A COMPARISON OF THE VEGETATIVE GROWTH OF MALE-STERILE AND HERMAPHRODITIC LINES OF PLANTAGO-LANCEOLATA IN RELATION TO N SUPPLY

Gynodioecy is a dimorphic breeding system in which hermaphrodites coex ist with male steriles in natural populations. Theoretical models pred ict that without any compensation in female fitness, male steriles wil l quickly disappear from a population. The amount of compensation requ ired depends upon the mode of inheritance. In this study we investigat ed whether performance, during early vegetative growth, could play a r ole in the maintenance of male steriles in populations of gynodioeciou s self-incompatible Plantago lanceolata. This was accomplished by comp aring the growth of the predominant male-sterile type from a natural p opulation with two hermaphroditic types. One of the hermaphroditic typ es differed from the male sterile only in nuclear genome, having the s ame type of cytoplasm. The other type was nuclearly nearly isogenic, b ut had a different cytoplasm. Plants were grown under controlled condi tions, either in near-optimal hydroponic solutions, or in a range of N -supplies on sand. A detailed growth analysis was carried out, and the relative growth rate (RGR) Of each type was analysed into its underly ing components, the net assimilation rate, the leaf mass ratio and the specific leaf area. No difference between the sex types in relative g rowth rate was found and, in the components underlying the RGR, only a few small differences were detected. In none of the growth parameters examined did the male steriles differ from either hermaphroditic type . Differences in plant growth related to N-supply, differences in grow th on hydroponics compared with sand culture, as well as the maintenan ce of male sterility in populations of P. lanceolata are discussed.