Abstract
The tropical grasses can hardly continue to survive throughout the winter season in northern area of Japan. In southwestern area, however, a few species of the tropical grasses have been introduced and improved because of the useful characteristics and the perennial behaviour. Recently various species of tropical grasses, such as a number of species of panic grass, have been introduced from tropical areas to reduce the seasonal fluctuation of pasture production. However, their winter survival or cold resistance has been little studied. It is essential for the more effective use and the improvement of the tropical grasses to know the specific and varietal differences of the capability of winter survival and cold resistance. This study was undertaken to establish the convenient procedures of testing the winter survival and cold resistance of the introduced tropical grasses and to evaluate the specific and varietal differences of the grasses. The results were as follows: 1) During the winter season at average temperature of 5℃, adult plants of panic grasses were transplanted from the field to the 1/5, 000 are Wagner's pots in the green house and observed their sprout. The sprout declined gradually with the duration remaining in the field. All the varieties which showed vigorous shoot growth in the sprout testing were able to survive in the field and sprout in April. 2) The sprout of the plants transplanted frow the field to the green house proportionally increased as increasing the response to triphenyl tetrazolium chloride (TTC) in the tissues of stem bases. 3) The specific and varietal differences in the resistance of the seedlings to the chilling damage at 5℃ apparently corresponded with the capability of the winter survival of the plants in the field. 4) The appearance of the chilling damage on the seedling was modified by the leaf stage, the duration of exposure to chilling temperature and the growing temperature prior to the chilling treatment. 5) From assessment of the above testing, all the evaluated varieties of switch grass and giant panic grass, and klein grass introduced from U.S.A.-all showed the same capability of winter survival and cold resistance as dallis grass and bahia grass which could survive throughout the winter season in Nasu, Tochigi Pref.. A few varieties of coloured Guinea grass, such as N-780 and Singapore strain, exhibited comparatively high winter survival, whereas these grasses could hardly survive throughout the season. Morocco, Bambatsi and Karahari strain of coloured Guinea grass continued to survive only 2 months under the field condition in this experiment. All the other species, such as Makarikari grass, Kablabla grass and Guinea grass, hardly survived.
