Gynodioecy in Plantago lanceolata L. III. Sexual reproduction and the maintenance of male steriles

Abstract

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.

Gynodioecy in Plantago lanceolata. VI. Functions of cytokinins in growth, development, and reproduction of two sex types

“…MS1 plants produced more and longer spikes, consistent with differences found in natural populations of this species (30). The relatively longer styles (measured at the same flowering stage) of the MS 1 plants may further increase female fecundity by enhancing the fertilization chance.…”

“…21). Our present results show that the fecundity differences between MS1 and HI plants, as found in natural populations (30,34), are also present under controlled conditions. The reported differences in vegetative growth characteristics could influence the survival rate of the sex types under competitive conditions.…”

“…Each sterility type has a corresponding hermaphrodite type. Studies in the field demonstrated that the MS1 plants have more and longer spikes than H1 (hermaphrodites with the same cytoplasm as MS1) plants, and consequently form more seeds (30). The MS1 plants can also show a longer half-life time (34).…”

“…However, there are two reasons why this cannot be the only mechanism involved. First, some gynodioecious species are self-incompatible (e.g., P. lanceolata (30)). Inbreeding depression is unlikely to be involved here, and it has been argued that the male sterility genes themselves bring compensation with them through pleiotropic effects (31).…”

Modelling the maintenance of male-fertile cytoplasm in a gynodioecious population

“…Biologically, a CMS cost would mean that cytotype identity could affect female fitness, which has indeed been shown in Plantago lanceolata (Van Damme, 1984) and Silene vulgaris (McCauley and Olson, 2003). The difference in fitness is expected to be greater between CMS and a 'normal' cytoplasm (than between CMS cytotypes).…”