Abstract
Soybean (Glycine max (L.) Merrill)is a short day plant that flowers when days are shorter than the maximum critical value, and this period is specific for each genotype. Soybean sensitivity to photoperiodism determines the limits of the sowing period for a latitude and hinders adaptation to wider ranges of latitude. The long juvenile period (LJP), which delays flowering under short day condictions, has been identified in soybean cultivars. The introduction of the LJP characteristic in soybean has made its cultivation possible in regions with latitudes lower than 15 o . Knowledge of the controlling genetic mechanisms of this characteristic can help in the development of soybean genotypes for lower latitudes with greater adaptation to sowing periods within the same latitude. Some conclusions about the genetic LJP control in soybean were reached from the present review: a) plants with LJP have a lower development rate for flowering, resulting in the lengthening of the vegetative period; b) the LJP characteristic has a direct influence on plant photoreceptivity and flowering induction; c) the genetic control of flowering time in short days is determined by a different and independent genetic system from that which determines long day flowering time; d) late flowering under short day conditions is a quantitative characteristic controlled by recessive genes, and it is believed that one to five main genes control flowering. Genotypes with a single pair of recessive alleles did not have LJP.
Highlights
Many soybean development processes are related to daylight which has two important functions: soybean photosynthesis and photoperiodism
Soybean (Glycine max (L.) Merrill)is a short day plant that flowers when days are shorter than the maximum critical value, and this period is specific for each genotype
Some conclusions about the genetic LJP control in soybean were reached from the present review: a) plants with LJP have a lower development rate for flowering, resulting in the lengthening of the vegetative period; b) the LJP characteristic has a direct influence on plant photoreceptivity and flowering induction; c) the genetic control of flowering time in short days is determined by a different and independent genetic system from that which determines long day flowering time; d) late flowering under short day conditions is a quantitative characteristic controlled by recessive genes, and it is believed that one to five main genes control flowering
Summary
Many soybean development processes are related to daylight which has two important functions: soybean photosynthesis and photoperiodism. Bernard and Weiss (1973) were the first to detail the effect of main genes on the control of flowering time in soybean These authors studied the genotypes of individual plants from the F2 generation from crosses among isogenic lines in the Clark cultivar, to which the alleles that control maturity had been transferred. Aiming at selecting less sensitive soybean genotypes to photoperiodism to widen the sowing period, Toledo et al (1995) studied advanced lines derived from crosses involving cultivars with classic flowering (BR-13, FT-2 and BR85-29009) and cultivars with late flowering for short days (Ocepar8) under different sowing times (September, October, November) in Londrina, PR, Brazil. The variation amplitude of the same stage depends on temperature, daylight length, cultivar and other factors
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