Seed production and seed germination of Amsinckia hispida

Abstract

Amsinckia hispida is a serious annual weed of cereal culture in north-western Victoria. Individual plants produce seed for up to two months in the spring and this provides a range of seed maturity that is reflected by a gradual build-up of germinability in the following autumn. In addition the seed has an optimum constant temperature for germination of 13¦C (48¦F) and responds markedly to a period of cold treatment. These three features act together to produce the series of Amsinckia populations which are characteristic of its autumn germination behaviour in north-west Victoria. Seeds which germinate early are responsible for infestations in the pasture phase and those which germinate later are not controlled by pre-sowing cultivation and remain to germinate within crops. The response of Amsinckia to environmental factors is such that these plants which germinate late within wheat crops have an extended rosette period and are highly competitive.