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This map displays primary areas of potato cultivation and yields, reported by province in China, based on data provided by Chinese National Government statistics for the year 2003 (national total almost identical to data reported by the United Nations Food and Agriculture Organization, FAO).

Yield data are presented as average values for each province, although there is of course likely to be considerable variation within each (most much larger in population than several countries). This averaging effect might account for apparently odd disparities between areas of very high reported yields adjacent to areas of much lower yields.

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Abstract

Late blight has become the main devastating disease threatening potato production world wide since its outbreak resulting in its notorious Irish potato famine in 1840’s and its outbreak in early 1950's in China countrywide. Priorities of the disease management have been primarily given to selection and use of resistant varieties, as well as application of fungicides including systemic Ridomil (metalaxyl) or contact Dithane M-45. However, because of quick losses of host resistance to the pathogen due to either presence or absent of the major genes in the host or development of pathogen resistance to fungicides, it is practically more difficult to manage the disease. Socioeconomic factors and environmental considerations also add to the issue in developing countries.

The paper reviews some practical and basic work on epidemiology, race identification, chemical control and preliminary genetic engineering on the resistance that has been carried out in China. In collaboration with the International Potato Center (CIP), further research on evaluation and large scale of extension of the resistant clones/varieties, pathology of the races and mating types (A1/A2), and genotype by environment (GxE) interactions on the expression of late blight horizontal resistance and variation has been and is being conducted. Future prospects depend largely on plant breeding to resistant varieties and integrated pest management (IPM).

Introduction

Late blight is a major limitation to potato production. Epidemics occur more frequently in the southern part and particularly in the southeast of China because of heavy rainfall and the long rainy season. Most seed potato production takes place in the north and when epidemics occur there a high proportion of the seed can become infected and be distributed throughout the country. The main source of primary infection is diseased seed tubers. Both tomato and potato are hosts of Phytophthora infestans.

Late blight occurrence and LB severity by major production area in the country

LB impact

According to an incomplete survey in 1996, yield loses ranged from 5 to 60% and economic loses were estimated to be USA $170 million. This does not account for tubers rotting in storage.

Fungicide use

• Ridomil 25 WP with 500×
• Ridomil MZ 58 WP with 500~600×
• Bordeaux mix 100×
• Ditane M-45 WP with 800×
• Daconil 75 WP with 600~800×
• Fosetyl-A1 MZ 70 WP with 300×
• Curzate M-8 72 WP with 600~800×
• Flumorph MZ 60 WP with 500~1000×

Chemical control primarily used for seed production, research trials and fields of potatoes grown for processing. Spraying is usually 7–10days. In northern China 2–3 sprays usually gives good control.

Other LB control measures

Host resistance. Through the CIP-China project, a large amount of germplasm has been introduced from CIP and evaluated for late blight resistance among the other resistances and traits. A number of promising clones and varieties, especially of CFK69.1, I-1085 and S88, have been identified or selected from CIP germplasm or from CIP introduced TPS with high late blight resistance as well as other good agronomic characteristics have been identified, especially in Southwest China. Some of them have entered official multi-regional trials and put into seed production program to accelerate the multiplication for farmers' use. Others have been used as parental lines to breed late blight resistance. (Wang et al., 1990; Hu et al., 1994).

Transgenics. Transgenic potato plants expressing late blight resistance through introduction of HarpinEa and Osmotin genes have been obtained (Li et al., 1997). Years of work on creating clones regenerated from fused protoplastes by somatic hybrid method between dihaploid of Solanum tuberosum and diploid S. phureja or S. chacoense were carried out (Dai et al., 1994; Si Huaijun & Dai Chaoxi, 1997).

Forecasting. An effective late blight warning system (PLB-1) has been developed (Cao et al., 1998). It is based on PhytoPRE+2000, which was developed in Switzerland. The warning system and forecast model established in Belgium was extended in Chongqing city since 2000 and performed well (Zhang et al., 2004). An model was also develeped recently in Yunnan province (personal communication with Yang Yanli, 2004).

Cultivation practices. Cultivation practices can change the microclimate in the fields and prevent pathogen spread. The method cannot eradicate late blight, but it can reduce both the disease and yield loss. Moreover, because more and more potato starch manufacturers request potato production without pesticides, the popularization of cultural practices is imperative. Wide row planting, hilling up in time, fertilizing properly, cutting the stems and leaves above the ground 10-15 days ahead of harvest are some ways to lighten disease. Further studies are needed.

LB control effectiveness

Late blight resistant cultivars. Cultivars with major gene resistance were introduced and released in late 1960’s and early 1970’s. They started to become susceptible to late blight in the 1980’s.

Pathogen strains

Mating type. Both A1 + A2 are present. A2 was first detected in the north of China in 1996. Three of 134 isolates tested in the Yunnan province during the winter 2000-2001 were A2.

Fungicide resistance. About 15% of the 134 P. infestans isolates collected during 1996 to 1998 from the potato growing provinces of Inner Mongolia, Hebei, Zhongqing, Shichuang and Yunnan and tested for metalaxyl resistance were intermediately resistant — none were resistant. The isolates from the provinces of Inner Mongolia, Hebei and Zhongqing had the highest frequency (20.0 – 28.6%), most likely due to earlier use of metalaxyl, while those from Sichuan and Yunnan had the lowest (0 – 4.8%) frequency. Isolates from the potato production areas in the northeast and northwest have not yet been tested. Isolates obtained from naturally infected potatoes en Yunnan from November 2000 to January 2001 were 71.1% sensitive, 16.9% intermediate and 12% resistant of a total of 83 tested.

Virulence factors/physiological races. To determine physiological races of isolates from Yunnan collected 2000–2001, plant differentials for R1, R 2, R3 and R4 were used in addition to Atlantic, which has no know R genes. Seventy-seven isolates were tested and four races were detected: Race 0, Race 3, Race 4 and Race 3,4 with frequencies of 32.5, 15.6, 39 and 48%, respectively. Isolates from tomato fields were Race 0. Race 0, 1, 3, and 3.4 are the ones occurring in Yunnan in which Race 3 is the dominant taking over 30%.

Aggressiveness. Isolate from each of the five races were inoculated on 8 potato varieties. The most aggressive isolate was Race 0 (A2), followed by Race 3,4, (A1) Race 3 (A1), Race O (A1) and Race 4 (A1).

Disease risks and/or major needs

Because of rapid losses of host resistance to the pathogen due to either presence or absence of the major genes in the host or development of pathogen resistance to fungicides, managing the disease is much more difficult. In addition, social economic factors and environmental considerations add up to the issue, as most framers can not afford chemical control.

Highlights of the national research work on late blight in China

From 1952 onward, the late Prof. Lin Chuanguang et al initiated research work on late blight epidemiology including occurrence of the core diseased plant due to the seed infection, spread of the disease, hence prediction and control of the disease based on climatic conditions (Zhang & Song, 1993). Their results and integrated measures were disseminated to farmers with success (Zhang & Song, 1993).

The work of identification, distribution and variation of the races of the pathogen Phytophthora infestans was consequently carried out in the North by Lin, Huang, Zhang, Li, etc. from 1960's to 1980's, which provided necessary information for breeding resistant varieties due to the major races identified (Zhang & Song, 1993).

At the meantime, because of the losses of host resistance to the pathogen, priority was given to chemical application to control the disease. Several fungicide chemicals were identified to be effective, to name a few in the descending order: metalaxyl (Ridomil) especially when contained with addition of Mn and Zn, Bordeaux mixture, copper sulfate mixture, lime, etc. Those conclusions confirmed many of the other similar results elsewhere.

Some laboratory work has been done over the last years. Transgenic potato plants expressing late blight resistance through introduction of HarpinEa and Osmotin genes have been obtained (Li et al., 1997). Years of work on creating clones regenerated from fused protoplasts by somatic hybrid method between dihaploid of Solanum tuberosum and diploid S. phureja or S. chacoense were carried out (Dai et al., 1994; Si Huaijun & Dai Chaoxi, 1997); Systematic research and thorough review on the pathogen biology and techniques have been done (cf. Li, 1988; 1984). Besides, an effective late blight warning system (PhytoPre) has been developed (Cao et al., 1998).

Location of dominant alleles of R gene, mapping of quantitative trait loci for field resistance, molecular mechanism between host and P .infestans, defense-related gene cloning and genetic improvement were remarkably worked out recently (Tian et al., 2004).

The recently interesting findings by Cao et al. (2001 and this proceedings) showed the apparent inhibiting effectiveness of five plant extracts to the infection of P. infestans on detached potato leaves of Bintje.

Collaboration with CIP on late blight in China since 1986

Through the CIP-China project, a large amount of germplasm has been introduced from CIP and evaluated for late blight resistance among the other resistances and traits. A lot of promising clones and varieties especially of CFK69.1, I-1085 and S88 have been identified or selected from CIP germplasm or CIP introduced TPS with high late blight resistance as well as other good agronomic characteristics compared with the controls especially in Southwest China (Wang et al., 1990; Hu et al., 1994). Some of them have entered official multi-regional trials and put into seed production program to accelerate the multiplication for farmers' use. Some of them have been used as parental lines to breed late blight resistance (Wang et al., 1990; Hu et al., 1994).

There is a growing concern of the A2 mating type since its finding in western Europe in the mid-1980's, because when A1 and A2 exist in the same location they mate sexually, producing hard-hulled oospores that can survive in the soil for longer period (CIP, 1996a). The earliest report of the A2 as well as A1 in (northern) China was in 1996. Further research on races, distribution, frequency, mating efficiency, resistance to metalaxyl, and survivability of oospore of A2 is under way. GILB coordinated by CIP is undertaking an ambitious worldwide program on late blight, including breeding, pathogen studies, IDM, training and information exchange network. IFAD is also implementing a project on late blight IDM through participatory farmer’s school in China.

The experiments of a Line X Tester we conducted showed significant differences of late blight foliage damage and yield components over two contrasting environments (Sichuan and Yunnan) in humid Southwest China (Table 1). Several crosses were identified to be highly or intermediately resistant to the disease in comparison with the controls. The population was derived from R gene-free germplasm and crosses, hence the resistance is of horizon. Furthermore, the combined analysis of the two locations indicated that there were significant interactions of genotype and environment (GxE) both for late blight resistance and tuber yield. That would indicate the characteristics of multigenic effects expressed in host resistance.

Note: Yield is t/ha; AUDPC is degree of late blight resistance; * significant at 5% level, ** at 1% level ;  *** at 0.1% level.

Discussion and future prospects

As reviewed above for the national and international programs, there is an urgent need to bridge gaps between the pathological aspects and genetic hence breeding methods to develop durable host genetic (non-specific, multi-genic, horizontal or field) resistance rather than vertical (major-genic) resistance to the pathogen Phytophthora infestans (cf. Landeo, 1993; CIP, 1996b) and eventually put to practice. Development of R-gene free population would reduce the interference of R genes in breeding for high levels of horizontal resistance against P. infestans, and facilitate and simplify the breeding process, which has become the strategy of top priority at CIP to date (Landeo, 1993a; 1993b; 1993c).

The preliminary achievement on genetic engineering provides promising future for late blight resistance. However, a lot of work especially on linkage with conventional breeding and agronomy needs to be done. Closer cooperation project, communication and training may play a key role to realize such work.

Integrated pest management (IPM) is to be developed and put into practice based on available and new agronomic practices such as crop rotation, intercropping, properly early haulm killing prior to harvesting, use of resistant varieties, and so on. CIP via GILB (Global Initiative on Late Blight) has started to play a leading role in combating late blight worldwide, and we expect the fruitful achievements with the comprehensive research and extension work in the large-scale cooperation network.

There is an urgent need to bridge gaps between the pathological aspects and genetic hence breeding methods to develop durable host genetic (non-specific, multi-genic, horizontal or field) resistance rather than vertical (major-genic) resistance to the pathogen P. infestans. Development of R-gene free population would reduce the interference of R genes in breeding for high levels of horizontal resistance against P. infestans, and facilitate and simplify the breeding process. Tuber blight is also a severe problem particularity in Southwest China.

Literature cited

Cao Keqiang and Hu Tongle. 2001. PLB-1 A warning system on potato late blight in China. pp 38–47 in: Proceedings of the International Workshop on Potato Late Blight, 15–19 October 2001, Pyongchang, Ganwon, Korea. National Alpine Agricultural Experiment Station, RDA, Pyongchang, Korea. 

Cao, K.Q. and H.R. Forrer. 2001. Current status and prosperity on biological control of potato late blight (Phytophthora infestans). Proceedings of the GILB East and Southest Asia Linkage Group International Workshop on Late Blight, 16–20 August, Baoding, Hebei, China. Journal of Agricultural University of Hebei 24(2): 51-58.

Dai et al. 1994. Research on potao cell diffusion by electroform. Journal of Lanzhou University 30: 82–87.

Forrer, H.R., H.U. Gujer and P.M. Fried. 1993. PhytoPRE - A comprehensive information and decision support system for late blight in potatoes, from the Workshop on Computer-based Decision Support System (DSS) in Crop Protection, Parma, Italy, November 23-26 1993.

He Wei and Paul C. Struik. 1998. Analysis of the potato disease and pest status in Southwest China. Chinese Potato Journal 3: 131–135.

Hu (et al.) Qunbao, Wang Jun, Song Bofu and Enrique Chujoy. 1994. Evaluation of CIP's introduced germplasm for resistance to Phytophthora infestans in Yunnan, China. In: Proceedings of the 4th Asian Potato Association Conference, Korea.

Li (et al.) R.G., Wu N.F., Fan Y.L. and Song B.F. 1997. Review of research and progress on potato late blight resistance. Chinese Potato Journal 44: 243–250.

Si Huaijun and Dai Chaoxi. 1997. Morphology and agronomic traits of potato plant derived from inter-species somatic hybridization. Chinese Potato Journal 44: 193–196.

Ryu K.Y, W.F. Lou and Y. Wang. 2001. Status of potato late blight (Phytophthora infestans ) in Yunnan Province of Southwest China.pp 106–120 in: Proceedings of the International Workshop on Potato Late Blight, 15–19 October 2001, Pyongchang, Ganwon, Korea. National Alpine Agricultural Experiment Station, RDA, Pyongchang, Korea.

Tian Zhengdong, Xie Conghua, Liu Jun and Hu Cheng. 2004. Advance in molecular mechanism of potato resistance to Phytophthora infestans. pp.209–211 in: Proceedings of the Fifth World Potato Congress, Kunming, China.

Wang, Jun, Hu Qunbao, He Tingfei, Jiang Facang and Song Bofu, 1990. Late blight evaluation and yield adaptation of CIP's potato germplasm in Yunnan. In: CIP-China potato and sweetpotato projects progress. China Agric. Sci. & Tech. Press.

Xie Kaiyun and Wang Yi. 2001. CIP potato late blight research in China. Journal of Agricultural University of Hebei 24 (2): 44–48.

Zhiming Zhang, Befu Song and Zhihui Yang. 2001. Integrated control on potato late blight. pp 1–9 in: Proceedings of the International Workshop on Potato Late Blight, 15–19 October 2001, Pyongchang, Ganwon, Korea. National Alpine Agricultural Experiment Station, RDA, Pyongchang, Korea.

Zhiming Zhang, Yuqin Li, Jiehua Zhu and Shimin Tian. 2001. Preliminary study on metalaxyl-resistant isolates of Phytophthora infestans in China. pp 101–105 in: Proceedings of the International Workshop on Potato Late Blight, 15–19 October 2001, Pyongchang, Ganwon, Korea. National Alpine Agricultural Experiment Station, RDA, Pyongchang, Korea.

Zhang Zhiming and Wang Rengui. 2001. Progress and suggestion on potato late blight research in China. Proceedings of the GILB East and Southest Asia Linkage Group International Workshop on Late Blight, 16–20 August, Baoding, Hebei, China. Journal of Agricultural University of Hebei 24 (2): 4–10.

Zhang Zhiming, Zhu Jiehua, Song Bofu, Li Yuqin, Tian Shimin and Jiang Hushan. 2001. Further investigation on A2 mating type of Phytophthora infestans in China. Proceedings of the GILB East and Southest Asia Linkage Group International Workshop on Late Blight, 16–20 August, Baoding, Hebei, China. Journal of Agricultural University of Hebei 24 (2): 32–37.

Zhang Zhiming, Cao Keqiang, Gui Xiumei and Yang Zhihui. 2004. Advance on epidemic and forcast of potato late blight in China. pp.187-189 in: Proceedings of the Fifth World Potato Congress, Kunming, China.

[1] Proceedings of the Regional Workshop on Potato Late Blight for East and Southeast Asia and the Pacific held 24–25 August 2004 in Yezin, Myamar. Posted on GILB website and in press.

[2] Sichuan Academy of Agricultural Sciences, Chengdu, China, email: hew(at)mail.sc.cinfo.net  

[3] Hebei Agricultural University, Baoding, China

[4] Chinese Academy of Agricultural Sciences, Beijing, China

Links to World Potato Atlas (WPA)

http://research.cip.cgiar.org/confluence/display/wpa/China