콩 시스트선충병과 미이라병의 합리적 방제기술 연구 = Studies on Effective Control for Cyst Nematodes and Phomopsis Seed Decay of Soybeans

다국어 초록 (Multilingual Abstract)

Soybean cyst nematode(SCN) (Heterodera glycines) and Phomopsis seed decay (Phonropsis longicola and Diaporthe phaseolorum var. sojae) are reported to occure at relatively high frequency from all over the soybean growing areas in Korea Severe damage in soybean production due to these diseases could be possible if proper control strategies are not established in the near future. In order to reduce the possibility of pathogenic differentiation of SCN populations, use of tolerant cultivars has been suggested. Tolerant cultivars may support a large number of nematodes with only limited injury to host plants. Therefore, use of tolerance is a method to limit soybean yield losses from SCN without providing directional selection pressure to SC1V populations for development of more aggressive races. Comparison of yield lasses of different soybean lines due to SCN is presently the only way to select tolerance to SCN. However, it usually takes more than two years and a great deal of labor to conduct yield loss studies in the field, which is not efficient enough to be adopted in a breeding program. As an efficient method to select soybean lines with tolerance to SCN, relative sizes of syncytia within the stelar region of soybean root tissues at the infection sites of SCN were compared between soybean lines in this study. When 'Bangsa' and 'SNUA' soybeans seedlings were compared, the relative size of the stelar region which was replaced $quot;by syncytia was 29.4% and 8.3% for `Bangsa' and `SNUA', respectively. Longitudinal translocation of water and nutrients through the stelar region of the soybean root tissues should be greatly inhibited when larger area of the stelar region was replaced by the syncytia. Since the two cultivars showed approximately the same degree of susceptibility to SCN when compared based on the number of cysts reproduced after inoculation to seedlings of the two cultivars in the greenhouse, 'SNUA' may be considered to be more tolerant to SCN than `Bangsa'. In this study, it took only 1-2 months to obtain quantitative data on toe relative size of syncytia within the stelar region after planting soybean seeds in pots in the greenhouse to tolled root samples with cysts for light microscopy. As for Phomopsis seed decay, soybean seed infection rates which were surveyed at 53 locations in Korea in 1988 indicated that the disease is widespread throughout the country at the average frequency of 2.7% with the range of 0.1-7.37% from samples of yellow soybean seeds. Use of dean seeds, crop rotation and fungicide spray have been suggested as effective control strategies for Phomopsis disease. Although a field experiment which was conduced in 1989 showed effectiveness of clean seeds and crop. rotation to control Phomopsis disease, it is not easy to obtain clean seeds and to maintain rotation system with other profitable crops at a long-term intervals of more than 3 years. Also, intensive use of fungicides is not economical considering crop value of soybeans. Consequently, the maximum economic profit can be achieved through planting soybean seeds as clean as possible under a short-term interval crop rotation system and spraying fungicides only when it is necessary and economically justifiable. A study to develop a forecasting system for Phomopsis seed decay is being conducted using the pod test at various growth stages of soybeans The objectives of this study are to determine time periods of pod infections that lead to seed infection in the later season and to evaluate effectiveness of fungicide sprays based forecasting. Also, dynamics of epiphytic populations of an antagonistic bacterium, Pseudomonas acruginosa, is being studied to evaluate possibility of using the bacterium as a biological control agent for Phomopsis disease.