Genotype variation in sensitivity to daylength and air temperature of Glycine Max. (L.) Merrill : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University

Abstract

Thirteen cultivars of Glycine max. (L) Merrill, each representing one of the maturity groups from 00 to 11 *USA classification or its estimated equivalent, were grown under field conditions at Massey University, Palmerston North, New Zealand. The cultivars were sown at 14 day intervals from the 12th October 1974, to the 18th January 1975, inclusive. Daily plant observations were made to record the dates of seedling emergence, flowering onset, pod emergence, cessation of flowering and pod maturity. With the maturity groups 1 and 4 cultivars, a separate apical bud dissection study was made of the morphological changes occurring during floral initiation and subsequent bud development. Multiple regression analysis was used to study the effects of daylength and air temperature on the phasic growth patterns of each of the thirteen cultivars. In all cultivars, germination increased at an exponential rate as air temperatures rose from 12°C to 21°C. Temperatures above 21°C inhibited germination in the maturity groups 2, 4, 6 and 8 cultivars and were inhibitory above 25°C for all other cultivars. In all cultivars, transition from the vegetative to the reproductive state was accelerated by declining daylengths and rising temperatures. Sensitivity to daylength during the pre-flowering phase increased with genetic lateness of maturity among the cultivars. From the apical dissection studies, daylength and temperature were shown to affect both rates of floral initiation and subsequent bud development. In the absence of an adequate daylength stimulus, plant age became the main determinant of the rate of floral development. Pod emergence showed a negative response to daylength in the maturity groups 00 to 5 cultivars and a positive response in the groups 8 to 10 cultivars. Temperature was the main determinant of podding duration, rates of pod development decreasing with decline in temperature as the season progressed. Both flowering and podding duration increased with decline in daylength. The photoperiod response during these growth phases was not associated with genetic lateness of maturity among the cultivars tested.