1.14.9
THE EFFECT OF PLANT-PARASITIC NEMATODES ON SEVERITY OF BACTERIAL WILT IN SOLANACEOUS PLANTS IN TAIWAN

CY LIN1, JH YEN1, DY CHEN1, SH HSEU1 and TT TSAY2

1Department of Plant Pathology, Taiwan Agricultural Research Institute, Wufeng, Taichung, Taiwan, ROC; 2Department of Plant Pathology, National Chung Hsing University, Taichung, Taiwan, ROC

Background and objectives
Ralstonia solanacearum (Smith) Yabuuchi is one of the most important pathogens in tropical and subtropical areas. It attacks more than 200 crops and causes extemal wilting symptoms under high relative humidity and temperature conditions [1]. The infection rate is over 90%. Bacterial wilt resistance breeding has been executed in Taiwan since 1972. The main control method is to use resistant varieties, but cultivation of a high-resistance variety is still continuing. The results of investigations show the existence of plant-parasitic nematodes in over 70% of bacterial wilt-infected areas, including root-knot nematodes, lesion nematodes, and reniform nematodes. In general, plant-parasitic nematodes can produce wounds in the root of a host plant to let in bacteria or fungi easily. Besides, nematodes also can destroy the resistance of a resistant plant [2]. The hypothesis for serious yield loss by bacterial wilt of plants in Taiwan is that plant-parasitic nematodes and bacteria may have complex interactions. The purpose of this research is to investigate the distribution and severity of the disease complex between bacterial wilt of plants and plant-parasitic nematodes in Taiwan, to search for the mechanism of complex infection between bacterial wilt and plant-parasitic nematodes, and to try to find a suitable control method.

Results and conclusions
The distribution of the disease complex between bacterial wilt of solanaceous plants and plant-parasitic nematodes in central Taiwan was investigated. The investigation showed the existence of plant-parasitic nematodes in nine locations of a bacterial wilt-infected area, including root-knot nematode (Meloidogyne incognita) and lesion nematode (Pratylenchus penetrans). Studies on the effects of plant-parasitic nematodes on the severity of bacterial wilt in solanaceous plants were also conducted. The data show that disease rating of bacterial wilt in three treatments - (i) inoculated with root-knot or lesion nematode and 1 month later with the bacteria; (ii) inoculated with the bacteria and 2 weeks later with the nematodes; (iii) inoculated with nematode and bacteria simultaneously - was higher than inoculated with bacteria only. This conclusion showed that the disease complex between plant-parasitic nematodes and Ralstonia solanacearum could increase disease severity and reduced the resistance of bacterial wilt-resistant solanaceous plants in Taiwan.

References
1. Hayward AC, 1994. Bacterial Wilt: The Disease And Its Causative Agent, Pseudomonas solanacearum. pp. 9-24.
2. Sitaramaiah K, Pathak KN, 1993. Nematode Interactions. pp. 232-250.