EARLY STAGES IN THE FORMATION OF INTERNAL BARRIERS TO GENE EXCHANGE BETWEEN DIPLOID SPECIES OF SOLANUM

Abstract

Grun, Paul. (Pennsylvania State U., University Park.) Early stages in the formation of internal barriers to gene exchange between diploid species of Solanum. Amer. Jour. Bot. 48(1): 79–89. Illus. 1961.—Internal barriers restricting development of F1 hybrids in crosses among closely related diploid species of Solanum belonging to the series Tuberosa and Commersoniana were studied to determine the early stages in development of barriers to gene exchange. Both of the parental series (species complexes) are native to South America, the Tuberosa occurring along the length of the Andes, while the Commersonia occur at lower altitudes in Argentina, Paraguay, and Bolivia. They are distinguished by a fair number of morphological characters. Following crossings between the species of each series and between species of the different series comparisons were made of the number of berries formed per attempted cross, seed per berry, percentage seed germination, and F1 vigor and pollen fertility. Although the species used were closely enough related that all could readily be hybridized, berry and seed set following crosses between species of different series were on the average lower than they were following crosses between species of the same series. These barriers are just forming and are expressed in a varying manner, so that there were significant differences between species of the same series, and even between clones of the same species in barrier expression. The barriers of some of the species were expressed only when they were tested as female or as male parent. The inter‐series F1 seeds germinated as well as did those of the parent species and the hybrids had a normal vigor and pollen fertility.