STERILITY IN RELATION TO HORTICULTURE

Abstract

The sterility problem in horticulture will be discussed from the standpoint of those factors which limit the crop. Since most of the principles involved are encountered in pomology, the discussion will be limited to this field. Recent investigations have dealt with many of the causes of what the fruit-grower designates as a crop failure. In the broader sense the sterility problem has its setting in the factors which influence the initiation and formation of fruit buds as well as in those which bear upon the set of fruit. It will be evident that, in all of those fruits in which the edible portion includes a ripened ovary, bloom must precede the production of fruit. Let us for the moment, then, keep in mind the point of view of the horticulturist in analyzing the causes which bear upon the set of fruit. Before taking up the discussion of the individual fruits, emphasis will be placed for the sake of clearness upon some general considerations. First: The variety is the unit in horticulture. Varieties may be discussed in the classroom and in the laboratory in terms of species, but in the orchard and on the market the variety is the unit. The present tendency, however, in breeding horticultural plants to make so many interspecific crosses will tend to bring the characteristics of the species to the foreground, and at the same time, especially in wide crosses, to increase the difficulties in the setting of fruit because the hybrid condition may have an important bearing upon the formation of pollen and embryo sac. Second: The ratio between the number of flowers produced and the number of fruit to set, or to mature, varies in the different fruits. In the apple or plum, for iftstance, a set of five to ten percent of a full bloom is sufficient for a crop. It would be physically impossible for the tree to mature a fruit for each flower in the apple, pear, plum, or peach. On the other hand it is possible for all the pistils in the grape, raspberry, blackberry, strawberry, or currant to set and mature. Likewise, the number of seeds necessary for fruit development varies. Some fruits are seedless, like the banana and the seedless grape; others, like the peach or plum, require a single seed for development; while in the apple and pear the number of seeds present in ripe fruit differs with the variety and also from season to season. In the strawberry or raspberry, where the development of the edible fruit reaches perfection only when a high percentage of the achenes or drupelets set, many more ovules fail to develop in marketable fruit than 1 Read in the symposium on Sterility in Plants, at the joint meeting of Section G of the American Association for the Advancement of Science, the Botanical Society of America, and the American Phytopathological Society, at Cambridge, December 27, 1922. 474