Cucurbit Genetics Cooperative Report 14:5-7 (article
Cucumber Cultivar Improvement in the People's Republic of China
Hongwen Cui and Xingping Zhang
Department of Horticulture, Northwestern Agricultural University, Yangling, Shaanxi, 712100, P.R. China
Cucumber (Cucumis sativus L.) is as important as tomato in vegetable production in China. Cucumber is grown widely throughout the country, especially in North China, where it is the number one summer vegetable. Cucumber is second in area after Chinese cabbage. China is the biggest cucumber producing country in the world, with a total area of 230,000 ha and a total production of 300,000 Mg. The main provinces / cities for cucumber production are Shandong, Beijing, Tianjin, Liaoning, and Shaanxi. Shandong ranks first, with a total area of approximately 25,000 ha. Yields per hectare vary greatly (7 to 100 Mg) because of differences in cultivar, growing season, growing system, and cultivation technique. The highest record is 328,112.5 kg/ha. Because of the favorable climate condition, most of the country's cucumber (80 to 90%) are grown during spring and early summer. A small part of cucumbers are produced during fall and winter in the greenhouse. The objective of this article was to review the work on genetic improvement of cucumber in China.
Cucumber improvement in China. China has a cucumber growing history of 2,000 years (4). Great genetic diversity has developed in the different parts of the country due to both natural and artificial selection. All of the cultigens (cultivars, gene mutant lines, breeding lines) can be classified into two groups, the North China group (so called 'Chinese Long') and the South China group. Each of the groups can be divided into four horticulture types: watering cucumber, staking cucumber, drought tolerant cucumber (usually rain fed) and non-staked cucumber. The former two types are commonly used, and the latter two types are scattered in small quantities. Most of the cucumbers in China are for fresh market, but cucumbers for pickling are also grown. We have no official estimate of the number of cucumber accessions maintained in China, but at least 1,000 are known. Investigations carried out by Shandong Academy of Agricultural Science indicated that there were more than 100 local races of cucumber in the country. However, much excellent germplasm has been unavailable because of lack of proper conservation.
Organized and scientific cultivar improvement was carried out only in the last 40 years, and cucumber breeding has been further improved during the last 20 years. Three important periods are summarized below according to the major work carried out.
Germplasm resource investigation (1949-1963.) The vegetable research staff was organized and equipped in the early 1950s in the scientific units of many provinces and big cities of China. A national vegetable germplasm resource (including cucumber) investigation and collection was carried out in 1955. Some outstanding local cucumber cultivars, e.g. Ningyan Cigua, were found and collected during the national investigation. The collected local cultivars played an important role since they were utilized widely in commercial production. An extensive germplasm investigation of ten important vegetable crops including cucumber, Chinese cabbage, etc., was organized in 1959. More germplasm resources were collected, and some efforts toward asexual gene transfer and F1 hybrid breeding were made during these periods, but there is no successful work reported.
Breeding new cultivars (1964-1979). The program on sexual cross breeding initiated in Tianjin Academy of Agricultural Science in 1964 marked a new epoch of scientific cultivar improvement of cucumber in China. However, only a few researchers and breeders were focused on cucumber breeding in the 1960s. In early 1970s research groups undertaking cucumber improvement were established in almost 20 universities and academies of agricultural science, including Northwestern Agricultural University, Shandong Academy of Agricultural Science, and Beijing Academy of Agricultural Science. Research in these periods was concentrated on breeding new elite cultivars using genetic recombination. Gynoecious line and inbred line development were also included in breeding program (1). F1 hybrid breeding was in consideration or in experiment. Attention was also paid to resistant and high yield cultivar selection because of the increasing severity of diseases.
F1 hybrids with multiple disease resistance (1979-present). A national cucumber breeding group consisting of seven units (e.g. Chinese Academy of Agricultural Science, Northwestern Agricultural University) was organized in 1979. Cooperative programs and breeding objects were made at the annual meeting of the group. This group has been developed in the last eleven years. Up to now, the group covers 22 research institutes and universities or colleges. A National Cucumber Research Association was established in December, 1990 on the basis of the national cucumber breeding group. The association will be helpful for researchers and breeders exchanging their ideas and information, as well as germplasm. Breeding during this period was mainly on development of F1hybrids with multiple resistance to downy mildew (Pseudoperonospora cubensis Rostow), Phytophthora rot (Phytophthora melonis Katsura), anthracnose (Colletotrichum orbiculare (Pass.) Ell. & Halst.), and powdery mildew (Sphaerotheca fuliginea Pollacci) (6, 7). A number of desirable inbred lines, gynoecious lines, early F1 hybrids and multiple resistant F1 hybrids were developed. F1 hybrids became popular, and presently occupy 40% of the production area.
Achievements. Many favorable local cucumber cultivars (Cunjingzi, Erzhaozi, Tanshan Qiougua, Beijing Daci, Hanzhou Qinpi, Jin Zaosheng, Dabacha, Xiaobacha, Wenshang, Yeershan, Heihantui, Hanzhong Qiougua, Ninyang Cigua and Yangxian) were found and collected during the 1950s and early 1960s in different cucumber production areas with long growing histories. These local cultivars were used directly in commercial production, and also as breeding materials. These have been approximately 40 inbred and F1 hybrid cultivars developed since the late 1960s. The most popular inbred cultivars are Ningqin, JingYan No. 2, JingYan No. 4, JingYan No. 6, JingYan No. 7, Xingong No. 58, Xiafeng No. 1, Shanghai Cucumber, and Yiyu No. 2. The F1
hybrids grown extensively are Jingza No. 2, Zaofeng, Nongcheng No. 3, Zhongnong No. 5, 828, Xiaqing No. 1, Ningfeng No. 3, Xianhuan 881, Zhenhuan No. 2, Luhuan No. 1, and Bichong.
Screening systems of cucumber resistance to Fusarium wilt, downy mildew, Phytophthora rot, anthracnose, powdery mildew have been established in several research institutes and universities or colleges. Some screening programs were improved on the basis of those developed in foreign countries. Differentiation of downy mildew and Fusarium wilt fungus were extensively studied. The results obtained suggest that there is no race differentiation among downy mildew fungus isolates collected in different parts of China. All isolates of Fusarium wilt fungus collected in China show the same race reaction. The race of Fusarium wilt fungus in China is different from any of the races (1, 2, and 3) identified by Armstrong(1978). Race 4 was suggested for the Fusarium wilt fungus attacking cucumbers in China. Genetic study on cucumber is limited in China. Studies on quantitative inheritance and heterosis in cucumber carried out at Northwestern Agricultural University in recent years will make cultivar development more efficient (2, 5)
Future breeding objectives. The general objectives issued by the National Cucumber Research Association are to develop improved inbred and hybrid cultivars with resistance to multiple diseases for growing in different seasons and cultivation systems. There are as many as 15 diseases attacking cucumber in China. However, it is suggested that breeding work be focused on the most destructive diseases: downy mildews, Fusarium wilt, Phytophthora rot, anthracnose, powdery mildew and angular leaf spot (Pseudomonas lachrymans). The former three diseases led to the most serious problems for cucumber production in China. In addition, a more recently introduced disease from overseas, scab (Cladosporium cucumerinum Ellis & Arth.) is increasing in severity in Northeast China. It is expected this disease will be one of the most serious diseases unless great attention is paid right now. Early maturing inbred and hybrid cultivars will be preferred by cucumber growers because of their higher value in the spring production season. Much emphasis is placed on early maturity. Cultivars have been developed with high resistance to downy mildew and powdery mildew, and with tolerance to heat for fall production, but high-yielding cultivars with resistance to multiple diseases need to be developed.
The characters that Chinese breeders are interested in and in evaluating are resistance to downy mildew, Fusarium wilt, Phytophthora rot, anthracnose, powdery mildew and angular leaf spot, earliness and complex traits making cucumber favorable to fall production. Characters preferred by Chinese consumers include length/diameter >8, dark-green skin, and thick prominent spines.
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