Picture of a wheat head infected with Fusarium scab

Recent Advances in Wheat Head Scab Research in China

Li-Feng Chen, Gui-Hua Bai, and Anne E. Desjardins

Introduction

USDA, Agricultural Research Service

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Introduction

Pathogen Biology

 Breeding

 Resistance

Mechanisms

Evaluation

Disease Control

Conclusions

References

Researchers

Other Resources

Glossary

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 Distribution of Wheat Head Scab in China

Green = Severe
Orange = Mild
Yellow = Sporadic
 
 
 
 
 
 
 
 
 
 
 

Robert Stack, Fusarium Head Blight of Small Grains,
APSnet Article

 

 

 

 

 

Hershman et al.,
Cooperative WHS Survey 1998-1999, 1999-2000

Wheat (Triticum aestivum) is the second most important food crop in China. Wheat cultivation occupies an estimated 30,000,000 hectares and is exceeded only by rice in cultivated area and grain production (Xu and Chen, 1993). Farmers in China grow spring wheat cultivars which are not winter hardy, and winter wheat cultivars which are able to survive the winter by vernalization. The first outbreak of WHS was reported in 1936 in regions along the middle and lower reaches of the Yangtze River in central China. In this outbreak, the percentage of scabbed spikes was as high as 95% in cultivar Jinda 2905 in Xuancheng County, Anhui Province (Xu and Chen, 1993). Since then, WHS has occurred frequently in winter wheat in central China, including the provinces of Jiangsu, Zhejiang, Anhui, Hubei, and the municipality of Shanghai. WHS has also occurred in spring wheat in northeast China, including Heilongjiang Province. During the last 15 years, an increasing number of wheat-growing regions throughout the country, including the provinces of Henan, Shaanxi, Ningxia, Gansu, Qinghai, Hebei, Shandong, and Sichuan have been affected by the disease (Li, 1989; Zhang, 1989; Yang and Li, 1995; Gan and Zhang et al., 1996; Liu, 1997; Yu, 1997; Lu and Tan et al., 1998; Zhang, 1998; Guo and Li et al., 1999). In 1985, an outbreak of WHS occurred in an area of approximately 3,300,000 hectares in Henan Province (Li, 1989). From 1987 to 1997 in Sichuan Province, there were five serious WHS epidemics in the years 1989, 1990, 1992, 1996, and 1997, aMap showing the distribution of wheat head scab in China frequency much higher than that in other areas (Li, 1996; Liu, 1997). In 1998, wheat growers in China suffered another severe epidemic of WHS. In the regions of the Huai River and the Yellow River, this epidemic is the most severe WHS outbreak in the historical record (Bai and Fan, 1998; Lu and Tan et al., 1998; Zhang, 1998; Guo and Li et al., 1999; Shi and Wang, 1999; Zhu, 1999). All available data indicate that WHS epidemics are becoming more frequent, more severe, and more widespread in China.

Economic Losses Due to Wheat Head Scab

WHS epidemics can cause great, direct yield losses. In severe epidemics, the percentage of scabbed spikes (disease incidence) is usually 30 to 50%, but can exceed 60 to 70% in the most susceptible cultivars in the most severe epidemics (Zhang, 1998; Bai and Fan, 1998; Lu and Tan, 1998; Shi and Wang, 1999). The epidemic of WHS in Henan Province in 1985 caused a yield loss of 890,000 metric tons (Li, 1989). The outbreak of WHS in Sichuan Province in 1996 resulted in a yield loss of about 78,000 metric tons (Li, 1996). Data on wheat yield losses for the whole country due to head scab epidemics are not yet available.

In addition to direct yield losses, WHS causes further indirect economic losses. The quality of WHS infected wheat kernels is reduced due to changes in protein content and to contamination with mycotoxins (Xu and Chen, 1993; Wu and Peng, et al., 1996; Wu and Wu et al., 1997). When used as seeds, the infected kernels germinate poorly, and the seedlings can easily become blighted, which indirectly reduces the yield (Xu and Chen, 1993; Bai and Shaner, 1994). F. graminearum, the major pathogen of WHS, produces two major classes of mycotoxins: trichothecenes and zearalenone. Trichothecenes are toxic to human beings and animals, and cause dizziness, headaches, nausea, vomiting, abdominal pain, diarrhea, fever, and sleepiness in human beings, and cause food refusal and diarrhea in animals (Xu and Chen, 1993). Zearalenone causes infertility and abortion in pregnant female animals, especially in pigs (Xu and Chen, 1993). In China, some human diseases, such as Kashin-Beck disease and esophageal cancer, have been epidemiologically associated with consumption of trichothecenes, but the correlation has not been well established (Chu and Li, 1994; Zhang and Guo et al., 1996; Yang, 1997).

Guidelines for Human Consumption of Scabbed Wheat

Although the role of mycotoxins in human diseases is unclear, some preventive measures have been taken by the Chinese government. To safeguard human health, a limitation of 5 to 6% scabbed grains in wheat was established in the early 1960s (Lu and Xue, 1995). Wheat with more than 6% scabbed grains was not allowed for human or animal consumption. This standard has subsequently been modified to 4% scabbed grains and accepted as an official standard by the Chinese government (Xu and Chen, 1993). A stricter standard with 3% scabbed grains has been proposed, but has not yet been approved by the government (Lu and Xue, 1995).
Two recent surveys of naturally contaminated wheat in China have shown that the levels of the trichothecene toxin, deoxynivalenol Chemical structure of DON(DON), are correlated with the percentage of scabbed kernels (Lu and Xue, 1995; Xie and Wang, 1999). Standards based on levels of DON, i.e., no more than 2,000 µgram of DON per kg of wheat, have been proposed (Luo, 1989; Xie and Wang, 1999), and are pending official approval by the Chinese government.

Brief History of Wheat Head Scab Research in China

In China, research on WHS began in the 1930s. First, Wu (1939) described the disease symptoms, pathogen morphology, life cycle, and host range, and the environmental conditions favorable for the disease. Then, Dai (1941) found remarkable differences in wheat resistance to head scab among 41 wheat cultivars. From the 1950s to the 1960s, research focused mainly on pathogen biology, factors affecting disease development, and chemical control. The establishment of the China Wheat Scab Cooperation Group (CWSCG) led to great progress in the 1970s and 1980s. CWSCG identified 18 Fusarium species causing WHS in China, and developed several techniques to test wheat resistance to head scab. CWSCG also identified Sumai 3, Ning 7840, Wangshuibai, and other good resources for WHS resistance breeding by screening more than 30,000 collections of wheat germplasm from China and other countries (Wang and Liu et al., 1989). In addition, CWSCG proposed an integrated control strategy for WHS that combined the use of resistant cultivars with application of fungicides to reduce the yield loss due to WHS. Fungicide mixtures and application strategies have been developed to slow the development of resistance in F. graminearum to carbendazim, a benzimidazole fungicide that has been widely used for WHS control in China (Shao and Liu et al., 1998). Recently, wheat breeders have been continuing their efforts to develop resistant cultivars by combining conventional breeding methods and new techniques, such as tissue culture, recurrent selection, and transfer of head scab resistant germplasm from alien species (Liu, 1994; Lu and Jiang et al., 1995; Jiang and Wu, 1996). Plant pathologists and wheat breeders have also initiated research on physiological and biochemical mechanisms of WHS resistance, which should provide basic information to aid WHS resistance breeding.

 

 

 

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