Flowering Responses of Contrasting Ecotypes of Poa annua and their Putative Ancestors Poa infirma andPoa supina

Abstract

Flowering responses of two Australian and six Norwegian populations of Poa annua and their putative ancestors P. infirma and P. supina were studied in controlled environments. The two Australian populations originating from suburban parks in Canberra had opposite daylength flowering responses across the range of temperatures tested (9–21°C), one being a quantitative short-day (SD) plant with no response to vernalization, the other a quantitative long-day (LD) plant with a quantitative vernalization requirement (winter annual type). Variation in earliness of flowering within the former population was shown to be genetically determined, and testing of selfed progenies indicated that the population is an aggregate of several largely homozygous lines with divergent flowering responses. Two lowland populations from southern Norway were both quantitative LD plants with no vernalization response, while two alpine snowbed populations from southern Norway and two high-latitude, subarctic populations from northern Norway were quantitative SD plants with an obligatory plant vernalization or SD requirement for flowering. Two populations of P. supina exhibited the same flowering responses as the alpine and high-latitude populations of P. annua with an obligatory plant vernalization or SD requirement for flowering. A combination of SD and low temperature (9–12°C) for 8–10 weeks was optimal for induction and inflorescence initiation. On the other hand, P. infirma was found to be an early-flowering quantitative SD plant which flowered freely across the range of temperatures (9–21°C) as a typical summer annual. The experiments demonstrate that virtually any kind of photoperiodic and vernalization responses can be found among populations of P. annua. These versatile flowering responses reflect the contrasting flowering responses of P. supina and P. infirma, and add strong support to the hypothesis that P. annua has originated from these species.