Effects of temperature and photoperiod on growth and reproductive development in Hyparrhenia hirta

Abstract

Hyparrhenia hirta occurs naturally in the Mediterranean region and in the winter rainfall areas of South Africa, in association with temperate festucoid grasses. However, the temperature response curves, flowering behaviour, and widespread apomixis found in this species are more typical of other tropical members of the Andropogoneae. This residual tropical adaptation provides an explanation for the sensitivity of H. hirta to low temperature (below 15¦C) during seed germination, and especially during the seedling stage, which makes autumn establishment difficult in temperate climates. Also, the low seed yield is attributable to the high proportion (c. 50%) of male florets in the inflorescence, and the breakdown of both sexual and apomictic embryo sacs during development. A possible genetic approach to the improvement of both these characters, utilizing facultative apomixis, is discussed.