SUMMARYInheritance of male sterility has been studied in Plantago lanceolata. Crosses between plants, obtained from a 50 m2 area, yielded the entire array of possible sex phenotypes. Emphasis is put on nuclear inheritance of two nuclear-cytoplasmically determined male sterility types. In both types multiple interacting genes are involved. For MS1 a combination of two recessive and three dominant male sterility genes is proposed, for M52 three recessives. These are minimum estimates as the exact numbers could not be determined. One of the loci for MS2 is probably linked to the self-incompatibility locus. Not all results can be explained this way, which emphasizes the complexity of nuclear inheritance. Intermediates between the completely male steriles of both types and hermaphrodites constitute two continuous series, each consisting of multiple genotypes with overlapping phenotypes. Segregation patterns indicate genetic determination by incomplete dominance at the male sterility loci. A third male sterility type (MS3) is described whose expression appears to be independent of plasmon type. Preliminary results indicate two duplicate recessive male sterility genes.The stability of the complexity of nuclear inheritance for gynodioecy is discussed.
SUMMARYThe importance of the reproductive part of the life cycle for the maintenance of the gynodioecious breeding system in Plantago Ianceolata has been studied. Two male sterility types (MS 1, MS2). the corresponding partial male sterility types or intermediates (IN1, 1N2) and hermaphrodites (H) have been compared in four populations for seed production (ovule production [1 female fertility) and weight per seed. MS1 plants produce more and heavier seeds than hermaphrodites. MS2 produces more ovules than H, but it is partially female sterile, so that seed production does not differ significantly between the two phenotypes. Because MS2 in addition has a lower weight per seed, it has no advantage in reproduction via seeds over any other sex type. The results for the intermediate sex types indicate that overdominance at sex determining loci may be involved in the maintenance of MS2. Reproductive differences between genotypes within the H phenotype have been found in a cultivation experiment, in accordance with theoretical models, which concerns variation in pollen production, associated with plasmon type. The mechanism of partial female sterility is discussed. The observed differences between sex types are interpreted as pleiotropic effects of the male sterility genes. It is argued that while the differences between male steriles and hermaphrodites in sexual reproduction contribute to the maintenance of gynodioecy, they probably do not explain it fully.
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