Major progress in research on resistance to cotton Verticillium wilt

Verticillium dahliae is a devastating plant pathogenic fungus with an extremely wide host range, able to infect as many as more than 400 plant species, including many crops of important economic value. Worldwide, losses from Verticillium wilt caused by Verticillium dahliae exceed several billion US dollars every year. Cotton Verticillium wilt caused by Verticillium dahliae is the most serious fungal disease in cotton-growing regions worldwide, not only significantly reducing cotton yield but also greatly lowering fiber quality. In ordinary outbreaks it reduces yield by 10%-30%, and in severely affected cotton fields the yield reduction can reach more than 80%, or even a total crop failure.

In 1935, when Stoneville cotton was introduced from the United States, Verticillium dahliae was brought into China and then spread rapidly. At present, about half of the cotton-growing area in China is affected by Verticillium wilt, making it the most serious disease in cotton production, with economic losses of 1.5-2 billion yuan each year, an enormous loss.

Verticillium dahliae is a soil-borne pathogen that forms microsclerotia in the soil and survives adverse conditions for more than 10 years. To date there is no effective fungicide in production, so breeding disease-resistant cotton varieties is considered an important means of controlling Verticillium wilt. However, owing to the lack of effective resistance sources, no highly resistant variety has yet been successfully bred. Therefore, Verticillium wilt has long been regarded as the "cancer" of cotton.

Gastrodia elata is a traditional Chinese medicinal material and has a medicinal history of more than 1,000 years in China. Research has found that a small-molecular-weight Gastrodia antifungal protein present in the epidermis and cortical parenchyma cells of Gastrodia tubers is the basis of this defense system. In vitro antifungal activity tests show that gafps have very broad-spectrum antimicrobial activity and strongly inhibit many plant pathogenic fungi, indicating great application prospects in plant antifungal disease genetic engineering.

Wang Yiqin, an associate researcher at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, cloned a Gastrodia antifungal protein gene from Gastrodia elata by methods such as protein purification, sequencing and cDNA library screening, named it gafp, and proved that gafp has good resistance to a variety of fungi including Verticillium wilt. Further screening of the Gastrodia genomic library revealed that 4 gafp genes exist in Gastrodia. Through comparative studies of the activity of the 4 members, it was found that a new member, gafp4, has the strongest antimicrobial activity both in vivo and in vitro, and its signal peptide carrying intercellular localization can significantly enhance resistance. Through more than 10 years of cooperation with the research group of Li Fuguang, a researcher at the Cotton Research Institute of the Chinese Academy of Agricultural Sciences, the research group of Jian Guiliang at the Institute of Plant Protection of the Chinese Academy of Agricultural Sciences, and the research group of Jiao Gaili, a researcher at the Cotton Research Institute of the Shanxi Academy of Agricultural Sciences, gafp4 was transferred into 2 upland cotton cultivars, and continuous three-year Verticillium wilt identification trials in Verticillium wilt disease nurseries in three locations, Yuncheng in Shanxi, Anyang in Henan and Langfang in Hebei, showed that gafp4 has very obvious resistance to Verticillium dahliae strains of different physiological types and is an effective protein for high resistance to cotton Verticillium wilt. Most importantly, gafp4 transgenic cotton also showed a 20.7%-51.7% increase in fiber yield. Therefore, this research result provides the possibility of overcoming cotton's "incurable disease" through plant genetic engineering.