Environmental control of reproduction in Themeda australis

Abstract

Seedlings and older plants of 30 ecological races of Themeda australis were grown under controlled conditions to determine the effect of day length and vernalization on their flowering and on the incidence of apomixis. The races ranged in origin from latitude 6°S. in New Guinea to latitude 43°S, in Tasmania.

One race from New Guinea and several from the Northern Territory behaved as strict short-day plants. The more southerly races, on the other hand, and several from north Queensland were long-day plants. In some, long days were required for both initiation and development of the inflorescence, in others apparently only for initiation. Some races required long days as seedlings, but not as older plants. Races from drier inland areas tended to be indifferent to day length in their flowering behaviour. At least four races from the colder areas responded to vernalization.

Both the sexual and the aposporous reproductive pathways are described. Two races were wholly sexual in their breeding system and two appeared to be almost entirely aposporous, but most were versatile, displaying both sexual and aposporous reproductive behaviour. In seven races there was some evidence that day length influenced the reproductive pathway, short days causing increased apospory in all cases, regardless of the day length requirements for flowering.