Environmental and Genetic Control of Reproduction in Danthonia caespitosa Populations

Abstract

Seedlings and older plants of five populations of Danthonia caespitosa from south-eastern Australia were grown in controlled environments and in a transplant garden to determine the effect of day length, temperature, and vernalization of floral initiation and inflorescence development. The populations were selected from widely separated sites which spanned the latitudinal range (31-42°S.) for the species and extended from a hot, semiarid environment in the north to a relatively cool and moist temperature environment in the south.

Examination of herbarium specimens indicated that seed set could occur as early as mid September at the northern limit for the species and not before mid January at the southern limit (Tasmania). In a uniform transplant garden located at Deniliquin (latitude 35° 23′S.) plants from the northern site reached anthesis 4 weeks earlier than plants from southern sites.

Controlled environment experiments revealed that D. caespitosa is a long-day plant. Northern populations required a 9 . 5 hr day length or longer for floral induction compared with 11 hr or longer for southern populations. The number of days in inductive conditions (outside, day length 13.5 hr) required for floral initiation was 5-7 for the three most northern populations and 21-25 days for the two southern populations. Inflorescence development (initiation to flag leaf stage) was considerably slower in southern populations.

All but the most northern population responded to vernalization. Flowering was earlier in temperatures that were optimal for plant growth. At high temperatures (36/31°C day/night) flowering was not significantly delayed for the three most northern populations, but was for the two southern populations, and florets contained caryopses in only the three northern populations.

These results suggest that in cool and moist temperate habitats reproduction of this species is programmed by day length and temperature effects on floral initiation and development to coincide with a predictable growing season, whereas in hot semiarid habitats this control is relaxed, which permits opportunistic reproduction whenever soil moisture and temperature permit growth.