Two major findings relating to the breeding system ofSenecio vernalisfrom Israel are reported. First, isolation experiments failed to confirm the existence of a widespread, truly self-compatible and predominantly self-pollinating breeding system in Israeli populations ofS. vernalis.However, a singleS. vernalisplant derived from a natural stand at Jerusalem was found to be self- compatible and strongly self-pollinating. In its progeny, there were signs of inbreeding depression commonly associated with selfed offspring of outbreeding species. Selfing ability ratios in this progeny indicate a single dominant gene for selfing ability inS. vernalis.The implications of these observations for the origin ofS. vulgarisare briefly discussed. Second, the occurrence of gynodioecy inS. vernalispopulations from Israel is reported. Although male sterile plants are recognizable by the complete absence of pollen on their exposed stigmas, there probably exists a large amount of variation within and between plants for pollen production. Infertile pollen grains of male steriles differ in size, shape, and sculpturing from those of hermaphrodites. At the Mt. of Olives, in Jerusalem, the frequency of male steriles was found to be 9.1. There is some preliminary evidence for differences in floret (= ovule) number between the two gender types. Although the inheritance of male sterility appears to be predominantly cytoplasmically controlled, additional mechanisms restoring male fertility have to be postulated to account for the data observed in one of the crosses. The male sterility system inS. vernalisshould therefore be referred to as #x201C;nuclear-cytoplasmic.#x201D;
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