Late summer drought during seed formation often limits yield of soybean [Glycine max (L.) Merr.] grown in the southern U.S. A field study was conducted to determine if earlier planting of early‐maturing varieties could avoid periods of drought stress by having their reproductive development coincide with periods of greater available moisture. Varieties in Maturity Groups (MG) III to VII were planted in mid‐April and in mid‐May near Blossom and Hooks, TX, from 1986 to 1988. There were significant year and location effects on yield. Two MG III varieties planted in April 1986 at Blossom yielded eight times more than the MG V to VII varieties. Negative correlations were found between yield and maturity date in 1986 and 1987. Early drought stress in 1988 reduced yields about 30% for the April‐planted MG III and IV varieties, but yield was again negatively correlated with maturity date. Yields at the Hooks site were up to 45.8 bu/acre higher than those at Blossom, but they were also negatively correlated with maturity date in the April 1986 planting. The seasonal rainfall at Hooks in 1987 was less than half that of 1986 resulting in varietal yields from the early planting being reduced from 8.3 up to 47.1 bu/acre. A negative correlation was still found between maturity date and yield. In 1988, however, late‐season rainfall resulted in a positive correlation between yield and maturity for the April planting. Results from this study show that an early soybean production system using adapted MG III and IV varieties can avoid the effects of late summer drought and result in acceptable yields. Research Question Late summer drought stress often limits yield of soybean grown in the southern USA. A field study was conducted to determine if earlier planting of early‐maturing varieties could avoid periods of drought stress by having reproductive development coincide with times of greater moisture availability. Literature Summary In northeast Texas, as in most of the southern USA, the optimum planting time for MG V to VII varieties is considered to be from mid‐May to early‐June. Under such production systems, flowering, pod‐set, and seed filling occur from late July to early September. This period of reproductive development often coincides with prolonged periods of low rainfall and high temperature. It would be advantageous to shift this period of high water requirement to a time of greater moisture availability, as commonly occurs in June and early‐July. Planting MG V to VII varieties earlier (mid‐April) does not achieve this goal because plants still mature within 7 to 10 d of plants seeded at optimum dates. Moreover, the short‐days of April may induce premature flowering that results in reduced plant height and limited yield potential for traditional determinate plant types. While MG V to VII varieties are primarily determinate, MG III and IV varieties are generally indeterminate. Indeterminate types continue to grow vegetatively after flowering begins; thus, plant heights are reduced less than those of determinate types plan...

Yield tended to increase as RS decreased in years of average rainfall, but the differences were not significant. In the southern USA, determinate soybean grown in row spacingsIn an above-average rainfall year, however, a soybean (RS) of 50 cm or less generally produce higher yields than that grown planting system with 25-cm RS outyielded the 100-cm in RS of 75 to 100 cm. However, the Early Soybean Production System (ESPS) commonly employs indeterminate cultivars in environments RS by 17%. Alessi and Power (1982) reported that, in with limited rainfall. This study was conducted to determine whether 2 yr of a 4-yr study, total water use was greatest and RS affects seed yield in the ESPS. Twenty-one field experiments were average soybean yields were least from a 15-cm RS conducted from 1984 to 1997 at sites in Arkansas, Louisiana, and compared with 45-or 90-cm RS. Their data suggested Texas to determine the effect of RS on seed yield in the ESPS. Row that planting in 15-cm rows enhanced water use prior spacings of 80 and 40 cm were compared in seven tests; of 75, 50, and to flowering. They concluded that, in extreme drought 25 cm in six tests; of 75 and 25 cm in one test; of 100, 50, and 25 cm situations, this enhanced early-season water use left less in four tests; and of 100 and 25 cm in three tests. One to five Maturity

BOWERS, G. R., Jr., and R. M. GOODMAN. 1979. Soybean mosaic virus: Infection of soybean seed parts and seed transmission. Phytopathology 69: 569-572.

Stem Canker caused by Diaporthe phaseolorum (Cooke & Ellis) Sacc. var. caulivora K. L. Athow & R. M. Caldwell (Dpc) has become a serious disease of soybean [Glycine max (L.) Merr.] throughout the southeastern USA. Sources of resistance have been identified and information on the inheritance of resistance is needed for each source. The objective of this work was to study the inheritance of resistance to stem canker in ‘Crockett’ and ‘Dowling’ soybean. Crockett, Dowling, and ‘Tracy‐M’ were crossed with each other and with two susceptible cultivars, Coker 338 and Johnston. Disease reactions of parent and progeny populations were studied in the greenhouse following artificial (toothpick) incoculation with a southern isolate of Dpc. Crosses between either Dowling or Crockett and the two susceptible parents resulted in segregating F2 populations that fit a 3 resistant : 1 susceptible ratio, and F2:3 families that fit a 1 resistant : 2 segregating : 1 susceptible ratio. The cross between Crockett and Dowling resulted in a 15:1 ratio in the F2 and a 7:8:1 ratio in the F3 generation. Crosses between Tracy‐M and Crockett or Dowling resulted in segregation ratios of 63:1 in the F2 and 37:26:1 and F3. These results suggest that Crockett and Dowling each have a major dominant gene, and that these two genes are different from RdC1 and RdC2 found in Tracy‐M. The gene symbols Rdc3 and Rdc4 are proposed to identify genes controlling resistance to stem canker in Crockett and Dowling, respectively.

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Soybean mosaic virus (SMV) is a major disease problem in soybean [Glycine max (L.) Merr.] production in several regions in the world. The disease is controllable with plant resistance. This study was undertaken to elucidate the genetics of SMV resistance in the cultivar Buffalo and in the breeding line HLS so they can be used effectively in breeding programs. Buffalo and HLS were crossed to the SMV‐susceptible cultivar Jupiter and with each other. Portions of the F1, F2, and F2:3 populations from each cross were inoculated with one of seven SMV strains (G1∓G7). Virus inoculations were done in the field or greenhouse using an air‐brush technique. Chi‐square analysis of the segregation ratios of populations from the Buffalo × Jupiter cross show that Buffalo's resistance to SMV strains Gl to G7 is under monogenie control, and exhibited dominance under the conditions of this study. Results of the HLS × Jupiter cross show that resistance in HLS to SMV strains G5, G6, and G7 is also conditioned by a single dominant gene. When inoculated with SMV strain G5, G6, or G7, populations of F2 plants from the cross Buffalo × HLS segregated in the ratio of 15 resistant to 1 susceptible. This result, supported by the F2:3 segregation data, suggests that the SMV resistance genes in Buffalo and HLS are located at different loci.

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