers, spanning 632.4 cM in total, with an average distance of 8.1 cM between flanking markers. The correlations among eight essential fruit traits were analyzed and the quantitative trait loci (QTL) of fruit were identified over two trials conducted in different period. The evaluated fruit traits include fruit weight, fruit diameter, fruit length, flesh thickness, external color, flesh color, fruit net density and net width. The two parental lines, TARI-08874 (Cucumis melo ssp. melo) and ‘Bai-li-gua’ (C. melo ssp. agrestis) exhibited significant difference in all investigated traits (P < 0.05). There were high correlations among the fruit size-related traits, namely, fruit weight, fruit diameter, fruit length and flesh thickness. The two skin netting traits, netting density and netting width were highly correlated. However, the two coloration characters, external color and flesh color showed no correlation. The combined F2 population developed from TARI-08874 x ‘Bai-li-gua’ cross was used to map the QTLs involved in eight fruit traits over two trials. In total, 21 QTLs were detected, among which eleven were localized to the same positions as those described previously, and ten novel QTLs were detected. Six QTLs were detected in both trials. The results of 10 QTLs identified for fruit size related traits suggested that fruit size was mainly determined by fruit diameter and flesh thickness of which major QTLs were mapped on LG5 and LG11. One QTL for ECOL possessing a high allelic effect, qECOL4 was closely linked with marker CMBR154, suggesting the potential application in marker-assisted breeding. Two QTLs controlling flesh color were positioned in LG5 and LG8, respectively. The fruit netting, a crucial appearance factor in Asian market is an important study focus, in particular netting width. Four QTLs were defined for both netting density and netting width. This is the first report on QTL mapping for netting width. Powdery mildew (Podosphaera xanthii) is a serious disease of melon. Ten melon differentials were used to identify the races in Tainung and Taichung experimental field. Discrepancies in the respones of these differentials revealed that the predominant races existed in the open field were P. xanthii race 1 and race 5 in the two regions, but there were also a few unknown races. The evaluation results on the resistance of fifty-seven melon inbred lines to P. xanthii race 1 and race 5, showed that twenty-four inbred lines were resistant to race 1, while only two inbred lines were resistant to race 5. According to the genetic analysis of the resistant inbred line TARI-08874, the resistance was controlled by a dominant gene. The combined F2 population was also used to map the quantitative trait locus (QTL) for powdery mildew resistance. One major QTL for powdery mildew resistance was detected on LG2 which was closely linked to a simple sequence repeat (SSR) marker CMBR120 identified in a previous study.
Subjects
Cucumis melo
inter simple sequence repeat (ISSR)
simple sequence repeat (SSR)
quantitative trait loci (QTLs)
genetic correlation
fruit size
fruit color
flesh color
fruit netting
Podosphaera xanthii
genetic analysis
quantitative trait locus
Type
thesis
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