Experimental studies of self-incompatibilities in fertilization

Abstract

The phenomenon of self-incompatibility in the fertilization of hermaphrodites is well illustrated by conditions existing in the common chicory plant (Cichorium Intybus). The flowers are perfect, they are anatomically all alike, the flowers are open only for a short time so that pistils and stamens are ready for pollination at the same time, and the parts are decidedly adapted for self-pollination, and yet when controlled self-pollinations are made many plants, set no seed. Many cross-pollinations are also incompatible, but both pollen and pistils will function in certain crosses. The inability to set seed to self-pollination (or cross-pollination as well) is here best described as due to some sort of physiological incompatibility operating between sex organs (including sex cells themselves) that are fully formed, anatomically perfect, potentially functional and of simultaneous development.

Studies in chicory have been pursued by the writer during the past six years. Nearly 2,000 plants (all but the first crop were pedigreed) have been studied and controlled pollinations made of heads comprising a total of over 450,000 flowers. There is thus available inore data on self-compatibility for this plant than for any other or perhaps for all other species in which the phenomenon has been studied. Publications giving data in detail and conclusions for results obtained previous to 1917 together with discussion of literature and theories have already been made. A brief summary of results and conclusions can be made here, however, as follows :

I. The results obtained with chicory indicate (a) that selfand cross-incompatibilities are strongly in evidence in this species; (b) that self-compatible plants may arise sporadically from parents that are self-sterile even after three generations of self-incompatible ancestry; (c) that the progeny of such plants do not breed true to this character; (d) that the degree of self-compatibility varies greatly; (e) that selection for high degrees of self-fertility continued for four generations has not been effective in isolating a completely self-fertile strain.