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Growing demand for soybean [Glycine max (L.) Merr.] creates pressure to expand soybean production onto marginal lands and grow soybean continuously. Experiments comparing continuous soybean with soybean–corn (Zea mays L.) rotation, cereal rye [Secale cereale (L.)] cover crop with no cover crop, and flue‐gas desulfurization (FGD) gypsum surface‐applied at 0, 1.1, and 2.2 Mg ha−1 were conducted at Shorter, AL, Farmland, IN, Hoytville, OH, and Piketon, OH, for 5 yr. The objective was to evaluate soybean yield response to these practices across a range of soil types and climatic conditions. Response to continuous soybean and cover crop varied by site (soil drainage class) with no interaction effects. Continuous soybean reduced yield only on well‐ and moderately well‐drained soil types. Cover crop reduced yield on the very poorly drained soil type and increased yield on the well‐drained soil type. Crop production practices that promote soil health and sustainability may not provide yield improvement.

Soybean (Glycine max L. Merr.) cultivars from the U.S. are generally intolerant to flooding stress. Soybean germplasm and cultivars originating from other countries and grown in rotations with paddy rice potentially could have better flooding tolerance. Screen-house and field tests were conducted to determine variations in flooding tolerance among 21 soybean varieties from Southeast Asia. Flooding for two weeks at the R2 growth stage reduced grain yield under field conditions between 36% and 100% (all plants dead). However, plants that survived were, on the average, 13% taller than control plants. Tolerance to R2 flooding was associated with higher number of pods per plant and 100-grain weight. Growth response to flooding stress, as determined by plant height, was correlated with grain yield in all three environments. While there was no correlation in yield between field and screen-house tests, the flood tolerance ranking of the field test was correlated with the ranking of one screen-house test. Screen-house tests could distinguish tolerant from susceptible varieties based on plant survival and grain yield. Three varieties - VND2, Nam Vang and ATF15-1 - showed the best flooding tolerant responses under field and screen-house conditions. These lines provide new germplasm resources for the genetic improvement of flooding tolerance in soybean.

Plants have evolved adaptation mechanisms to sense oxygen deficiency in their environments and make coordinated physiological and structural adjustments to enhance their hypoxic tolerance. To gain insight into how plants respond to low-oxygen stress, gene expression profiling using whole-genome DNA amplicon microarrays was carried out at seven time points over 24 h, in wild-type and transgenic PSAG12:ipt Arabidopsis (Arabidopsis thaliana) plants under normoxic and hypoxic conditions. Transcript levels of genes involved in glycolysis and fermentation pathways, ethylene synthesis and perception, calcium signaling, nitrogen utilization, trehalose metabolism, and alkaloid synthesis were significantly altered in response to oxygen limitation. Analysis based on gene ontology assignments suggested a significant down-regulation of genes whose functions are associated with cell walls, nucleosome structures, water channels, and ion transporters and a significant up-regulation of genes involved in transcriptional regulation, protein kinase activity, and auxin responses under conditions of oxygen shortage. Promoter analysis on a cluster of up-regulated genes revealed a significant overrepresentation of the AtMYB2-binding motif (GT motif), a sugar response element-like motif, and a G-box-related sequence, and also identified several putative anaerobic response elements. Finally, quantitative real-time polymerase chain reactions using 29 selected genes independently verified the microarray results. This study represents one of the most comprehensive analyses conducted to date investigating hypoxia-responsive transcriptional networks in plants.

Most of the phosphorus (P) in maize (Zea mays L.) kernels is in the form of phytic acid. A low phytic acid (lpa) maize mutant, lpa1-1, displays levels reduced by 66%. A goal of genetic breeding is development of low phytic acid feedstocks to improve P nutrition of nonruminant animals and reduce the adverse environmental impacts of excess P in manure. The genetic basis of the lpa1-1 mutation is not known, but previous genetic mapping has shown both the mutant phenotype and the Ins (3) P(1) synthase (MIPS) gene, which encodes the first enzyme, myo-inositol phosphate synthase, in the phytic acid biosynthetic pathway, map to the same chromosomal region in maize. Research was conducted to determine the expression of the MIPS gene in lpa1-1 and wild-type kernels with similar genetic backgrounds and to ascertain if variation in the MIPS coding sequence could be inferred to be the basis of the mutation. MIPS enzyme activity determined by TLC was reduced 2-3-fold in mutant kernels. RT-PCR-based experiments using primers specific for the 1S-MIPS sequence indicated gene expression was reduced 50-60% in the mutant. Sequence analysis of the MIPS genomic sequence revealed 10 exons and 9 introns that are identical in both mutant and wild-type developing kernels. These findings support an association between reduced MIPS gene activity and low phytic acid content, but additional research should examine the promoter, the 5'UTR, or transcriptional controlling elements of the MIPS gene to ascertain the possible presence of a genetic lesion in those regions.

Sequence-Characterized Amplified Region (SCAR) appears as a useful technique for genetic purity testing and variety discrimination, applicable to species in which some other techniques have failed. In particular, this technique is very attractive with species in which RAPD results were not consistent. The RAPD polymorphic bands were cloned, sequenced and from the sequence information, primers pairs for normal PCR were developed. Since the probability of obtaining successful SCAR primers from RAPD polymorphic bands was about 50%, a larger number of RAPD polymorphic bands are needed to develop sufficient SCAR primers for varietal discrimination in vinca. In addition, the efficiency of the SCAR technique is strongly affected by the quality of DNA extracted from seeds. The SCAR banding patterns obtained from vinca seed were consistent and repeatable making the results reliable for genetic purity testing and variety discrimination. The SCAR technique is simple, fast, relatively inexpensive and allows the use of DNA extracted from dry seeds, which is very important in a seed-quality evaluating program

Soil waterlogging is a major environmental stress that suppresses soybean [Glycine max (L.) Merr.] growth and yield. Our objective was to identify quantitative trait loci (QTL) associated with the tolerance of soybean to soil waterlogging. We subjected 208 lines of two recombinant inbred (RI) populations, Archer' × 'Minsoy' and Archer' × 'Noir I', to 2 wk of waterlogging when the plants were at the early flowering stage. The control plants were not flooded. The experiment was conducted in three environments: Columbus, OH, in 1997 and 1998 and Wooster, OH, in 1998. We identified a single QTL, linked to marker Sat―064, from the Archer parent which was associated with improved plant growth (from 11-18%) and grain yields (from 47-180%) in waterlogged environments. This highly significant QTL (P = 0.02-0.000001) was identified in both RI populations and at both Columbus 1997 and 1998 environments, but not at the Wooster 1998 environment. The differences in soil type and flooding treatment (stagnant versus moving water) could have contributed to the lack of QTL identification at the Wooster 1998 environment. The Sat―064 QTL was uniquely associated with waterlogging tolerance and was not associated with maturity, normal plant height or grain yields. The Sat―064 marker maps close to the Rps4 gene for Phytophthora (Phytophthora sojae MJ. Kaufmann & J.W. Gerdemann) resistance; however, since Archer does not contain the Rps4 resistance allele, it is probably not a disease tolerance QTL. Near isogenic lines with and without the Sat―064 marker have been developed and are being field tested under waterlogging conditions to confirm the association of the QTL with the tolerance of soybean to waterlogging stress.

Flooding is a major problem that reduces soybean [Glycine max (L.) Merr.] growth and grain yield in many areas of the USA and the world. Our objective was to identify the plant and soil characteristics associated with different flooding durations in six fields in central Ohio. The soybean plants were at the V2 and V3 stages when rainfall-induced flooding occurred. The outer perimeters of the flooded areas were mapped, using GPS (global positioning system) technology, several times during the flooding event to delineate the change of the flooded area over time. Two 9-m wide transects across the flooded area within each field were divided into plots of 9 m by 9 m according to flooding duration: no flooding, 1 to 3 d, 4 to 6 d, and 6 to 8 d. Soil and plant nutrient levels, grain yield data and grain protein and oil content were determined for each plot. The soil cation-exchange capacity (CEC), pH, P, Ca, Mn, and Zn concentrations had significant positive correlation with flooding duration. There was a significant negative correlation of flooding duration with the population, height, number of pods, and yield of soybean. There was no significant correlation of flooding duration with seed weight, oil, or protein content of the seeds. Leaf tissue Ca, Mg, B, Fe, Cu, and Al concentrations had a significant positive correlation with flooding duration, whereas leaf tissue N concentration had a significant negative correlation with flooding duration.

Estimates of proportions of parental contribution to germplasm populations are useful to breeders. The objective of this research was to assess the ability of amplified fragment-length polymorphism (AFLP) markers to characterize the contributions of the original parents to later cycles of a soybean [Glycine max (L.) Merr.] population that had undergone recurrent selection. Use of four primer pairs yielded a total of 47 polymorphic bands. Estimates of parental contribution were consistent between primer pairs and between cycles and conformed to those expected based on pedigrees. Standard errors of estimates were 3 to 5%, indicating satisfactory precision. The AFLP markers should provide relatively inexpensive, precise estimates of parental contribution. This marker system may also be useful in tracking genetic changes in populations.

The flooding tolerance of U.S. soybean [Glycine max (L.) Merr.] cultivars under field conditions has not been reported. In this study, 84 soybean cultivars of maturity groups II, III, and IV were grown at two locations, London and Lakeview, in Ohio. The cultivars differed in their resistance and tolerance to Phytophthora sojae M.J. Kaufmann & J. W. Gerdemann as determined in separate field and laboratory studies. While the production practices and historic yield potential at the two locations were similar, the nearly flat, slowly permeable Milford silty clay soil at Lakeview was saturated during most of July 1992 because of excessive rainfall (17 cm more than normal). The average yield of the 84 soybean cultivars at the flooded location (Lakeview) was 25% lower than at the non-flooded location (London). Flooding tolerance can be defined as high yield under flooding stress. When the 84 soybean cultivars were ranked in their flooding tolerance according to this definition, many cultivars were found to exhibit both flood tolerance at Lakeview and high yield at London. Flooding tolerance was independent from Phytophthora tolerance, Phytophthora resistance, and plant relative maturity. This study documented that differences in flooding tolerance exist among U.S. soybean cultivars. OARDC Journal Article no. 116-93.

The postanoxic injury, also known as reperfusion injury, is associated with the returning of anoxic tissues to normal atmosphere. Using tetrazolium chloride staining, ATP content, and seedling growth rate as indicators, we found that postanoxic injuries in soybean (Glycine max) seedlings were more severe after 1 and 2 hours of anoxia than after longer anoxic durations (3 to 5 hours). Anaerobic incubation of root tips in the presence of 100 mm ascorbate, an antioxidant and free radical-scavenging compound, alleviated the postanoxic injury associated with the short durations of anoxia. Extracts from soybean seedling roots returned to air from 1 hour of anoxia had an elevated capacity to produce superoxide radicals over extracts from postanoxic roots stressed for 3 or 5 hours. Activity of superoxide dismutase in soybean roots returned to air from 1 and 2 hours of anoxia was 30 to 50% lower than activities in roots returned to air from 5 hours of anoxia. Superoxide dismutase-specific transcripts were also lower in postanoxic roots stressed for 1 hour than in roots stressed for longer anoxic durations. The evidence suggested that the postanoxic injury of soybean roots after a short anoxic stress was associated with an increased superoxide radicals production capacity coupled with a reduced superoxide dismutase activity. Periods of anoxia of at least 3 hours were necessary for soybean seedlings to develop the ability to cope with postanoxic stress.

The Adh1 gene coding for alcohol dehydrogenase (ADH) enzyme is one of the most widely studied genes in plants. Some controversy exists, howevern concerning the induction of ADH activity in soybean [Glycine max (L.) Merr.] by flooding stress. This study showed that the induction of ADH in 5- to 21-d-old soybean seedlings by flooding was organ-specific and changed with seedling age

Soybean (Glycine max) alcohol dehydrogenase (ADH) cDNAs were amplified in vitro from total RNA by the polymerase chain reaction (PCR). The amplification strategy involved first strand cDNA synthesis from anaerobic cotyledon total RNA using an 18-thymidine primer. The second strand cDNA primer was a conserved sequence near the 5′ end of known plant ADH transcripts. The PCR products were ligated into a plasmid vector and unique clones were isolated on the basis of size and restriction pattern. Sequence analysis revealed three distinct classes of soybean ADH cDNAs, all of which showed high homology to Adh genes from maize and peas. RNA blot hybridization analyses showed differential expression patterns for these genes. One gene, expressed constitutively in all seedling organs, was inducible by anaerobiosis, one gene was expressed only in anaerobic organs, and the third gene was expressed predominantly in anaerobic roots.

Flooding is a frequently occurring environmental stress that can severely affect plant growth. This study shows that treatment of corn (Zea mays L.) seedlings with abscisic acid (ABA) increases their tolerance to anoxia 10-fold over untreated seedlings and twofold over seedlings treated with water. Corn seedlings stressed anoxically for 1 day showed only 8% survival when planted in vermiculite. Pretreatment of root tips with 100 micromolar ABA or water for 24 hours before the 1 day anoxic stress increased the anoxic survivability of seedlings to 87% and 47%, respectively. Cycloheximide (5 milligrams per liter), added together with ABA, reduced the seedling survival rate, indicating that the induction of anoxic tolerance in corn by ABA was partly a result of the synthesis of new proteins. ABA treatment induced a threefold increase in alcohol dehydrogenase enzyme activity in corn roots. However, after 24 h of anoxia, alcohol dehydrogenase enzyme activity between the ABA-pretreated and non-pretreated corn roots was not significantly different. The results indicated that ABA played an important role in inducing anoxic tolerance in corn and that the induced tolerance was probably mediated by an increase in alcohol dehydrogenase enzyme activity before the anoxic stress.

Abscisic acid (ABA) applications can improve plant resistance to stresses such as cold, drought, and salinity. Treatment of corn (Zea mays L.) with ABA was previously shown to increase flooding survival 10-fold. The long-term effect of ABA treatment and flooding stress on growth and productivity have not been documented. In this study, ABA-treated corn seedlings that survived a flooding stress in the laboratory were transplanted to the field and their growth and seed yield compared with those of nonflooded plants (.)