Melon Populations Research Articles

Molecular analysis of genetic diversity in melon landraces (Cucumis melo L.) from Myanmar and their relationship with melon germplasm from East and South Asia

Genetic diversity of Myanmar melon was evaluated by analysis of 27 RAPD markers and morphological characters using 41 accessions of melon landraces of which 36 accessions were small-seed type. The gene diversity was 0.239, higher than for group Conomon from East Asia and equivalent to Indian melon populations. Melon accessions were classified into six major clusters. The largest cluster IV comprised mainly group Conomon which was closely related to cluster V consisting of mainly group Agrestis. Most of the accessions of group Cantalupensis were grouped into clusters II or VII and were distantly related to groups Conomon and Agrestis. The genetic relationship to melon accessions from neighboring countries was analyzed. The 24 accessions of clusters IV and V were mostly clustered together with small-seed type melon of India, but the 14 accessions of clusters VI and VII were mostly clustered together with large-seed type melon of India. These results indicated that the genetic diversity of Indian melon is conserved in Myanmar. Genetic introgression among melon groups through spontaneous hybridization was also indicated and was considered important to maintain or increase the genetic diversity in Myanmar.

A consensus linkage map identifies genomic regions controlling fruit maturity and beta-carotene-associated flesh color in melon (Cucumis melo L.)

The nutritional value and yield potential of US Western Shipping melon (USWS; Cucumis melo L.) could be improved through the introgression of genes for early fruit maturity (FM) and the enhancement of the quantity of beta-carotene (QbetaC) in fruit mesocarp (i.e., flesh color). Therefore, a set of 116 F(3) families derived from the monoecious, early FM Chinese line 'Q 3-2-2' (no beta-carotene, white mesocarp) and the andromonoecious, late FM USWS line 'Top Mark' (possessing beta-carotene, orange mesocarp) were examined during 2 years in Wisconsin, USA to identify quantitative trait loci (QTL) associated with FM and QbetaC. A 171-point F(2-3) based map was constructed and used for QTL analysis. Three QTL associated with QbetaC were detected, which explained a significant portion of the observed phenotypic variation (flesh color; R (2) = 4.0-50.0%). The map position of one QTL (beta-carM.E.9.1) was uniformly aligned with one carotenoid-related gene (Orange gene), suggesting its likely role in QbetaC in this melon population and putative relationship with the melon white flesh (wf) gene. Two major (FM.6.1 and FM.11.1; R (2) >or= 20%) and one minor QTL (FM.2.1; R (2) = 8%) were found to be associated with FM. This map was then merged with a previous recombinant inbred line (RIL)-based map used to identify seven QTL associated with QbetaC in melon fruit. This consensus map [300 molecular markers (187 co-dominant melon and 14 interspecific; 10 LG)] provides a framework for the further dissection and cloning of published QTL, which will consequently lead to more effective trait introgression in melon.

Peat in the inoculation medium induces fusarium susceptibility in melons

AbstractThe effect of peat moss on fusarium wilt of melon (Cucumis melo L.) was studied in order to improve the selection process of resistant melons during breeding programmes. Disease symptoms were evident earlier and disease progress was faster in seedlings that were transplanted to peat following inoculation than in those transplanted to sand. The resistant breeding line used as a control did not show any wilt symptoms in either medium. Mixing the peat with sand or perlite reduced the disease development rate and the final disease incidence. The effects of peat and sand on disease progress were evaluated with two segregating melon populations in which the expected susceptible : resistant ratio was 25 : 75. In both populations, disease incidence was higher in the peat, which enables breeders to identify resistant plants and to lower the risk of using escapees as resistant plants. The mechanism of disease enhancement may include both biotic and abiotic components. There is an indication that peat induces plant susceptibility before inoculation. Melon seedlings germinated in peat and transplanted into sand exhibited significantly greater wilt incidence than those that germinated in sand and were transplanted into sand following the inoculation. Disease progress in sterile peat was significantly slower than that in non‐sterile peat, which suggests the possible involvement of microbial activity.

Molecular authentication of three Italian melon accessions by ARMS-PCR and ITS1 (internal transcribed spacer 1) secondary structure prediction

Genetic assessment was carried out on three Italian melon accessions by sequence and structural analysis of the internal transcribed spacer 1 (ITS1) from three populations belonging to two Cucumis melo L. varieties (madras and tendral). Alignment of the 18S-5.8S-26S sequences from three melon accessions showed that there were three single-nucleotide polymorphisms (SNPs) and one short insertion-deletion (indel) at the 5'end ITS1. An amplification refractory mutation system (ARMS)-PCR-based analysis was successfully applied to the SNP markers of the ITS1 sequences for the fingerprinting analysis of three melon populations. Secondary structure models for each ITS1 were derived. The prediction of ITS1 RNA secondary structure from each accession was improved by detecting key functional elements shared by all sequences in the alignments. Our results demonstrated that the ITS1secondary structure models can be used to improve the preliminary genetic assessment of the three melon accessions, suggesting a new tool in plant fingerprinting analysis.

Screening of melon populations for resistance to Didymella bryoniae in greenhouse and plastic tunnel conditions

Studies were carried out to evaluate melon populations for resistance to Gummy Stem Blight, caused by Didymella bryoniae for use in breeding programs under greenhouse and plastic tunnel conditions. Were evaluated reactions of half-sib populations of PI 140471 and Anô nº 2 had as with susceptible check Eldorado 300. Plants were inoculated 45 days for needle prickling followed by application of 0.05 ml of 5.0 x 10(5) spores/ml suspension in axis of third and fourth true leaves.Resistance evaluation was made after 90 days of age using a scale varying one to five. PI 140471 and Anô nº 2 progenies were found superior and differed significantly with the checker Eldorado 300 for the F Test. Anô nº 2 possessing multiple resistance to diseases and desirable commercial characteristics, constituted the best resistance source to be used in breeding programs.

The origin and genetic affinities of wild populations of melon (Cucumis melo, Cucurbitaceae) in North America

The origins of wild melon (Cucumis melo) populations in the New World have been in question since their initial description in the mid-nineteenth century by Charles Naudin. Typically, these populations have been assumed to represent escaped forms of cultivated vars. chito or dudaim, and have been labelled accordingly, or more rarely as var. agrestis. To clarify the origins of New World melons, North American, chito, and dudaim accessions were studied with respect to 45 quantitative and 10 qualitative morphological and physiological characters. Also collected were RAPD and SSR data for 42 North American populations, 10 cultivar accessions of vars. chito and dudaim, 10 other small-fruited Old World accessions, and 4 other varieties of C. melo – vars. conomon, flexuosus, inodorus, and cantalupensis. All data revealed that New World populations are distinct, and should be classified as ssp. agrestis var. texanus Naudin. This variety showed the greatest genetic affinities to var. chito and to cultivars from Eastern Asia, including var. conomon.