Flowering responses of contrasting ecotypes of Poa annua and their putative ancestors Poa infirma and Poa supina

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 s uburban parks in Canberra had opposite daylength flowering responses across the range of temperatures tested (9-21 degreesC), one being a quantitative short-day (SD) plant with no response to vernalization, the other a quanti tative long-day (LD) plant with a quantitative vernalization requirement (w inter annual type). Variation in earliness of flowering within the former p opulation was shown to be genetically determined, and testing of selfed pro genies indicated that the population is an aggregate of several largely hom ozygous lines with divergent flowering responses. Two lowland populations f rom 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 quantitativ e SD plants with an obligatory plant vernalization or SD requirement for fl owering. Two populations of P, supina exhibited the same flowering response s as the alpine and high-latitude populations of P, annua with an obligator y plant vernalization or SD requirement for flowering. A combination of SD and low temperature (9-12 degreesC) for 8-10 weeks was optimal for inductio n and inflorescence initiation. On the other hand, P, infirma was found to be an early-flowering quantitative SD plant which flowered freely across th e range of temperatures (9-21 degreesC) as a typical summer annual. The exp eriments demonstrate that virtually any kind of photoperiodic and vernaliza tion responses can be found among populations of P. annua. These versatile flowering responses reflect the contrasting flowering responses of P. supin a and P. infirma, and add strong support to the hypothesis that P. annua ha s originated from these species. (C) 2001 Annals of Botany Company.