A DOMINANT GENE CONDITIONING EARLY FLOWERING AND MATURITY IN SOYBEANS

Inheritance was studied in natural variants of the soybean cultivar Parana, developed under photoperiodic conditions ranging from 13 h 31 min day light, at sowing, to 14 h 23 min, 59 days afterwards. Results indicated that early flowering and maturity are controlled by a single dominant gene. Natural mutations that originated cultivars Paranagoiana and SS-1 occurred at the same locus of cultivar Parana. It was not possible to determine if the recessive alleles of these mutant cultivars are different. The designation E6 was proposed for the alleles determining earliness in cultivar Parana, and e6 for the gene determining late flowering and maturity in cultivars Paranagoiana and SS-1, until the individuality of the alleles of Paranagoiana and SS-1 is confirmed.


INTRODUCTION
Soybean (Glycine max (L.) Merrill) acreage is expanding fast towards lower latitudes in Brazil.The cropping area is growing to the northern part of the country through regions above 20º latitude south, which has contributed towards maintaining Brazil as the second world soybean producer, responsible for more than 20% of world production.The time to flowering and maturity is important for adaptation to specific latitudes.
Five pairs of genes affecting flowering and maturity time in soybeans were described under long-day conditions.Bernard (1971) identified the genes E 1 /e 1 and E 2 / e 2 in isogenic lines of cultivar Clark.Buzzell (1971) described the gene E 3 /e 3 , whose dominant allele induces sensitivity to artificial fluorescent light in addition to determining late maturity.Buzzell and Voldeng (1980) identified the gene E 4 /e 4 , whose recessive allele results in insensitivity to daylength.McBlain and Bernard (1987) described the gene E 5 /e 5 .The dominant alleles of all five genes determine late flowering and maturity.
Genetic control of flowering and maturity time in soybeans under short-day conditions differs from that for long days, late flowering and maturity, being controlled by recessive alleles (Kiihl, 1976;Hartwig and Kiihl, 1979;Tisselli Jr, 1981;Toledo and Kiihl, 1982ab;Pípolo, 1996).These authors mention the presence of one to five major genes.Toledo et al., (1995) studying the time for flowering of lines derived from crosses among genotypes with normal juvenile period, BR-13, FT-2 and BR85-29009, and with long juvenile period, OCEPAR-8, under differ-ent seeding times, concluded that the photoperiodic sensitivity in these two types of genotypes is contolled by a unique genetic system.

MATERIAL AND METHODS
A study was conducted with F 2 and F 3 plants from a diallel cross, without reciprocals, involving the cultivar Paraná and its natural mutants, Paranagoiana, and SS-1.They were planted in Londrina, Paraná State, located at 23° 22' latitude south.From seeding date to the beginning of flowering of the earliest parent, the daylength ranged from 13 h 31 min to 14 h 19 min.The longest day was 14 h 23 min and occurred 59 days after sowing.
Paraná is a maturity group VI cultivar, tested as N59-6800 [Hill x (Roanoke x Ogden)].This line was introduced from North Carolina Experiment Station, USA, and was released in 1977.It has determined growth habit, white flowers, gray pubescence, yellow seed coat, and buff hilum (Kaster et al., 1979).Paraná was cropped for many years in the States of Rio Grande do Sul, Santa Catarina, Paraná, São Paulo, Mato Grosso do Sul, Minas Gerais, and Goiás and in Brasília, playing an important role in the development of soybean in these states (OCEPAR/ EMBRAPA, 1994).
Cultivars Paranagoiana and SS-1 resulted from natural mutations in time for flowering that occurred in the cultivar Paraná.Both cultivars present the same characteristics as Paraná, differing in the time to flowering and consequently in the characteristics resulting from later flowering, such as time to maturity, plant height, and grain yield (OCEPAR/EMBRAPA, 1988).In 1985, F 2 seeds provided by Romeu A.S. Kiihl, from the National Soybean Research Center, were seeded on October 23, using a randomized block design with split plots, with five replications.The plots received the crosses, while F 2 generations and the parents were seeded in the subplots.Emergence took place on October 29.Notes on the number of days to flowering and to maturity were taken for eight plants of each parent and 60 plants of each F 2 , in each replication.
The genotypes of F 2 plants were checked by the behavior of their progenies.For this purpose, a sample of plants was taken at random from each F 2 population.As the F 2 data indicated the presence of one gene, a limited number of F 3 lines were studied in each cross.
F 3 lines from each cross, along with the three parents used in the diallel, formed individual experiments.F 3 lines were sown to individual rows, without replications, and the parents were replicated from three to five times, depending upon the cross.Sowing was effected on October 24, 1986, and emergence took place seven days later.The dates to flowering (R 1) and to maturity (R 8) were recorded daily for 20 plants of each F 3 line, for 12 plants of each replication of parents in the crosses Paraná x Paragoniana and SS-1 x Paraná, and 40 plants of each F 3 line in the cross SS-1 x Paranagoiana.

RESULTS AND DISCUSSION
A bimodal distribution of F 2 plants was observed in the crosses Paraná x Paranagoiana and SS-1 x Paraná, both for flowering (Figure 1A and B) and maturity dates (Figure 2A and B), with a concentration of individuals towards the early parent (Paraná).It was not possible to separate, through phenotype, the dominant homozygous plants from the heterozygous ones.Nevertheless, for flowering, a frequency of 227 early and intermediate plants to 72 late ones was observed in the cross Paraná x Paranagoiana, and 223:75 in the cross SS-1 x Paraná.Such frequencies are in agreement with the proportion 3:1 (χ 2 probability = 0.71 and 0.94, respectively).Similar frequencies occurred for maturity (χ 2 probability = 0.17 and 0.51).These results show that the mutations originating cultivars Paranagoiana and SS-1 occurred in one gene and were recessive.Although this soybean crop  developed during days longer than 12 h, with photoperiods between 13 h 31 min and 14 h 23 min, early flowering and maturity were dominant.Results quite similar to the ones of the present study were also obtained by Gilioli (1979), in four crosses, under photoperiods of 13 h 21 min, by Moro et al. (1993) with the cross of Paraná x IAC-8 cultivated at 20º 45' latitude south, by Ray et al. (1995) in plantings with days with 13 h 10 min and 14 h 02 min of light, and by Vargas (1996) in crosses involving the cultivars Doko, BR-9 (Savana) and Davis, seeded at 23º 12' latitude south on October 14, November 25, and February 24.
In the cross SS-1 x Paranagoiana, in which the parents showed small differences in the number of days to flowering and to maturity, it was not possible to classify the F 2 plants into well-defined groups (Figures 1C and 2C).Unimodal distributions were observed, without transgressive segregation.
In the crosses Paraná x Paranagoiana and SS-1 x Paraná, the genotypes of F 2 plants that originated F 3 lines segregated in agreement with the theoretical proportion 1:2:1, showing that only one gene differs in each parent compared to the other (Tables I and II).When the plants of the 11 F 3 heterozygous families of the two crosses were pooled into early and late classes, they gave a good fit to the expected 3:1 ratio, confirming the F 2 results (χ 2 probability = 0.44 and 0.78 for flowering, and 0.14 and 0.83 for maturity, respectively).Correlations between number of days for flowering and number of days for maturity of F 2 plants and means of their progenies were r = 0.95 (P < 0.01) and r = 0.92 (P < 0.01), for the cross Paraná x Paranagoiana, and r = 0.93 (P < 0.01) and r = 0.89 (P < 0.01), for the cross SS-1 x Paraná, respectively.It was not possible to separate the F 3 families into well-defined groups in the cross SS-1 x Paranagoiana.The small difference in the number of days for flowering and number of days for maturity existing between parents made it impossible to separate the 35 F 3 families studied.The unimodal distribution observed in the F 2 generation indicates that cultivars SS-1 and Paranagoiana are genetically similar (Figures 1C and 2C).However, it was not possible to determine if the alleles of cultivars SS-1 and Paranagoiana are different alleles at the same locus, through the behavior of F 3 lines.Correlation coefficients of number of days for flowering and number of days for maturity between F 2 plants and means of their F 3 lines, in this cross, were r = 0.67 (P < 0.01) and r = 0.75 (P < 0.01), respectively.
The Soybean Genetics Committee has reviewed the information presented and assigned E 6 to the gene determining early flowering and maturity, present in the cultivar Paraná, and e 6 for the gene determining late flowering and maturity in Paranagoiana and SS-1, until the individuality of the alleles of Paranagoiana and SS-1 is confirmed.

ACKNOWLEDGMENTS
Publication supported by FAPESP.
E 6 , A DOMINANT GENE CONDITIONING EARLY FLOWERING AND MATURITY IN SOYBEANS Emídio Rizzo Bonato 1 and Natal Antonio Vello 2 ABSTRACT Inheritance was studied in natural variants of the soybean cultivar Paraná, developed under photoperiodic conditions ranging from 13 h 31 min day light, at sowing, to 14 h 23 min, 59 days afterwards.Results indicated that early flowering and maturity are controlled by a single dominant gene.Natural mutations that originated cultivars Paranagoiana and SS-1 occurred at the same locus of cultivar Paraná.It was not possible to determine if the recessive alleles of these mutant cultivars are different.The designation E 6 was proposed for the alleles determining earliness in cultivar Paraná, and e 6 for the gene determining late flowering and maturity in cultivars Paranagoiana and SS-1, until the individuality of the alleles of Paranagoiana and SS-1 is confirmed.

Figure 1 -Figure 2 -
Figure1-Frequency of plants of parents and of F 2 generations for the number of days to flowering in three soybean crosses.

Table II -
Classification of F 3 soybean families according to the average of F 2 plants, range, average, and phenotypical variance of number of days to maturity in comparison to the parents of crosses Paraná x Paranagoiana, SS-1 x Paraná, and SS-1 x Paranagoiana.
a Progeny tested in the F 3 .b Range of plants of the parents and of F 3 family means.

Table I -
Classification of F 3 soybean families according to the average of F 2 plants, range, average, and phenotypical variance of number of days to flowering in comparison to the parents of crosses Paraná x Paranagoiana, SS-1 x Paraná, and SS-1 x Paranagoiana.Progeny tested in the F 3 .b Range of plants of the parents and of F 3 family means. a