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Feishi Luan and Zhanyong Sun

The purpose of this study was to analyze the genetic relationship by using morphological, biochemical, and molecular markers. Sixty accessions of green bean [Phaseolusvulgaris (L.)], including 43 from North China, 13 from the International Center for Tropic Agriculture, and four from Poland, were collected and divided into three groups: cultivated determinate (35), cultivated indeterminate (12), and semi-wild determinate (13). Dendrograms were constructed based on the genetic similarity and distance analysis of these 60 accessions by using biological characters, allozyme, and random amplified polymorphic DNA (RAPD) markers. The 60 accessions were classified into two groups based on the genetic relationship examined in their biological characters. The cultivated indeterminate formed one group, and cultivated determinate and semi-wild determinate belonged to another group. Ten allozymes with 25 polymorphic loci divided the 60 accessions into nine groups, i.e., five groups for cultivated determinate, two groups for cultivated indeterminate, and two groups for semi-wild determinate. Twenty-nine RAPD markers with 314 polymorphic loci divided the 60 accessions into 13 groups, i.e., nine groups for cultivated determinate, three groups for cultivated indeterminate, and one group for semi-wild determinate. The average genetic similarities and genetic distance of intra-group and inter-groups were 0.81 and 0.75, and 0.19 and 0.24, respectively. Ten bands were characterized as specifically associated with cultivated determinate, one band specific for cultivated indeterminate, and one band for semi-wild. These biochemical and molecular markers provided more information than morphological markers. Allozyme and RAPD markers can be used as an available tool to exploit green bean germplasm in the future.

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Yuhe Li, Feishi Luan and Hongyan Ma

This experiment researched the effects of supplementary light on cucumber [Cucumissativus(L.)] seedling growth and some physiological characteristics under the same temperature. The purpose was to afford basic light condition control of cucumber cultivation in a greenhouse during winter to spring. Two cucumber cultivars, No. 3 `Jinchun' (greenhouse cultivar) and No. 7 `Longzahuang' (open field cultivar), were transplanted with supplementary light at different intensities. The experimental results indicate that plant height, leaf area, and stem diameter of cucumber seedlings were significantly increased with increasing intensity of supplementary light. Supplementary light at the cucumber seedling stage led to the increase of chlorophyll content, soluble sugar content, protein content, and CAT activity. At the same time, reduction in POD activity and MDA content with increasing levels of supplementary light was found. In addition, cells of supplementary light treatments have more chloroplasts, grana, and starch grains. Chloroplast growth of supplementary light treatments was better than CK. The grana lamella was arranged in order and its structure was clear. These results show that supplementary light could improve the growth of seedling plants, alleviate the damage of membrane lipid peroxidation, and facilitate chloroplast growth. The effects of supplementary light on the two cultivars were the same, but their extent was different. Effects on No. 7 Longzahuang were more significant than those on No. 3 Jinchun.

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Yunyan Sheng, Feishi Luan, Faxing Zhang and Angela R. Davis

Genetic diversity among 95 watermelon (Citrullus lanatus) ecotypes was evaluated and compared with representative Chinese, American, Japanese, and Russian watermelon cultigens, landraces, and a wild watermelon relative (Trichosanthes kirilowii). Open-pollinated, hybrid, and inbred lines were included for most of the ecotypes and are hereafter collectively referred to as cultigens unless an ecotype group is being discussed. Morphological characteristics (including days to flower, female to male flower ratio, branch number, fruit length and diameter ratio, fruit soluble solid content, fruit yield, and simple sequence repeat (SSR) markers were used to estimate genetic diversity. Of 398 watermelon primer pairs tested, 9.5% (38) produced polymerase chain reaction amplicons in watermelon. Of these 38 primer pairs, the average number of polymorphic bands among the 96 cultigens was 2.4, even with 12 primer pairs demonstrating monomorphic banding patterns. Based on the SSR data, the genetic similarity coefficients were calculated and a dendrogram constructed. All cultigens were clustered to six groups. The wild species and landraces formed distant clusters from the cultivated watermelon. The genetic similarity coefficients within the Chinese cultigens ranged from 0.37 to 0.99, but except for a wild relative to watermelon, most cultigens were closely related. The genetic distance among non-Chinese cultigens ranged from 0.67 to 0.91 with an average of 0.88. When combined morphological traits and molecular traits were assessed, Russian and U.S. fruit were more genetically similar to each other than to Chinese and Japanese cultigens. Crossing Russian and/or U.S. cultigens with Chinese or Japanese cultigens should thus improve genetic diversity and introduce new traits for the resulting watermelon cultigens.

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Nan Wang, Shi Liu, Peng Gao, Feishi Luan and Angela R. Davis

Citrullus lanatus (watermelon) is an excellent daily source of dietary lycopene and β-carotene. To investigate the transcriptional regulation of carotenoid biosynthesis genes relative to lycopene and β-carotene accumulation in watermelon fruit, six watermelon accessions with different flesh colors were examined in this study: white-fleshed PI 459074, pale-yellow-fleshed ‘Cream of Saskatchewan’, light-pink-fleshed PI 482255, orange-yellow-fleshed ‘WM-Clr-1’, and red-fleshed ‘LSW177’ and ‘MSW28’. The expression patterns of eight genes (PSY1, PSY2, PDS, ZDS, CRTISO, LCYB, NCED1, and NCED7) involved in lycopene and β-carotene biosynthesis and biodegradation were analyzed. The results confirmed the accumulation of large quantities of lycopene in red-fleshed ‘LSW177’ and ‘MSW28’, reflecting the elevated expression of PSY1 and the low transcriptional expression of NCED1. The relative expression levels of NCED1 likely play an important role in the color development of the light-pink-fleshed PI 482255, whereas the reduced transcriptional expression of PSY1 and the increased expression of NCED1 appear to be the main factors contributing to the formation of white flesh in the fruit of PI 459074. Low transcriptional expression of PSY1 results in the pale-yellow flesh of the ‘Cream of Saskatchewan’ fruit.

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Taifeng Zhang, Jiajun Liu, Shi Liu, Zhuo Ding, Feishi Luan and Peng Gao

Short internode length (SIL) is one of the most commercially and important traits in melon varieties (Cucumis melo L.). SIL can result in a compact vining type that promotes concentrated fruit in high-density crops, leading to greater use of light resources for photosynthesis and greater yield per unit area. In our study, two parental melon lines ‘M1-32’ (P1, standard vine) and ‘X090’ (P2, short internodes), and their F1, F2, BC1P1, and BC1P2 progenies were evaluated after being grown in plastic greenhouse conditions in 2017 and 2018. Main stem length (MSL) and internode length (IL) of six melon generations indicated that a single recessive gene (MD7) controlled dwarfism in the ‘X090’ melon line. Whole-genome analysis revealed a genomic region harboring the candidate dwarfism gene on chromosome 7. Six polymorphic cleaved amplified polymorphic sequence (CAPS) markers from chromosome 7 were used to construct a genetic linkage that spanned 30.28 cM. The melon dwarfing locus MD7 responsible for SIL was positioned between markers M7-4 and M7-5, with 3.16 cM of flanking distance. The CAPS markers M7-4 and M7-5 developed have the potential to accelerate the development of dwarf melon varieties, especially in situations when dwarf genotypes are an important breeding goal using marker-assisted selection.