Annals of Botany 74: 87-96, 1994
© 1994 Annals of Botany Company
Characterization of Photothermal Flowering Responses in Maturity Isolines of Soyabean [Glycine max (L.) Merrill] cv. Clark
Plant Environment Laboratory, Department of Agriculture, University of Reading Cutbush Lane, Shinfield, Reading RG2 9AD, UK
* Present address: Department of Agrometeorology, College of Agricultural Engineering, Jawaharlal Nehru Agriculture University, Jabalpur (Madhya Pradesh), India.
For correspondence.
Received: 26 July 1993 Accepted: 22 January 1994
All eight isolines of three maturity genes (E1/e1, E2/e2, and E3/e3) of soyabean [Glycine max (L.) Merrill] cv. Clark were grown in widely different combinations of photoperiod and temperature. Under the more inductive conditions, i.e. in a warm mean temperature (30 °C) when daylengths were less than the critical value (i.e. less than about 13 h), the isolines flowered at similar times (23–24 d). The responses of all isolines to temperature were also similar, if not identical. Increase in daylength above the critical photoperiod progressively delayed flowering until the time taken to flower (f) reached a maximum at the ceiling photoperiod. The relations between the rate of progress towards flowering (1/f) and photoperiod (between the critical and ceiling values) were linear. The coefficient characterizing the slope of the response (photoperiod sensitivity) varied amongst the isolines. These responses could be grouped into three categories of increasing sensitivity: (1) least sensitive, e1e2e3, e1E2e3, e1e2E3; (2) intermediate, E1e2e3, e1E2E3, and (3) most sensitive, E1E2e3, E1e2E3, E1E2E3. Thus, in the Clark cultivar genetic background, E1 induces greater photoperiod sensitivity but neither E2 nor E3 on their own have any effect. However, both E2 and E3 together induce photoperiod sensitivity comparable to that induced by E1 alone. Furthermore, in addition to this epistasis, either E2 or E3 has considerable epistatic effect on E1, further increasing photoperiod sensitivity. The effects of these genes and their epistasis were also reflected in the extent of the maximum delays to flowering which occur when the ceiling photoperiod is exceeded, and also possibly in earliness in circumstances when photoperiods were below the critical value.
Glycine max (L.) Merrill, soyabean, maturity genes, flowering, photoperiod, temperature