The long-juvenile (LJ) trait in soybean [Glycine max (L.) Merr.] has been defined as delayed flowering under short-day conditions. The genetic control of this trait remains ambiguous in the literature, and this study was undertaken to determine the genetic control of the LJ trait. Three field experiments were conducted between 1984 and 1991. In the first experiment, segregation patterns of the LJ trait were examined in six F 2 populations from crosses between conventionaljuvenile (CJ) lines and P1 159925 (source of the LJ trait). Results indicated that the LJ trait is controlled by a single recessive gene influenced by the genetic background in which it occurs. In the second experiment, the confounding effect of other genes segregating for flowering was eliminated by studying F 2 populations from crosses between members of four pairs of near isogenic lines primarily differing in the presence of the LJ trait. A total of 1954 F 2 plants were observed from eight crosses. Within all F 2 populations, the segregation patterns for the LJ trait had a good fit to a 3:1 ratio of CJ/LJ expected for a single recessive gene. The dominance relationship of the alleles was examined in the third experiment using Fj and F« families developed from seven different crosses. Results indicated that the J allele, which conditions the CJ phenotype, is nearly completely dominant. Our results indicated that the LJ trait is controlled by a single recessive gene and the symbol J/j has been assigned for the alleles conditioning the flowering response (/-, CJ, andjf, LJ). T HE LONG-JUVENILE (LJ) TRAIT results in delayedflowering under short-day conditions. It was identified by E.E. Hartwig in a plant introduction designated as P1 159925 (Hinson, 1989). When sown in May at latitudes near 33°, P1 159925 flowered as a Maturity Group VIII genotype; however, in August sowings (shorter days), it flowered more like a Maturity Group IX or X genotype (Hartwig and Kiihl, 1979). Normally Maturity Group Vin genotypes grown under short days flower in about 30 d, but under the same conditions, P1 159925 flowers in about 50 d (Hartwig and Edwards, 1986). The descriptive phrase delayed flowering under

Foliar fertilization (FF) was reported to increase seed yields of soybean [Glycine max (L.) Merr.] in field experiments in Iowa, but yield increases were not consistent. The researchers hypothesized that FF should minimize nutrient depletion from leaves during seed development, and thereby delay the resulting decrease in leaf photosynthesis. To test this hypothesis, we conducted a field experiment in 1976 to determine the effect of FF on leaf element concentrations, gross leaf photosynthesis (Pg), and soybean seed yield. Five weekly foliar sprays were applied during the seed‐filling period of ‘Bragg’ soybean grown at Gainesville, Florida on Kendrick loamy sand (loamy, siliceous, hyperthermic grossarenic paleudult). At weekly intervals, we sampled upper leaves and total canopy leaves and analyzed them for N, P, and K, and measured Pg of upper leaves in mid‐day sun with a 14CO2 gas flow technique. Foliar applications of N, P, K, and S increased the N, P, and K concentration of total canopy leaves from 3.28, 0.24, and 0.92% to 3.48, 0.29, and 1.32%, respectively. FF significantly increased upper leaf Pg only at two late sample dates when seed growth was nearly complete and most leaves had already senesced and dropped. Even though nutrient concentrations were increased, FF did not significantly affect yields nor did it extend Pg duration or delay maturity. Treated soybeans yielded 3617 kg/ha compared to 3825 kg/ha for control soybeans. Leaf Pg and concentrations of N and P in leaves progressively decreased during seed‐filling until maturity but K did not decline. Leaf Pg was positively correlated with N (r = 0.87) and approached zero at approximately 1.75% N, a concentration similar to that of senesced, recently abscised leaves. Maximum Pg was predicted at 4.6 to 6.0% leaf N. Leaf Pg and percent P were also positively correlated. The relationship of Pg to leaf N during N removal from leaves can potentially be used to model photosynthetic decline during seed‐filling.

Temperature and photoperiod are important determinants of the time from emergence to flowering in soybean [Glycine max (L.) Merr.]. A linear and a logistic model have been developed independently for describing the development rate to flowering (a high development rate means a short time to flowering). Field experiments on Arredondo fine sand soil (loamy, siliceous hyperthermic Grossarenic Paleudult) at Gainesville, FL, during 3 yr using a range of sowing dates in each year provided data to evaluate each model. In the first 2 yr, 13 cultivars were grown from 17 sowing dates. The linear model was found to represent adequately these 2 yr of data, but the logistic model was somewhat superior for 12 of the 13 cultivars. The coefficients derived for each model from the first 2 yr of study were used to predict flowering date in the 3rd yr. Both models gave accurate predictions of flowering date, although the larger discrepancies between predictions and observations were obtained with the linear model. Assuming an adequate data base to evaluate the coefficients in each model, either model was able to predict soybean flowering date.

OMPETITION stress is exerted on a plant by the spatial arrangement and phenotype of surrounding plants. The extent to which competition stress influences a plant character is an important consideration in selecting for that character in a breeding program. If a predetermined plant spacing can be identified at which competition stress has a negligible effect on genotypes, relative to their performance in drilled rows, effective selection may be practiced on an individual plant basis with considerable economy in time and field space. Plant spacings much wider than commercial planting rates would be desirable to facilitate plant measurements and identification and to provide adequate planting seed for progeny testing. Heritability estimates summarized by Johnson (9) indicate that spaced F~ plants are frequently poor indicators of their genetic potential for yield, are better indicators of their genetic potential for chemical composition, and are very reliable indicators of some agronomic characters. Differences in competition stress are undoubtedly one reason for the failure of spaced plants to indicate the relative performance of their less heritable characters at commercial planting rates. A differential response of genotypes to spacings was obtained for yield (~0, 11) and number branches (10)at within-row spacings likely to be encountered in commercial production. Border-row competition resulted in significant yield differences (5, 6) but had appreci.able effect on chemical composition of seed. Differences m response to photoperiod are likely to be very important since plant development is controlled to a considerable extent by the response of a plant to photoperiod (i, 2, 4). Limitations imposed by the necessity of small plot size for individual plants are obvious but have no satisfactory solution. This paper presents the results of an experiment conducted at Gainesville, Florida, in 1955 and 1956 to study the effect of competition on yield, chemical composition of seed, and agronomic characters of soybeans and to determine if a within-row spacing could be identified at which the effects were negligible.

Soybean [Glycine max (L.) Merrill] lines selected for differences in oil percentage from BC1 and BC2 populations were evaluated for seed yield, oil percentage, and protein percentage. Selection on the basis of oil percentage was effective in obtaining lines distinctly different in protein percentage.High‐protein lines averaged lower yields than did high‐oil lines. All BC1 lines averaged lower in seed yield than BC2 lines. Evidence is presented to show that factors other than chemical composition have influenced the seed yield level of the lines selected.