Cultivars Of Maturity Groups Research Articles

Resistance in Soybeans to the Southern Green Stink Bug1

The southern green stink bug [Nezara viridula (L.)] is a pest soybean [Glycine max (L.) Merr.] in many areas of the Southern U.S., particularly in Louisiana and other Gulf Coast states, as well as in other countries where soybeans are grown. To identify resistance to the southern green stink bug, 894 plant introductions and 26 cultivars of Maturity Groups V through VIII were evaluated in replicated single row field plots during 1975 to 1979 at Baton Rouge, LA. Damage ratings were made by classifying 100 seeds selected at random from each sample into four categories (none, light, medium, and severe) on the basis of visual damage.Stink bug damage was associated with plant maturity, with earlier maturing genotypes generally having less damage than later maturing genotypes. Significant differences in stink bug damage were detected among cultivars within Maturity Group VI. There were no differences in damage among cultlvars within Groups V, VII, or VIII. However, all cultivars had in excess of 60% damage and were highly susceptible to stink bug feeding.Highly significant differences in damage were obtained among plant introductions. Of the 894 strains evaluated, 67 had significantly less damage than the most resistant cultivar of similar maturity, and appeared to have resistance. These strains were from fairly diverse geographical locations and may represent different sources of resistance. There were no differences in damage among the more resistant strains within Maturity Groups V, VII, or VIII. However, the Group VI strain PI 171444 had significantly less damage than the other more resistant Group VI strains. This strain had the lowest stink bug damage rating in the test during all years, and appeared to have a high level of southern green stink bug resistance.

Response to Recurrent Selection for Yield in Soybeans 1

The objectives of our research were to evaluate response to recurrent selection for seed yield in a soybean [Glycine max (L.) Merrill] population and to assess the effect of selection on other agronomic characters. Forty high-yielding lines and cultivars of Maturity Groups 0 to IV were intermated three generations without selection to form the population AP6. The parents of the cycle 1 population were identified by testing 300 F3-derived lines of the cycle 0 population, subdividing the 300 lines into three sets of 100 by maturity, and selecting the 10 early, midseason, and late lines with the highest yields. The 30 parents were recombined in a diallel without reciprocals, and 300 F4-derived lines of the cycle 1 population were tested for yield. The 300 lines were subdivided into three sets of 100 by maturity, and the 10 lines with the highest yields from the three maturity classes were chosen as the parents of cycle 2. The 10 parents of each maturity were mated in separate diallels, 100 F4-derived lines for each maturity were tested for yield, and the 10 lines with the highest yields of each maturity were chosen as parents of cycle 3. Each cycle of selection required 2 years. Response to selection was evaluated by testing the individual parents of cycles 0 to 3 and a composite of the parents of cycles 1 to 3 as three maturity sets in six Iowa environments during 1979 and 1980. The response to selection for yield was similar when evaluated as the mean performance of individual parents or as a composite of the parents. There was a significant linear increase in yield of 120 ± 10 kg/ha per cycle for the mean of early parents and 24 ±9 kg/ha per cycle for the late, but no significant change in yield for the mean of midseason (- 14± kg/ha) parents. Yield of the best parent in cycle 3 was not significantly better than the yield of the best parent of cycle 0 for any maturity set. There was no consistent change in maturity, lodging, height, seed weight and protein and oil percentage caused by the selection for yield.

Moisture Migration into Soybean Pods1

An evaluation of moisture absorption by soybean [Glycine max (L.) Merr.] pods was conducted in 1978 and 1979. Forty‐six cultivars representing Maturity Groups II through VI were grown to harvest maturity in the field. Representative plants from each cultivar were taken to the laboratory and intact pods were removed from each plant. In each year, two sets of 20 pods from each cultivar were submerged in water for 0, 1, 6, and 24 hours to allow moisture uptake by the pod and seed.Pods and seeds from cultivars in Maturity Groups II through IV absorbed significantly more moisture than those from Maturity Groups V and VI. Pods of ‘Williams’ and ‘Celest’ absorbed the least amount of moisture in Maturity Groups III and V, with both having absorbed approximately 78.0 g H2O/100 g dry wt at 24 hours. Water uptake in these two cultivars were significantly different from the cultivars that absorbed the most water within their respective maturity groups. Seed of ‘Perry’ and ‘Ware’ absorbed the least moisture of the 16 cultivars in Maturity Group IV.

Epidemiology of Phomopsis Seed Decay of Soybean in Illinois

Phomopsis spp. were recognized by a SHORTT, B. J., A. P. GRYBAUSKAS, F.D. TENNE, and J. B. SINCLAIR. 1981. Epidemiology characteristic thick, white coating of of Phomopsis seed decay of soybean in Illinois. Plant Disease 65:62-64. mycelium with or without typical Phomopsis pycnidia. Phomopsis is by far In a 3-yr study of seed decay of soybean (Glycine max) caused by Phomopsis spp. in Illinois, disease the predominant cause of soybean seed incidence was highest in 1977, lowest in 1976, and intermediate in 1975. A low positive correlation decay in Illinois and can be distinguished was found between temperature and disease incidence, but no consistent continuum of disease from from other seed inhabitants by the color, north to south within the state was apparent. The highest incidence of Phomopsis seed decay texture, and growth habits of the mycelial occurred along major waterways in the wet years of 1975 and 1977. A high positive correlation was mat. Other pathogens of soybean seeds found between disease incidence and rainfall during pod fill, indicating that moisture, rather than were infrequently observed. Therefore, temperature or geographic area, is the dominant environmental factor in disease development. we believe that the experimental erro Maturity dates of cultivars interacted with changing weather conditions to affect disease incidence. we b asi ng our t ifications error In our studies, cultivars in maturity group II had the highest level of Phomopsis seed decay. from basing our identifications on gross Cultivars used in seed production in Illinois should be grown at latitudes where they will mature late fungal morphology is very low. in the season and escape conditions conducive to high incidence of seed decay. The data were collected from 2,708, 2,713, and 2,699 seedlots harvested in 1975, 1976, and 1977, respectively, and Phomopsis seed decay of soybean seed decay of certified soybean seeds were analyzed with the Statistical (Glycine max (L.) Merr.) is part of a grown throughout Illinois in 1975-1977. Analysis System prepackaged computer disease complex caused by species of

Response of Soybean Cultivars to Planting Patterns1

AbstractSince soybean [Glycine max (L) Merr.] acreage continues to increase in the higher latitudes of the world the objective was to obtain agronomic information on the effect of inter and intra‐row spacings on several of the most widely grown, early cultivars in America. Ten soybean cultivars differing in maturity (Group 0 through II) and growth characteristies were grown in two row spacings (27‐cm and 76‐cm) and varying populations (132,000 to 741,000 plants/ha) for 3 years in field trials on Typic Arguidolls fine silty; mixed mesic soil near Madison, Wis.Planting soybeans in 27‐cm rows vs. more conventional 76‐cm rows showed an average seed yield increase of 21% over all years, populations, and cultivars. All cultivars produced higher seed yields in narrow row spacings. The three early cultivars (Group O Maturity) generally exhibited a greater yield response (+27%) to narrow row spacings than did cultivars in Maturity Groups I and II (+19%). However, the later maturing cultivars generally produced the highest yields over all row spacings, plant populations and years. Varying the intra‐row plant spacing did not significantly affect seed yields. Increasing plant populations decreased the number of branches per plant and increased lodging, seed weight, and LAI. While the LAI increased as plant population increased in both the narrow and wide rows, no correlation existed with grain yield. Increasing the plant population in each row spacing increased the height of the lower pod by a range of 40 to 50%.The availability of new varieties with improved lodging resistance and herbicides with greater selectivity may lead to an accelerated acceptance of narrow row soybean production systems to capitalize on the increased yield potential in the northern growing regions.

Comparison of Past and Recently Developed Soybean Cultivars in Maturity Groups VI, VII, and VIII1

In the southeastern U.S., soybean [Glycine max (L.) Merr.] seed yields have increased due to improved cultivars, cultural practices, and general management. To determine the contribution of improved genotypes to this increase, 18 cultivars in maturity groups VI, VII, and VIII ranging in introduction or release date from 1914 to 1973 were evaluated in a common environment for 3 years. Other plant traits were evaluated to determine if differences existed among cultivars and if these differences were associated with year of release and seed yield. The regression of seed yield on year of release indicated significant genetic improvement in seed yield had occurred. Averagedo ver all maturity groups for the period 1942 to 1973, this increase was 0.7%/year. For cultivars in maturity group VIII, pods/m, plant height, and number of nodes were related to year of release. The differences in plant height and nodes/plant for cultivars in maturity group VIII were primarily due to the indeterminate growth habit of ‘Yelnanda’ and ‘Improved Pelican.’ The other cultivars in this experiment have the determinate growth habit. The differences for traits other than yield in cultivars within maturity groups VI and VII were not associated with year of release. The yield increase of recently developed cultivars was not consistently associated with any of the traits measured.

Effect of Planting Date on Natural Selection in Soybean Populations1

Early‐maturing segregates are frequently eliminated in soybean (Glycine max (L.) Merr.) bulk populations. Six simulated bulks were made of five cultivars in maturity groups I through V, the two cultivars in each bulk differed by at least two maturity groups. These bulks were planted at several dates in 4 years to determine whether late planting would increase the relative reproduction of the early cultivars in the bulks. Their relative reproductivity increased twice, decreased once, and did not change once. The early cultivars in all bulks were at a reproductive disadvantage compared to the relationship in pure stands. The reproductive disadvantage tended to increase with differences in the time of maturity in the simulated bulks, although plant size probably was more important than maturity per se. Even though the early cultivars in the bulks did not consistently gain in reproductive advantage with late planting, late planting should help maintain them in bulk populations because of improved seed quality.

Response of Soybeans to End‐Trimming at Various Growth Stages1

Two soybean (Glycine max (L.) Merrill) cultivars in each of maturity groups I to IV were end‐trimmed at seven growth stages, from the first trifoliolate stage to maturity. Seed yield and seed size were recorded on two .3‐m sections at the ends of plots and on a 3‐m section in the center of plots. Data indicated that significant border effects in maturity groups II to IV, grown at Lafayette, Ind., extended more than .3‐m from the ends of plots. Border effects could be adequately controlled by trimming .6 m from each end of the plots when the top pods on plants were fully extended with seeds approaching full size for cultivars in groups I to III. Trimming would have to be delayed until leaves on plants were 30 to 50% yellow with a few falling for group IV varieties or strains. Plot yields could be adjusted to those of 4.9‐m rows trimmed at maturity by end trimming to 4.9 m at or before the first trifoliolate stage and multiplying plot yields by .874, .840, .796, and .755 for cultivars in maturity groups I to IV, respectively. Size of seed on plants at the ends of rows was increased only when end trimming was done at full bloom or as soon as flowering ceased.