• Korean Journal Plant Pathology
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• v.3 no.2
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• pp.131-136
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• 1987

Rates of lesion development over time and disease gradients over distance for blast disease on the two rice varieties, Brazos and M-20 1 were significantly affected by two different cultural conditions, upland and flooded conditions. Flooding rice field plots lowered the rates of lesion increase and flattened the disease gradients for both varieties. Despite absence of statistically significant differences in the rate of lesion increase between four sampled distances from infection focus, rate of lesion development tended to be slightly greater as distance from the infection focus increases. Rate of lesion increase was greater with more susceptible variety M-201 than with Brazos. Disease gradient was steeper for M-201 than for Brazos. As blast disease progressed, disease gradients became flattened regardless of variety due to the infections originated from secondary foci. Between two empirical disease gradient models examined, Kiyosawa & Shiyomi model was fitted better over Gregory model. Rates of blast isopath movement under upland conditions were calculated as approximately 0.2m/day and 0.4 m/day for Brazos and M-201, respectively. The results in this study suggest that differences in varietal resistance to blast could be detected by measuring disease gradient as efficiently as by measuring infection rate.

• The Korean Journal of Ecology
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• v.6 no.1
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• pp.45-54
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• 1983

A distribution map of black pine, Pinus thunbergii, in south Korea was prepared through field surveys. According to Mirov(1967), the range of black pine is limited in east Asia, Japan and Korea; its northern limit is at about 41。34' north and its southern limit on Takara island, south Kyushu, at 29。 north. According to the present map, its northern limit coincided with the isopath of warmth index 100 by Yim(1977). The density of pine in grid mesh, about 4 km * 4 km, was higher at costal area than that in inland area, and it was also higher at sea side slope than the opposite slope of the same mountain. This suggests that the ecological distribution of black pine is greatly affected by salt content of the soil or the optimal range of summed temperature for the pine growth.