Introduction and Use of Exotic Germplasm in the Chinese Sweetpotato Breeding Program

D.F. Ma1, H.M. Li1, and I.G. Mok2

Sweetpotato (Ipomoea batatas) was intro- low yield and poor adaptability when duced to over 400 years ago. Its high planted away from their place of origin. yield, wide adaptability, tolerance of abiotic That has been a serious constraint to the stresses, and versatility have contributed to expansion of sweetpotato production. In its traditional and continuing importance in 1938, Nancy Hall was introduced from the Chinese agriculture. Sweetpotato ranks USA. Preliminary evaluations were con- fourth among crops in planted area, about ducted in and . In 1941, 5.6 million ha, with mean yields higher the Japanese cultivar Okinawa 100 was than those almost anywhere else in the introduced and soon became the most world. In the 1950s and 1960s, the crop widely grown in northern China. Nancy was used mostly for food and feed, with Hall and Okinawa 100 became important only 10% of total production going to in both production and in breeding. starch extraction and food processing. In the 1990s, that has risen to about 45% of Modern breeding programs total production. Given the changes in use Modern sweetpotato breeding began in pattern, it is clear that high dry matter (DM) the late 1940s and early 1950s when the or high starch content is becoming more population explosion and severe food important. Most Chinese cultivars have low shortages led the government to emphasize or moderate DM content of <30% (XSPRC, sweetpotato production. Major efforts were 1993). Over the last 20 years, many devoted to sweetpotato breeding in prov- provincial breeding programs worked to inces with large sweetpotato planting areas. increase DM content and yield with little A number of new cultivars were developed success. Given the lack of progress, there using Okinawa 100, Nancy Hall, and some appears to be a need for an infusion of new local cultivars as parents. Most of the new sources of genetic diversity. cultivars had medium to low DM content. Xushu 18 is the cultivar most widely grown, Chinese Sweetpotato Breeding: with a planted area of 1.5 million ha. Its Past and Present DM content is about 25% (summer crop- ping in sandy loam soil in ) and Over the past 400 years, a number of local extractable starch content is 11-15% cultivars emerged due to selection pressure (XSPRC, 1993). Various institutes released by farmers and environmental changes. many cultivars. One of most successful after Forty-eight were listed in the Catalog of Xushu 18 was Nanshu 88, which was Sweetpotato Cultivars in China (XSPRC, released in 1988 by the Agricul- 1993), which contained 184 important tural Research Institute. It is, however, cultivars. Those cultivars possess tolerance grown only in Sichuan Province. of biotic stress and resistance to abiotic stresses. They are still grown in small areas To increase production and efficiency, in South China. However, most of them had key breeding units in China were organized into a national collaborative sweetpotato breeding project. Greatly improved col- 1 Xuzhou Sweetpotato Research Center, Xuzhou, China. laboration among provincial- and city-level 2 CIP, Bogor, Indonesia.

CIP Program Report 1997-98 311 research units resulted. Conventional have been released from crosses with hybridization is still the principal approach Okinawa 100 as a parent, and 33 from for sweetpotato breeding. Since the late Nancy Hall. Thirty-one cultivars were 1970s, Academy of Agricultural developed from cross combinations Sciences (AAS) and AAS paid between the two, including important more attention to collection, evaluation, cultivars such as Lizixiang, Yiwohong, and use of wild-relative species. Some Fengshouhuang, and Huabei 52-45. Nancy newly developed cultivars, such as Sushu 2 Hall and Okinawa 100 were dominant and Pushu 83-91, were bred with the among parents in breeding programs in introgression of genes from wild relatives. and Nanjing. In Beijing, Huabei New cultivars, Yi 306, Lushu 7, and Yushu 117, Huabei 166, Beijing 553, Beijing 284, 7, were selected from crosses with the Beijing 169, and others were selected from Japanese cultivar Minamiyutaka, which has crosses of these two parents. More than 70 12.5% of wild species genes in its pedigree. cultivars were selected from the crosses of Mutation breeding with 60Co radiation used Nancy Hall and Okinawa 100 after provin- to induce somaclonal variation has been cial breeding units were established in the used to improve sweetpotato. This work early 1950s. Some of them, such as was done at Beijing Agricultural University. Yiwohong, Beijing 553, and Lizixiang are As a result, Nongda 601, highly resistant to still planted in some places. black rot caused by Ceratosystis fimbriata, was selected from Xushu 18; and, Nongda In turn, Xushu 18, which has 75% of its 321-10, with resistance to stem nematode genes from Nancy Hall and Okinawa 100, (or brown ring caused by Ditylenchus has been widely used as parental material. destructor), was selected from Ning 12-17. Institute of Agricultural Sciences Although the use of Nancy Hall and selected a number of cultivars using fast Okinawa 100 led to the development of neutron radiation. These selected cultivars many successful cultivars, the genetic are high yielding and have high vitamin C background of sweetpotato has become content. The Xuzhou Sweetpotato Research narrow and limited. From 1986 to 1990, 21 Center (XSPRC) selfed elite clones, and of 23 cultivars released in China carried a selected two superior clones, Xuzi 39 and substantial number of genes from Nancy Pengwei S -12-48. None of these efforts, Hall and Okinawa 100. Nanshu 88 and Ji 1 however, resulted in a cultivar superior to 18-1 were the only two exceptions. Of 21 Xushu 18. new cultivars registered from 1990 to 1995, only Sushu 4 and Sushu 6 were not geneti- In recent years, postharvest processing of cally related to these two parents. sweetpotato has become an important way for farmers to increase their income. That The General Seed Company of China requires a high-yielding sweetpotato high in (1989) listed 42 cultivars grown on more DM content. Existing cultivars do not meet than 667 ha. Of these, 26 were considered these demands. Disease-resistant cultivars closely related to Nancy Hall or Okinawa with high starch content and high DM yield 100 or both, in that they have more than are urgently needed. 12.5% of their genes in common.

Inbreeding tendency in sweetpotato Sweetpotato breeding programs all over breeding China have extensively used Nancy Hall, Nancy Hall and Okinawa 100 have been Okinawa 100, Xushu 18, and other closely widely used as parental material since the related cultivars as parents. This practice beginning of the modern breeding program. caused severe inbreeding during selection, According to (1990), who analyzed the and limited the release of new, promising pedigree of cultivars listed in the Catalog of cultivars, especially those with high DM Sweetpotato Cultivars (1981), 41 cultivars content. Although more than 30 new

312 Sweetpotato cultivars have been released since 1990, shuttle breeding project with Japan (Table none can replace Xushu 18. These new 1). Seven advanced clones were introduced cultivars have low to medium DM content from CIP-Bogor. They had been selected at compared with many Japanese cultivars. three sites in Indonesia: Bogor (humid tropics, poor soil, 200 m), Lembang In recent years, more and more exotic (highland, cooler climate, 1600 m) and germplasm has been introduced through Malang (highly fertile soil, 700 m). These international cooperation. The breeding clones were initially selected based on strategy of CIP (Mok et al., 1998) strongly yield, DM content, starch content, and influenced sweetpotato breeding in China. adaptability to poor soils. Two clones Breeders paid more attention to broadening (190070-1 and 194039-1) selected at the genetic base by introducing exotic Xuzhou from CIP-Lima seeds were in- germplasm. With the introduction of cluded. Xushu 18 was used as a check. superior germplasm from CIP and Japan, the inbreeding tendency can be reversed to Seedling evaluation was done at Xuzhou achieve higher yields and DM content. by planting during the first week of June. Breeding materials from various sources, Advanced clones were multiplied at XSPRC including those from South America and and evaluated at , , and Africa, are expected to further broaden the Xuzhou. Clones were planted in random genetic base to incorporate resistance to complete block design with three replica- viruses and other diseases. The challenge is tions. The size of a single plot was 9.4 m2. to introgress these new genetic resources Cultivation was done according to the into highly-adapted, high-yielding Chinese standard method of each provincial AAS. commercial cultivars. Obviously, cultivar Harvest was 120 d after planting. DM introduction alone will not achieve these content of storage root was measured using goals. There is a need for further breeding. 200 g of longitudinally sliced strips. Drying oven temperature was set at 70oC until the Material and Methods samples reached constant weight.

Various sources of seed families have been Results and Discussion evaluated in China. Seed families from CIP- Lima had high DM content with resistance Botanical seed families from CIP have been to root-knot nematode (Meloidogyne spp.). introduced into China since 1990; more CIP-Nairobi sent seed families of high DM than 34,000 seeds have been evaluated. content with sweetpotato virus disease The number of families and their origin are resistance. Those from CIP-Bogor had high listed in Table 1. Seeds introduced in the DM content with wide adaptability. Seeds early 1990s had poor germination and low were also received from the cooperative adaptability, resulting in a low selection

Table 1. Evaluation of botanical seeds introduced to XSPRC from CIP.

Year Crosses Seeds received Seedlings planted Clones selected Origin 1992 33 1,700 600 12 CIP-Lima 1994 100 8,100 3,571 34 CIP-Lima, CIP-Bogor 1995 80 6,700 4,000 70 CIP-Lima, CIP-Bogor, CIP-Nairobi 1996 30 2,650 1,010 22 CIP-Lima, CIP-Bogor 1997 14 1,483 920 30 Shuttle-breeding families 1998 160 12,000 8,600 400 CIP-Lima, CIP-Bogor 1999 148 20,520 CIP-Lima, CIP-Bogor

CIP Program Report 1997-98 313 ratio. Selected high-yielding clones such as the nursery were discarded, 8,600 seedlings 490074-2 (from CIP-Lima, 1992) and were transplanted to the field. Finally, 400 B0080-1 (from CIP-Bogor, 1994) had low good clones were selected from the first DM content. These clones have already year seedling evaluation. Selection was been discarded from the CIP breeding based on good root shape and high DM program. content.

In 1995, large quantities of seeds were In 1998, seven clones were introduced introduced, most of them from crosses of from CIP-Bogor. Of these, enough planting high DM-content parents. Two clones from material was produced to test three clones CIP-Lima were selected, 194038-3 and (Group I) in Xuzhou, Jinan, and Chengdu. 194039-1. Both had high DM content, 35% Four clones (Group II) that did not produce for 194038-3 and 32% for 194039. They enough cuttings were tested only in had higher dry matter content than that of Xuzhou. The result of the evaluation of Xushu 18 (25-26%). After initial selection at Group I is presented in Table 2, and that of XSPRC, the 2 clones were sent to more than Group II in Table 3. The results indicated 10 breeding units around the country for that AB94001.8 (code name CIP-2) had further evaluation. Although the clones high DM content and high yield. Fresh were not released as cultivars, they were storage root yield of CIP-2 was almost the used as parental material in many prov- same as Xushu 18 (Table 2), but DM inces. In 1996, 22 good clones were content was higher than Xushu 18 at all selected from CIP seed families. Of these, three sites. This clone will be tested in Kawa 090-1 had 30% DM content, 4% demonstration trials in 1999. higher than Xushu 18. Further evaluation was done in 1998 with about 12,000 seeds, Clone AB94001.8 was initially selected 9,600 of which came from CIP-Lima, 2,200 in Indonesia from seed families obtained from CIP-Bogor, and 524 from the National through shuttle breeding. In evaluations of Agriculture Research Center (NARC), Japan. various introductions from many countries, The Japanese seeds were produced as a seed families from Japan were observed to part of CIP-NARC’s shuttle-breeding produce progenies having very high DM activity. With the adoption of improved content. The parental clones of these seed germination methods, about 90% of families also had high DM content in Japan seeds germinated. After inferior plants in (Tarumoto, 1989; Yamakawa, 1995).

Table 2. Multilocation trial of introduced high DM-content clones (Group I), China, 1998.

Clone Xuzhou Chengdu Jinan Mean DM FY DY DM FY DY DM FY DY DM FY DY (%) (t/ha) (t/ha) (%) (t/ha) (t/ha) (%) (t/ha) (t/ha) (%) (t/ha) (t/ha) AB94001.8 30.2 19.5aba 5.9a 32.3 28.4a 9.2a 39.4 11.2a 4.1ab34.0 19.7 6.4 AB95002.3 30.4 8.5c 2.6 b27.8 13.2 c 3.7 c 41.6 3.9 cb1.6 33.3 8.5 2.6 AB97001.1 28.2 14.4abc 4.1ab 28.3 13.2 c 3.7 c 38.5 6.2 b 2.4 bc 31.6 11.3 3.4 190070-1 31.8 12.1bc 3.8ab 33.3 13.5 c 4.5 bc 43.6 5.1 b 2.2 c 36.2 10.2 3.5 194039-1 30.2 21.2ab6.4a 32.3 17.1 b5.5 b40.6 8.2ab3.3abc34.4 15.5 5.1 Xushu 18 24.4 24.2a 5.9a 30.3 30.7a 9.3a 35.1 12.4a 4.3a 29.9 22.4 6.5 DM = dry matter content, FY = fresh storage root yield, DY = dry matter yield. a. Mean separation within columns by Duncan’s multiple range test at P = 0.05.

314 Sweetpotato Table 3. Single-location trial of introduced high DM-content clones (Group II), Xuzhou, China, 1998.

Clone DM (%) FY (t/ha) DY (t/ha) AB94002.7 29.7 4.9 1.46 AB95002.7 32.8 10.8 3.54 AB94078.1 33.7 13.8 4.65 AB95012.4 25.0 8.4 2.10 Xushu 18 24.0 20.6 4.94 DM = dry matter content, FY = fresh storage root yield, DY = dry matter yield.

Obtaining botanical seeds in quantity Indonesia, seemed to perform satisfactorily from Japan was difficult due to the cost of at the evaluation sites in China. Clones seed production. Moreover, all of the selected in Indonesia for high DM content recently-released cultivars, which are almost always tested high for DM content frequently used for hybridization, are in China. The heritability of DM content protected under the breeders’ rights law in was 61.2% (Mok et al., 1997b). It is likely Japan. To overcome these limitations, that this trait could have a small genotype shuttle breeding was suggested (Takagi, H., by environment interaction. Japanese International Research Center for Agricultural Science and Komaki, K., Conclusion National Agricultural Research Center, pers. comm.). CIP sent a trainee to NARC to learn In China, popular sweetpotato cultivars hybridization techniques using high DM- mostly have low to medium DM content. content cultivars such as Minamiyutaka, Two major reasons for this are the narrow Satsumahikari, and Hi-starch. Ipomoea nil, genetic base and the high yield focus of a dwarf morning glory, which had strong breeding programs. Recent developments in flowering induction ability, was used as starch processing from sweetpotato in grafting stock. Three trainees from develop- China require cultivars with high DM ing countries were sent to Japan, one each content and high starch content. Collabora- in 1996, 1997, and 1998. Hybrid seeds tive research with CIP makes the exchange produced were evaluated in China, Indone- of genetic resources possible with unprec- sia, and Vietnam. DM content in the edented speed. As a result, a number of breeding population was rapidly increased high DM clones have been selected and using these seed families. introduced. These materials are under evaluation in many provinces where Another clone, AB94078.1, was selected sweetpotato is important. These preliminary at CIP-Bogor from seed families of CIP- results indicate it is possible to select Lima. This clone had the highest DM cultivars for high DM content, high yield, content of all clones tested at Xuzhou and wide adaptability in China. This effort (Tables 2 and 3), and also gave the highest will have a major impact in many provinces DM content (39%) at three distinctively where starch processing is a major source different environments in Indonesia (Mok et of farmers’ income. al., 1997a). This clone has already been distributed to other breeding units in China. References Cited

Two main selection criteria at CIP-Bogor General Seed Company of China (GSCA). were high DM content and wide adaptabil- 1989. Statistical table on major crops in ity (Mok et al., 1997b). These AB series China. GSCA, Bejing, China. 93 p. clones, selected for wide adaptability in

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