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 coexist with male steriles in natural populations. Theoretical models predict that without any compensation in female fitness, male steriles will quickly disappear from a population. The amount of compensation required depends upon the mode of inheritance. In this study we investigated whether performance, during early vegetative growth, could play a role in the maintenance of male steriles in populations of gynodioecious self-incompatible Plantago lanceolata. This was accomplished by comparing the growth of the predominant male-sterile type from a natural population with two hermaphroditic types. One of the hermaphroditic types differed from the male sterile only in nuclear genome, having the same type of cytoplasm. The other type was nuclearly nearly isogenic, but had a different cytoplasm. Plants were grown under controlled conditions, 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 underlying components, the net assimilation rate, the leaf mass ratio and the specific leaf area. No difference between the sex types in relative growth 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 growth on hydroponics compared with sand culture, as well as the maintenance of male sterility in populations of P. lanceolata are discussed.