A Study of Some Factors Influencing Germination of the Spores of Phyllosticta Solitaria

Abstract

Studies were made of the effect of various factors on germination of spores of Phyllosticta solitaria E. & E., taken from culture and from bark cankers. Spores taken from cultures at least foq,r weeks old were found to germinate best. Good germination was observed at the end of twenty-four hours after sowing but higher counts were. obtained when the spores were examined on the second day. Thc spores were found to germinate readily in distilled water. The minimum, optimum, and maximum temperatures for spore germination were found to be 5?C., 21?-23?C., and 39?C. respectively. Spores from pycnidia in bark cankers showed consistently lower germination than spores from culture; however, the minimum, optimum, and maximum temperatures for germination were the same in both cases. When, instead of percentage germination, average germ-tube length (taking into account both germinated and ungerminated spores) was used as a measure of viability, the results agreed, in nearly every case, with those obtained by the former method. There was an increase in spore germination in bark decoction and potato-dextrose broth as compared with distilled water. There was a slight increase in Coons' solution but tap water, rain water, apple fruit juice, and K. U. solution had an inhibitory effect. Of variotls tissues place(t near the germination drop, bark tissue acted as a stimulant, apple bark being the most effective. Orange tissue (rind and fruit tissue), onion scale and shoot, and apple fruit tissue inhibited spore germination somewhat. Spore germination was not appreciably affected ny varying degrees of light. Although spores formed in culture will germinate almost as soon as they are formed they germinate best when ten days or two weeks old. Thus it seems there is an interval between morphological and physiological maturity of spores formed in caulture as well as in nature.