Abstract
Septoria brown spot closed by Septoria glycines is one of the most serious fungal diseases in soybean. Average yield reduction of 3 varieties for two years was $16.1\%$ by the septoria brown spot inoculation and $9.0\%$ by the natural infection as compared to fungicide-sprayed plots. Number of pods per plant and seed weight were significantly reduced while plant height, number of branches and number of nodes per plant were not affected. Yield reduction was positively correlated to the septoria brown spot severity in all varieties examined. Correlation coefficient $(r=0.38^*)$ between yield reduction and area under the disease progress curve was higher than that (r=0.156) between yield reduction and Van der Plank's apparent infection rate. Potential effect of the septoria brown spot on the soybean yield reduction estimated with the area under the disease progress curve was expressed by the equation of Y=4.38+0.05X $(r=0.0696^*,\;df=25)$.
2년간에 걸쳐 조사한 대두의 수량감소는 갈색무늬병을 접종한 경우 농약 살포구에 비해 $15.7-16.4\%$ 감소 차였으며 자연감염의 경우에는 $8.2-9.2\%$의 감소를 나타냈다. 갈색무늬병의 감염은 초장, 주당절수(株當節數), 주당분지수(分枝數)에는 큰 영향이 없었으나 주당협수(狹數)와 종실중(種實重)에는 현저한 감소 현상을 보였다. 대두의 수량감소율을 갈색무늬병의 이병율과 정(正)의 상관을 보였으며 그 상관도는 Van der Plank's infection rate (0.156) 보다는 병 진전국선면적(AUBC) 과의 상관도가 높았다$(r=0.388^*)$. 병진전곡선 면적으로 표시된 갈색무늬병의 감염율과 대두수량 감소율과의 관계는 y=4.38+0.5X $(r=0.686^{**},\;df=25)$으로 나타났다.