Cucurbit Genetics Cooperative Report 14:29-31 (article 11) 1991
Preliminary Studies on Cucumis sativus var. xishuangbannanesis
S. L. Yang, H. Pu, P. Y. Liu and Terrence W. Walters
Department of Horticulture, Southwest Agricultural University, Bei-bei, Chong-qing Si-chuan, P. R. China 630716 (first, second and third authors); Fairchild Tropical Garden, 11935 Old Cutler Road, Miami, FL 33156 (fourth author)
Called "Da huang kua" (big cucumber) or "Shan huang kua" (mountain cucumber) by the local residents of the national minority in Yunnan, China, Cucumis sativus L. var. xishuangbannanesis Qi et Yuan, had not been brought to the horticulturist's attention until the Study Group of Vegetable Germplasm Resources investigated crop cultivars of the Yunnan province in 1979 and 1980 (1). This variety occurs in the mountain areas of Xi-shuang-ban-na Autonomous Region (southern Yunnan Province), where the fruits are eaten boiled or raw during different stages of maturity.
Cucumis sativus var. xishuangbannanesis (hereafter referred to as the Xishuangbanna gourd) is variable in fruit shape and rind color. The length: diameter ratio is between 1 and 4, a shorter ratio than that of the typical trellis cucumber, which ranges from 4 to 10. The fruits are round or square in shape, with ash or milky-white colored rind (Fig. 1). Cultivars of the Xishuangbanna gourd have been divided into six cultivar groups by Qi and Yuan (3). The diameter of the round fruited cultivars reaches 46 mm. Fruits, which typically have three to five ventricles, are whitish-green when immature. The orange flesh and placenta of mature fruits darkens from the rind to the placenta with age. Weight of a single fruit averages 2 to 3 kg and contains upwards of 1000 seeds. Based on these characteristics, the Xishuangbanna gourd was originally thought to be variety of C. melo L. (1). However, the flavor of the flesh is similar to that of the common cultivated cucumber (C. sativus).
Fig. 1. Fruits of cucumber (L) and Xishuangbanna gourd (R) showing seedcell.
Xishuangbanna gourd is cultivated in mountain regions in south Yunnan, China at 800 to 1200 m elevation. Plants are usually intercropped with dry rice without trellis support. Seed germination to fruit harvest takes approximately six to seven months. Seeds are sown in April, and fruits harvested in September or October. Plants are vigorous and produce a large quantity of fruits. The raw flesh of the fruit has an excellent taste. Often, mature fruits are stored until the following February by the Hani and Dai people for the Chinese Spring Festival. The local people typically eat fruits raw. Xishuangbanna gourd is considered one of the most important off-season vegetables in the region.
Crosses between the Xishuangbanna gourd and the cultivars C. melo have never succeeded. However, crosses between the Xishuangbanna gourd and different Chinese cultivars of the cultivated cucumber have produced viable seed. The resulting plants of the F1 generation from crosses of the Xishuangbanna gourd and cultivars of cucumber show some degree of heterosis in terms of growth habit. In addition, the frequency of pistillate flowers was reduced reduced, and the length : diameter ratio was smaller than that of a typical cucumber. The orange-colored flesh, a distinctive character of the Xishuangbanna gourd, was transmitted to plants of the F1 generation, suggesting the gene controlling flesh color is dominate. The recessive gene yf reported as controlling orange flesh in the cucumber (2) appears not to be involved in controlling flesh color in the Xishuangbanna gourd.
Culture experiments in Beijing and Chong-ging indicate the Xishuangbanna gourd is difficult to bring into flower in temperate climates, and fruit set is low. these experiments suggest Xishuangbanna gourd requires a warm, humid environment for successful fruit set. The ecological requirements of the Xishuangbanna gourd are similar to that of C. sativus var. sikkimensis Hooker and C. sativus var. hardwickii Kitamura. These cultural requirements are believed to be primitive traits of the domesticated cucumber.
The patterns of peroxidase zymograms obtained from the Xishuangbanna gourd are similar to those of the common cultivars of cucumber and differ from those of C. melo (3). The chromosome number of the Xishuangbanna gourd is identical to that of other cucumber cultivars (2n = 14) and differs from C. melo (2n = 24). However, the karyotype of the Xishuangbanna gourd is different from the cultivated cucumber, with shorter chromosomes in the Xishuangbanna gourd. All seven pairs of chromosomes of both the Xishuangbanna gourd and cucumbers are metacentric, while C. melo chromosomes are mainly submetacentric. A satellite exists in the chromosomes of the cucumber, but is absent from Xishuangbanna gourd.
The primary gene center for the domestication of the cucumber is thought to be the southern Himalaya Mountains in the region of western India, Nepal, Bhutan and Burma (5). The Xishaung-ban-na Autonomous Region is located in the southern portion of Yunnan Province (latitude 20°10' to 23°40'; longitude 99°55' to 101°51'), and has a tropical (warm, humid) climate throughout the year. Thirty percent of vegetation of the region is tropical rain forest where C. callosus (Rottl.) Cogn. and C. hystrix Chakr (4; Yang, personal observation) can be found.
In conclusion, based on karyology, hybridization, and morphological studies, the Xishuangbanna gourd should be considered a variety of C. sativus. The center of origin of the cucumber should be expanded to include the Xishuangbanna region of China. Future studies are planned to examine the relationship between the Xishuangbanna gourd and C. melo.
Acknowledgements. We would like to express our appreciation of Professor C. Z. Qi (Chinese Academy of Agricultural Science) for supplying germplasm for our studies.
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