Chinese Hami melon consists of the varieties cassaba, chandalak, ameri, and zard. To show their genetic diversity, 120 melon accessions, including 24 accessions of Hami melon, were analyzed using molecular markers of nuclear and cytoplasmic genomes. All Hami melon accessions were classified as the large-seed type with seed length longer than 9 mm, like US and Spanish Inodorus melon. Conomon accessions grown in east China were all the smallseed type. Both large-and small-seed types were in landraces from Iran, Afghanistan, Pakistan, and Central Asia. Analysis of an SNP in the PS-ID region (Rpl16-Rpl14) and size polymorphism of ccSSR7 showed that the melon accessions consisted of three chloroplast genome types, that is, maternal lineages. Hami melon accessions were T/338 bp type, which differed from Spanish melon and US Honey Dew (T/333 bp type), indicating a different maternal lineage within group Inodorus. The gene diversity (D), calculated from random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) polymorphism, was 0.476 in 120 melon accessions; the largest diversity was in Central Asian accessions (D = 0.377) but was low for Hami melon accessions (D = 0.243), even though Hami melon has diverse morphological traits, earliness, and shelf life. Reflecting such small genetic diversity, Hami melon accessions of vars. ameri and zard were grouped into cluster II, except for one accession, by the unweighted pair group method and the arithmetic mean (UPGMA) cluster analysis. Variety chandalak with distinct characters, such as early maturing and poor shelf life, was assigned to clusters IV and VI, indicating inter-varietal genetic differentiation within Hami melon. Three accessions from Turkmenistan and Afghanistan, with large seeds and T/338 bp type of chloroplast genome, were classified as cluster II with Hami melon accessions of vars. ameri and zard. We therefore concluded that Hami melon may have been transmitted from the west. The small-seed type melon of group Conomon grown in east China may have been introduced into China independently of Hami melon, because it had the A/338 bp type of the chloroplast genome and was clustered distantly from Hami melon according to nuclear genome analysis.

Genetic diversity among 59 melon landraces from Vietnam was studied by analyzing morphological traits and molecular markers. The morphological characters of the melon landrace fruits were highly diversified. Among the five types of cultivated melon, "Dua le" and "Dua vang" were classified as Conomon var. makuwa, whereas "Dua gang" was classified as Conomon var. conomon, and "Dua bo" was classified as Momordica. However, "Dua thom" could not be classified into a proper group or variety. The gene diversity based on random amplified polymorphic DNA (RAPD) and single sequence repeat analyses was small and equivalent to that of Chinese Conomon. A cluster analysis revealed that "Dua bo", "Dua le", "Dua vang", and "Dua gang" were grouped in cluster II. Clusters III and IV consisted mainly of Conomon accessions from China and Japan. "Dua thom" was classified into cluster V with landraces from Yunnan Province, China. The comparison of a RAPD profile with 291 melon accessions from Africa and Asia clearly showed that "Dua thom" and Yunnanese landraces were closely related with the small-seed type melons from Myanmar, Bangladesh, and northeastern India. The other four types were related closely with Conomon and Agrestis accessions from China, Korea, and Japan, indicating their involvement in the differentiation and establishment of the Conomon group in East Asia.

To understand the genetic diversity and differentiation of Vietnamese melon ( Cucumis melo L.), we collected 64 landraces from the central and southern parts of the country and assessed molecular polymorphism using simple sequence repeat and random amplified polymorphic DNA markers. The Vietnamese melon was divided into seven cultivar groups, namely “Dua le”, “Dua vang”, “Dua bo”, “Dua gang-andromonoecious”, “Dua gang-monoecious”, “Dua thom”, “Montok”, and the weedy-type melon “Dua dai”. Among these, Dua le, Dua vang, Dua bo, and Dua gang-andromonoecious are cultivated on plains and they formed cluster II along with the reference accessions of Conomon and Makuwa. Based on genetic distance, Dua le and Dua vang were regarded as Makuwa and Dua bo and Dua gang-andromonoecious as Conomon. In contrast, Dua thom and Montok are cultivated in highlands, and they formed cluster III along with landraces from the southern and eastern foot of the Himalayas. Dua gang-monoecious which is commonly cultivated in the southern parts of Vietnam, exhibited the greatest genetic diversity, as explained by its possible origin through the hybridization between Dua gang-andromonoecious and Montok. Genetic differences in melon landraces between plains and highlands and hybridization between these two geographical groups have contributed to the enhancement of genetic diversity in Vietnamese melon.

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