Gibberellin substitution for long day secondary induction of flowering in Poa pratensis

Plants of Poa pratensis cv. Holt initiate inflorescence primordia when exposed to short days (SD) and low temperature, but require a secondary induction by at least 4 long days (LD) for further inflorescence development and stem elongation. Single or double applications of 10 mu g per plant of gibberellins A(1), A(3), A(5) and 16,17-dihydro A(5) (DHGA(5)) induced in florescence development in a high proportion of plants in SD, but only if the plants were detillered to a single stem. Exposure to 2 LD cycles did not cause heading and flowering alone but enhanced the effect of exogenous gibberellins (GAs), bringing flowering to 100%. GA(5) and DHGA(5) were less effective than GA(1) and GA(3) in SD, especially with double applications, but were more effective than GA(1) and GA(3) when given together with 2 LD. The GAs had differential effects on vegetative growth and flowering, GA(5) and DHGA(5) causing much less leaf and stem growth than the other two GAs, Marginal induction, whether by LD or GA application, resulted in a high proportion of spikelets with viviparous proliferation. Thus, whereas GAs are inhibitory to the primary induction by SD, they can replace secondary induction by LD when vegetative growth is limited.