Watermelon Variety Improvement in China

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Cucurbit Genetics Cooperative Report 15:76-79 (article 30) 1992

Xingping Zhang and Bill Rhodes
Department of Horticulture, E-142 Poole Agricultural Center, Clemson University, Clemson, SC 29634-0375

Watermelons have been grown in China for more than 1000 years. Watermelon is one of the most important economic crops, grown in all parts of China except Qinghai, Tibet plateau and some very cold, northern regions. Watermelon acreages increased rapidly in the last ten years to 1,054,200 hectares in 1989. China is number one in watermelon production and consumption.

Because of the special importance of watermelon, China developed a very large watermelon breeding effort in the last few years. Many agricultural universities, colleges and institutes have watermelon breeding programs. The National Watermelon and Sweetmelon Association (NWSA) of the Chinese Society for Horticultural Science (SCHS) organizes at least one national/regional meeting on watermelon breeding and production each year. The CSHS has a journal called Watermelon and Sweetmelon of China edited by NWSA and Zhengzhou Pomology Institute, Chinese Academy of Agricultural Science. These provide a forum for watermelon breeders to present their research and to exchange ideas. We will provide an introduction to recent efforts made by Chinese watermelon research scientists toward watermelon variety improvement.

F1 Hybrid Development

The advantages of F1 hybrids of watermelon were realized in China in the late 1970s and early 1980s. Before that time, commercial watermelon varieties were open pollinated varieties developed in China (e.g. Zaohua’, ‘Xingchen Hong’, ‘Zhongyu 1’ and ‘Zhengzhou 3’) and introduced by Japan (e.g. ‘Asahi Yamato’ and ‘Miyaka’) and the United States (e.g. ‘Sugar Baby’ and ‘Charleston Gray’) as well as local varieties. The first commercial F1 may have been ‘Xiangmi’ which was released by Hunan Academy of Agricultural Science in 1973. However, the first popular F1 hybrid widely grown in the 1980s was ‘Xincheng’. ‘Xincheng’ was a cross between a selection of a Japanese variety (seed parent) and a selection of ‘Charleston Gray’. An F1 hybrid ‘Xin Hong Bao’ from Taiwan, which appears to be a cross between a round, light green fruit and a selection of a ‘Charleston Gray’ type with small seed, has been very popular since 1986. A national group was organized by the NWSA to develop F1 hybrids of the ‘Xin Hong Bao’ type. three F1 hybrids, ‘Luyuan 1’, developed by GuangZhou Pomology Institute, Guangdong; ‘Jubao 1′ released by Hefei Watermelon Research Institute, Anhui; and “Qihong’, developed by Qiqihr Horticultural Institute, Heilongjiang, were recommended after three years’ cooperative trials, to be the alternates for ‘Xin Hong Bao’. More than sixty F1 hybrids were released by Chinese breeders in the last few years. According to the NWSA, the six most popular commercial varieties in 1989 were all F1 hybrids. The American varieties ‘Charleston Gray’, ‘Jubilee’, ‘Crimson Sweet’ and ‘Sugarlee’ are good parents for generating heterosis in Chinese hybrids.

Efforts were also made to investigate new genes which can be used for hybrid seed production and identification of true hybrids. Two different genic male sterile genes exist in China. The male sterile gene ms from G17AB(9) has been inserted into several desirable cultivars and breeding lines and has been used for hybrid seed production by researchers from Shengyang Agricultural Institute, Liaoning. Another male sterile which was found in Xinjiang is less utilized because of the extreme female sterility associated with the male sterility in the homozygous condition. The male sterile mutant, found from a gamma-irradiated line by Professor Jingyi Wu, may be a cytogenetic male sterile (personal communication). The gene nl, for nonlobed leaves (1), has been introduced into several genotypes to be used as a seedling marker for identification of true hybrids. Cultigens with elongate fruit are preferred as paternal parents so that true hybrids can be discerned by the shape of the ovary.

Isozyme markers for hybrid identification were investigated in Northwestern Agricultural University, Shaanxi, in 1985-1986 (8). More protein and isozyme markers related to hybrid identification are being assayed by researchers from Beijing Vegetable Research Center and Zhengzhou Pomology Institute, Chinese Academy of Agricultural Science.

Watermelon disease resistance breeding is a new subject in China. there is no germplasm with high resistance to Fusarium wilt in Chinese varieties (4). Germplasm introduced from Africa demonstrates great resistance, but are too primitive to be used directly (3). Some American varieties – ‘Dixilee’, ‘Sugarlee’, ‘Charleston Gray 133’, ‘Crimson Sweet’ and ‘Calhoun Gray’ – show moderate or high resistance depending on the host and the wilt isolate. Breeders are trying to use American germplasm to make resistant F1 hybrids. However, genetic studies and breeding practices indicate that the inheritance of Fusarium wilt is much more complex than simple dominance and recessiveness. Results from Jiansu Academy of Agricultural Science indicate that resistance is determined by several recessive genes (7).

Anthracnose resistance has not been a specific project in many breeding programs. The Department of Horticulture, Northwestern Agricultural University has had a Master’s Degree program for studies on watermelon anthracnose since 1986. resistant germplasm has been identified. Pathogen differentiation studies are underway.

Watermelon fruit blotch is a new bacterial disease in China (5). Researchers from Qiqihr Horticultural Institute and Qiqihr Teachers University are working on pathogen identification and resistant germplasm screening.

Triploid Watermelon Development

Triploid watermelon production is mainly in Southeast China. Most of the seedless watermelons are marketed in Hong Kong. Many of the popular seedless watermelon cultivars are round, dark green fruit with red flesh. Only in the last few years have breeders become more interested in breeding for triploid hybrid production. Many more diploid than triploid hybrids have been released, but there will be more triploid varieties released in the coming years. Colchicine treatment has been the only method used by Chinese breeders for chromosome doubling. Yunhe Wang and Zingrong Cai reported a dwarf branch less tetraploid recently, which was developed by a series of crosses, selections and finally, chromosome doubling. It is expected that a novel type of dwarf, branch less triploid watermelon will be available in China in the near future.

Mutation Breeding

Gamma-irradiation issued to induce reciprocal translocations to develop diploids with few seeds. This research began in Guangdong Academy of Agricultural Science, Gansu Agricultural University and Northwestern Agricultural University in the late 1970s (2). In many genotypes, high frequency reciprocal translocations can be induced by using 50 kr for seed irradiation and 3 kr for pollen irradiation. Individuals with 55 percent or lower viable pollen from the M0 (seed) generation or M1 (pollen) generation were selected for cytological testing and selfing. Several chromosome translocation lines are being evaluated in China.

Irradiation can induce various mutations in watermelon. Researchers from Lanzhou Watermelon and Sweetmelon Institute reported an extremely small seed line 91.5H/309, with a weight of 4.5 g/1000 seeds, selected from gamma-irradiated r23X Jubilee M9 population. This line is being used as the paternal parent to produce triploid hybrids. Professor Mingzhou Wu noticed a glabrous mutant from gamma-irradiated population, but she was unable to get seed from the mutant. Professor Jingyi Wu got a male sterile mutant from gamma-irradiated germplasm which may be a cytogenetic male sterile because 100% of a testcross population was male sterile (personal communication).

Application of In Vitro Culture

Successful anther culture has been reported in China in many crops. The only successful watermelon anther culture was reported by Xue, et al. (6). Even though the frequency was low, they did get haploid and then dihaploid watermelon plants from culture. Anthers at the uninucleate stage, 5.0 mm in diameter and flower buds with an obvious corolla were harvested. Calli were induced on MS salts plus 2 ppm BA, 2ppm Kn, 3% sucrose and 0.6-0.7% agar at pH 5.8. Organogenesis was obtained by culturing the hard nodular callus on MS salts plus agar, 5-10 ppm GA3 4 ppm BA, 30-40 ppm adenine and 500 ppm lactalbumin hydrolysate. Differentiated organogenesis and shoot development occurred on agar-based medium with MS salts and 2 ppm triaconital. roots were induced on agar-based medium with 1/2 MS salts and 0.2 ppm IBA, 1 ppm IAA and 1.5% sucrose at pH 5.7.

Efforts toward micropropagation of triploids and chromosome translocation diploid stocks have been made by several labs. Transplanting of triploid watermelon is not yet competitive with direct seeding in China because of the low cost of seed.

Literature Cited

  1. Henderson, W. 1991. Gene list for watermelon. CGC Report 14:129-137.
  2. Wang, Ming et al. 1988. Breeding a few seed/seedless watermelon via chromosome reciprocal translocation induced by gamma ray. CGC Report 11:60-63.
  3. Wang, Ming and Xingping Zhang. 1988. Evaluation and utilization of the valuable Africa watermelon germplasm. Fruit Science 5(3):109-115 (China).
  4. Wang, Ming and Xian Zhang. 1988. Studies on watermelon germplasm sources’ resistance to Fusarium wilt disease at the seedling stage. CGC Report 11:68.
  5. Want, Ming and Li Lu. 1989. Studies on antracnose resistance of watermelon germplasm at the seedling stage. C.E. Thomas (ed.). 1989. Proceeding of Cucurbitaceae 89: Evaluation and Enhancement of Cucurbit Germplasm. pp 154-156.
  6. Xue, G.R., W.Y. Yu and K.W. Fei. 1989. Watermalon plants derived by in vitro anther culture. Pomology Research Institute, Chinese Academy of Agricultural Science, Xingcheng, Lianong, PRC.
  7. Yu, Li and Ranfang Xu. 1991. Preliminary reports on genetic studies on Fusarium wilt resistance in watermelon. National Conference of Watermelon and Sweetmelon Breeding. Urumqi, Xinjiang, August 12 – 16.
  8. Zhang, Zingping and Ming Wang, 1989. Isozyme analysis of F1 hybrids and their parents in watermelon (Citrullus lanatus). Fruit Science 6(2):97-102 (China).
  9. Zhang, Xingping and Ming Wang. 1990. A genetic male-sterile (ms) in watermelon from China. CGC Report 13:45-46.
  10. Zhang, Xingping and Ming Wang. 1990. Identification of watermelon cultivars resistant to Fusarium oxysporum f. niveum isolates collected in different melon production areas in China. Abstracts of 23rd International Congress, 1990.
  11. Zhang, Xingping and B.B. Rhodes. 1990. A new destructive bacterial disease – watermelon fruit blotch. Watermelon and sweetmelon of China. pp 44-46.