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Developmental Periods in Soybean: Photoperiod-Sensitive x Insensitive Crosses Evaluated at Diverse Latitudes

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011, and Dep. of Agronomy and Soils, Univ. of Puerto Rico, Mayaguez, PR 00708

D. E. Green

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011

C. -S. Chang

Hualien District Agric. Improv. Stn., Taiwan, ROC 97309

R. M. Shibles

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011

*Corresponding author.

Selection for long duration of seed-filling period (SFP) in segregating soybean [Glycine max (L.) Merr.J populations may be a way to increase seed yield. Tbe objective of tbe study was to assess the relative effectiveness of selecting for SFP from tropical environments to develop lines for temperate locations in crosses of photoperiod insensitive x sensitive genotypes. A second objective was to determine if selection for longer SFP is possible without delaying date of physiological maturity (R7). Three populations were developed by crossing a photoperiod-insensitive genotype of Maturity Group (MG) HI to photoperiod-sensitive genotypes of MG I, II, And III. Random F4-derived lines were evaluated at Ames, IA, at Isabela, PR (under both natural and lighted environments), and at Hualien, Taiwan, for days from emergence to beginning flowering (Rl), rapid seed-filling (R5), R7, SFP, and reproductive period (RP). Significant (P < 0.05) differences among lines, environments, and environment x genotype were observed. Phenotypic and rank correlations of Stages Rl, R5, and R7 between environments ranged from 0.22 to 0.83. The range in correlation coefficients for SFP and RP was from 0.06 to 0.62. It is possible to select lines for duration of SFP at PR environments in plantings under natural daylength or under lights. Selections in PR included genotypes ranked in the top 33% at the IA location, and generally included at least one of the five topranked lines. Lines may also be selected with a desired combination of duration of SFP and number of days to reach Stage R7.

Received for publication September 11, 1989.