Sugarcane mosaic disease has been recently prevailing in Nansei Islands in Japan. The present work in an attempt to evaluate resistance of sugarcane varieties to mosaic disease under field condition for 8 years, and the following results were obtained.
1.Natual infection of mosaic disease on sugarcane was affected by various factors such as year, field location, cultivation type, fertilizing level and variety. Analyses of variance for cultivation factors showed only effect of variety was highly significant but fertilizing level and cultivation type were no significant effect on mosaic infection.
2.Correlation analysis of mosaic infection on the selected clonal lines revealed highly positive between years and cultivation types under higher infected condition. When more than 10% average infection of the lines, it is possible to estimate varietal difference of mosaic disease resistance.
3.Annual fluctuation for mosaic infection on 5 cultivars demonstrated varietal infection was stable in proportion with yearly deviation. Logical value of infection percentage on each cultivar was estimated by mean of regression equation to infection of NCo 310, the most susceptible variety.
4.Mosaic disease resistance of the standard varieties were classified as follows basing upon the ISSCT scale. Highly resistant (1) : KF69-101, Resistant (3) : L 60-14 & NiN 2, Moderate (5) : Ni 1, Susceptible (7) : NCo 310
5.The clonal lines were also evaluated on mosaic disease resistance comparing with the standards as shown in Table 9. No immune variety was found so far as the materials, however, highly resistant variety was proved to escape from practical infection under field condition and to be utilized as gene source in the resistance breeding.
6.Serious prevailing of mosaic disease on Nansei Islands is mainly due to wide and long term occupation of single genotype, a susceptible cultivar NCo 310. Therefore, it is important to promote resistance breeding, which methods were discussed.

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The mechanism of salt tolerance in rice was investigated by comparing two indica varieties differing in salt sensitivity; Nona Bokra as a salt tolerant variety and Chiem Chanh as a salt sensitive one. The growth of Nona Bokra after salinization was much greater than that of Chiem Chanh. The photosynthetic rates of both varieties declined with increased leaf Na⁺ content. The leaf Na⁺ content of Nona Bokra did not increase very much after salinization with 150mM NaCl, and remained relatively low at high saline levels. The results obtained suggest that Nona Bokra, which is salt tolerant, could maintain in low Na⁺ content in the most active leaves for a long time at relatively high NaCl concentration in culture solution and consequently could maintain high photosynthetic rate.

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