Characterization of Photothermal Flowering Responses in Maturity Isolines of Soyabean [Glycine max (L.) Merrill] cv. Clark

Abstract

All eight isolines of three maturity genes (E(1)/e(1), E(2)/e(2), and E(3)/e(3)) 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 degrees 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, e(1)e(2)e(3), e(1)E(2)e(3), e(1)e(2)E(3); (2) intermediate, E(1)e(2)e(3), e(1)E(2)E(3), and (3) most sensitive, E(1)E(2)e(3), E(1)e(2)E(3), E(1)E(2)E(3). Thus, in the Clark cultivar genetic background, E(1) induces greater photoperiod sensitivity but neither E(2) nor E(3) on their own have any effect. However, both E(2) and E(3) together induce photoperiod sensitivity comparable to that induced by E(1) alone. Furthermore, in addition to this epistasis, either E(2) or E(3) has considerable epistatic effect on E(1), 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.

Genetic and molecular bases of photoperiod responses of flowering in soybean

“…Clark NILs for the E1 , E2 , and E3 loci, Upadhyay et al (1994) found no effect of allelic substitutions at either E2 or E3 in an e1e1 background, whereas the effect of the E1 allele was marked and almost the same as that of the E2 and E3 alleles combined. Furthermore, the E2 and E3 alleles each interact positively with the E1 allele to enhance the photoperiod-sensitivity (Upadhyay et al 1994). A similar genetic interaction was observed in a combination of E4 with later-maturing genetic backgrounds (Saindon et al 1989b).…”

“…E1 has the largest effect on flowering (Bernard 1971, McBlain et al 1987, Upadhyay et al 1994). However, a near-isogenic line (NIL) of cv.…”

“…For example, the effects of some major genes such as E2 ( qFT2 ) and E3 ( qFT3 ) are weakened or masked in early-flowering genetic backgrounds, such as those conditioned by a recessive allele at the E1 locus (Upadhyay et al 1994, Watanabe et al 2004, Yamanaka et al 2001). The two QTLs qFT 2 and qFT3 , detected in a cross between a Japanese cultivar, Misuzudaizu, and a Chinese forage soybean line, Moshido Gong 503, exhibited only a small allelic effect on flowering time under an early-maturing background conditioned by the recessive allele at qFT1 ( e1e1 ), but the allelic effects became marked in a late-maturing background ( E1E1 ) (Yamanaka et al 2001).…”

Association mapping of loci controlling genetic and environmental interaction of soybean flowering time under various photo-thermal conditions

“…Soybean flowering time is regulated by both genetic and environmental factors [6, 7]. At least 11 major loci control flowering time and maturity in soybean, including E1 – E10 [8–17] and J [18].…”

“…In previous studies, short day and high temperature accelerated the process from emergence to first flowering of soybean, whereas long day and low temperature delayed flowering time [2, 3, 7]. The interaction between photoperiod and temperature also influences soybean flowering time [2, 3, 7]. However, the genetic mechanism of photo-thermal effects on soybean flowering time is not well documented.…”