EFFECTS OF SULFUR ON KIWIFRUIT CANKER CAUSED BY PSEUDOMONAS SYRINGAE PV

The inhibition effect of sulfur on kiwifruit canker, caused by Pseudomonas syringe pv. actinidiae (Psa), by using turbidimetry and the inhibition zone method was investigated. It determined the control effects of sulfur on kiwifruit canker in pot and field experiments, as well as the effect of sulfur on defense enzyme activities in kiwifruit leaves. The results showed that sulfur had an inhibition role during the logarithmic phase of Psa growth and could inhibit the division and proliferation of the pathogen. However, toxicity was weak and its EC50 value was 1326.99 mg/l. When Psa was inoculated onto potted kiwifruit vines, the incidence rate was lowest on kiwifruit vines with the 1.5 kg/m sulfur treatment. The control effect was up to 73.34% better than those that had not been treated with sulfur. The incidence rate was lowest when the kiwifruit plants were treated with 2.0 kg/m sulfur. Furthermore, the control effect was up to 76.67% at two years after sulfur treatment. Sulfur could improve superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and phenylalanine ammonia lyase (PAL) activities in kiwifruit leaves when they were treated with 0.5 3.0 kg/m sulfur, and kiwifruit plant disease resistance was enhanced to some extent. The pot experiment indicated that SOD, CAT, POD, and PAL activities, and disease resistance in kiwifruit leaves were highest when the plants were treated with 1.5 kg/m sulfur. However, the field experiment showed that SOD, CAT, POD, and PAL activities, and disease resistance in kiwifruit leaves were highest when the leaves were treated with 2.0 kg/m sulfur. These results demonstrated that moderate applications of sulfur and organic fertilizer can significantly improve defense enzyme activity in kiwifruit leaves and increase plant resistance to disease. Introduction Kiwifruit (Actinidia deliciosa) has a unique flavor and is the most nutrient dense of all fruits (Cassano et al. 2004). It is often called ‘the king of fruits’ due to its good reputation. In recent years, damage caused by kiwifruit canker at planting time has become more serious year after year which has posed a threat to the production of the fruit (Prencipe et al. 2016). Kiwifruit canker is caused by Pseudomonas syringae pv. actinidiae (Psa) and has become one of the most destructive kiwifruit orchard diseases in the United States (Rees-George et al. 2010, Zhao et al. 2015), Japan (Takikawa et al. 1989), New Zealand (Everett et al. 2011), South Korea (Koh et al. 2010), Greece (Holeva et al. 2015), and other countries (Balestra et al. 2009). The first case of kiwifruit canker disease in China was reported at Dongshanfeng farm, Hunan Province. Since then, kiwifruit canker has occurred in many places in China, including Shanxi, Sichuan, Hunan and Guizhou, and has been listed as a national forest plant quarantine disease (Gao et al. 2012). Over the past several years, kiwifruit canker has occurred so frequently and seriously that considerable amounts of chemical pesticide have been applied, which has led to pathogen resistance against the bactericides (Frampton et al. 2014). Therefore, alternative management strategies to effectively control kiwifruit canker need to be investigated. *Author for correspondence: . Institute of Crop Protection, Guizhou University, Guiyang, Guizhou 550025, China.