Nodule distribution on the roots of soybean and a supernodulating mutant in sand-vermiculite

The distribution of nodules of soybean (Glycine max (L.) Merr.) cultivar Bragg and the supernodulating mutant derivative nts382 was examined on the primary root relative to the first emerging lateral root, and on laterals relative to the base of the roots of plants grown in sand-vermiculite. Mutant nts382 nodulates profusely even in the presence of nitrate and appears defective in a systemic autoregulatory response that regulates nodule number in soybean. Nodules were clustered on primary roots about the first 4 cm down from the first emerging lateral root in both genotypes. Nodulation profiles showed reduced nodulation in younger and older regions of the primary root. Similarly, nodules appeared clustered close to the base of the lateral roots. Decreasing inoculum dose shifted nodule emergence to younger regions of the primary root and to lateral roots emerging in younger portions of the primary root. Our results indicate that the supernodulating mutant is able to regulate nodule number in both primary and lateral roots in the particulate matrix.     

Comparison of somatic embryogenesis and embryo conversion in commercial soybean cultivars

Six commercially important soybean cultivars and one control cultivar were compared for differences in induction-efficiency of somatic embryogenesis, primary embryo yield, and embryo conversion. Cotyledons from immature seeds of similar developmental stage for all soybean cultivars were used for embryo induction. The experiments utilized a Latin square design to exclude the effect of differential lighting and position due to plate location in the growth chamber on the embryogenesis process. Results indicated that the efficiency of embryo induction and yield of primary somatic embryos were genotype-dependent. In contrast, no dependence on genotype was observed for the conversion of embryos to form roots and shoots. The percentage of cotyledons that gave a positive embryogenic response ranged from 26 to 89% for the soybean cultivars tested. The average number of primary globular-stage embryos per responding cotyledon after one month on induction medium ranged from 6 to 13 among the seven cultivars. Conversion frequencies for all genotypes ranged from 27 to 45%.     

Enhanced nodulation of soybean by Bradyrhizobium in the presence ofPseudomonas fluorescens

Experiments were undertaken to determine the effect ofPseudomonas fluorescens on nodulation of soybean by two strains ofBradyrhizobium japonicum, USDA I-110 and 61A76.Pseudomonas fluorescens can enhance the nodulation ability ofB. japonicum. Preincubation ofB. japonicum withP. fluorescens before inoculation further increased the level of nodulation.     

The influence of soybean planting density on dinitrogen fixation and yield

We investigated the effect of planting density on soybean (Glycine max (L.) Merr.) yield in glasshouse and field experiments. Because net canopy photosynthesis increases with increasing plant density, we hypothesized that increasing planting density would result in increasing rates of dinitrogen fixation in soybeans and higher yields per unit land area.In glasshouse studies, Wayne variety soybeans were planted in 10-cm diameter pots, 1 plant pot^-1 in matrices of 10-, 15-, 20-, 25-, or 30-cm equidistant intervals. Bradyrhizobium japonicum inoculum was added to half of the plants in each treatment. Replicate measurements of total stem height, internode lengths, leaf mass, stem mass, root mass, nodule number, nodule mass, and nitrogenase activity were obtained at 3, 6, and 9 weeks post-emergence. Fruits were harvested and counted at week 14. As planting density increased there were (1) altered morphology and growth rates, (2) increased apparent specific nodule activity (SNA), (3) decreased nodule number and mass, and (4) nearly constant fruit and seed production/plant. Expressed on a unit area basis, nitrogen influx and yield increased geometrically as planting density increased, with maximum values observed for 10-cm plantings.Field studies of Wayne, Stein, Williams, and Gold Harvest soybean varieties were made in 1985. Plots were established containing 100 plants spaced at 10-, 20-, and 30-cm distances. Measurements made during the growing season and at harvest established the same relative trends identified from the glasshouse studies. Increasing plant densities resulted in higher yields per unit land. Varietal differences were almost significant.     

Membrane lipid peroxidation, nitrogen fixation and leghemoglobin content in soybean root nodules

Membrane lipids in soybean nodules may undergo oxidative degradation resulting in the loss of membrane structural integrity and physiological activities. One of the final products of lipid peroxidation is malondialdehyde (MDA), which can react with thiobarbituric acid (TBA) in vitro to form a chromogenic adduct, a Schiff base product that can be measured spectrophotometrically. MDA formation was quantified in the nodules as well as in the adjacent root tissue. Lipid peroxidation was initially high in soybean nodules induced by Bradyrhizobium japonicum, but sharply declined following an increase in both leghemoglobin content and nitrogen fixation rate. Lipid peroxidation was 2 to 4 times higher in the nodules than in their corresponding adjoining root tissue. Malondialdehyde levels in ineffective nodules were 1.5 times higher than those in effective nodules. MDA formation was also shown to occur in the ‘leghemoglobin-free’ cytosolic fraction, the ‘leghemoglobin’ fraction, and the nodule tissue pellet. Antioxidants, such as reduced ascorbic acid, glutathione, and 8-hydroxyquinoline, caused a partial suppression of lipid peroxidation, whereas ferrous sulfate, hydrogen peroxide, iron EDTA, disodium-EDTA, and β-carotene induced MDA formation. In contrast, quenchers of oxygen free radicals such as HEPES, MES, MOPS, PIPES, phenylalanine, Tiron, thiourea, sodium azide, and sodium cyanide (uncouplers of oxidative phosphorylation) caused somewhere between a 12 to 70 percnt; reduction in MDA production. TBA-reactive products were formed despite the incorporation of superoxide dismutase, proxidase, and catalase into the reaction mixture.     

Effect of soil salinity level and zinc application on growth,yield, and nutrient composition of rice

Summary Physiological and symbiotic characteristics were identified in fast-growing (FG)Rhizobium japonicum. Carbon nutritional patterns linked these rhizobia to other FG rhizobia. They were able to use hexoses, pentoses, disaccharides, trioses, and organic acids for growth, but they were unable to use dulcitol or citrate. These rhizobia produced acid with all carbon sources except intermediates of the Krebs cycle. FGR. japonicum showed no vitamin requirements and were tolerant to 1% NaCl but not to 2%. They nodulated cowpea, pigeon pea, and mung bean but not peanut. Effective, nitrogen-fixing symbioses were observed only with cowpea and pigeon pea. In addition, FGR. japonicum formed effective symbioses with Asian-type soybeans. We concluded that although the physiological characteristics of FGR. japonicum were similar to other FG rhizobia, their symbiotic properties were similar to slow-growing rhizobia of the cowpea miscellany.     

Effect of plant genotype and nitrogen fertilizer on symbiotic nitrogen fixation by soybean cultivars

Summary Isotopic as well as non-isotopic methods were used to assess symbiotic nitrogen fixation within eight soybean [Glycine max (L.) Merr.] cultivars grown at 20 and 100 kg N/ha levels of nitrogen fertilizer under field conditions.The¹⁵N methodology revealed large differences between soybean cultivars in their abilities to support nitrogen fixation. In almost all cases, the application of 100 kg N/ha resulted in lower N₂ fixed in soybean than at 20 kg N/ha in the first year of the study. However, N₂ fixed in one cultivar, Dunadja, was not significantly affected by the higher rate of N fertilizer application. These results were confirmed by measurements of acetylene reduction activity, nodule dry weight and N₂ fixed as measured by the difference method. Further proof of differences in N₂ fixed within soybean cultivars and the ability of Dunadja to fix similar amounts of N₂ at 20 and 100 kg N/ha was obtained during a second year experiment. Dunadja yield was affected by N fertilizer and produced larger yield at 100 kg N/ha than at 20 kg N/ha. This type of cultivar could be particularly useful in situations where soil N levels are high or where there is need to apply high amounts of N fertilizer.The present study reveals the great variability between legume germplasms in the ability to fix N₂ at different inorganic N levels, and also the potential that exists in breeding for nitrogen fixation associative traits. The¹⁵N methodology offers a unique tool to evaluate germplasms directly in the field for their N₂ fixation abilities at different N fertilizer levels.     

N2 fixation in Thai soybeans: Effect of tillage and inoculation on15N-determined N2 fixation in recommended cultivars and advanced breeding lines

The practice of seeding soybeans following paddy rice in Thailand has encountered difficulties in seedling germination, nodulation and crop establishment. This research project evaluated the choice of a non-fixing control to quantify N₂ fixation by¹⁵N isotope dilution, and the effect of tillage regime, soybean cultivar, strain ofBradyrhizobium japonicum and P fertilization on yield and N₂ fixation after paddy rice in northern and central Thailand.Japanese non-nodulating lines Tol-0 and A62-2 were the most appropriatecontrol plants for¹⁵N isotope dilution for Thai soybeans in these soils which contained indigenous rhizobia. Cereals such as maize, sorghum and barley were also appropriate controls at some sites. The choice of the appropriate non-fixing control plant for the¹⁵N isotope dilution technique remains a dilemma and no alternative exists other than to use several possible controls with each experiment. Acetylene reduction assay (ARA) proved of little value for screening varieties on their N₂ fixing capacity.The recommended Thai soybean cultivars (SJ1, 2, 4, 5) and an advanced line 16–4 differed little in their ability to support N₂ fixation or yield, possibly due to similar breeding ancestry. The ten AVRDC (ASET) lines showed considerable genotypic control in their ability to utilize their three available N sources (soil, fertilizer, atmosphere) and to translate them into yields. None of these lines were consistently superior to Thai cultivars SJ4 or SJ5 although ASET lines 129, 209 and 217 showed considerable promise.Neither recommended Thai or ASET cultivars were affected by tillage regime. Zero tillage resulted in superior N₂ fixation and yield at two sites but conventional tillage was superior at another site. Soybean cultivars grown in Thailand were well adapted to zero tillage. Levels of N₂ fixation were similar to world figures, averaging more than 100 kg N ha^–1 and supplying over 50% of the plant's N yield. However, seed yields seldom exceeded 2 t ha^–1, well below yields for temperately-grown soybeans. It is not clear why Thai soybeans support N₂ fixation, but do not translate this into higher seed yields.     

Oxidation of the enzymes involved in nitrogen assimilation plays an important role in the cadmium-induced toxicity in soybean plants

Cadmium causes oxidative damage and hence affects nitrogen assimilation. In the present work we tested the relationship between the inactivation of the enzymes involved in nitrogen assimilation pathway (glutamine synthetase (GS)/glutamate synthase (GOGAT)) and the protein oxidation in nodules of soybean (Glycine max L.) plants under Cd²⁺ stress. Therefore, the effect of Cd²⁺ and reduced gluthatione (GSH) on GS and GOGAT activities, and protein abundance and oxidation were analyzed. Under the metal treatment, amino acids oxidative modification occurred, evidenced by the accumulation of carbonylated proteins, especially those of high molecular weight. When Cd²⁺ was present in the nutrient solution, although a decrease in GS and GOGAT activities was observed (17 and 52%, respectively, compared to controls), the protein abundance of both enzymes remained similar to control nodules. When GSH was added together with Cd²⁺ in the nutrient medium, it protected the nodule against Cd²⁺ induced oxidative damage, maintaining GS and GOGAT activities close to control values. These results allow us to conclude that the inactivation of the nitrogen assimilation pathway by Cd²⁺ in soybean nodules is due to an increment in GS and GOGAT oxidation that can be prevented by the soluble antioxidant GSH. Section Editor: H. Schat     

Nod Bj-V (C18:1, MeFuc) production by Bradyrhizobium japonicum (USDA110, 532C) at suboptimal growth temperatures

Nod factors (Lipo-chitooligosaccharides, or LCOs) act as bacteria-to-plant signal molecules that modulate early events of the Bradyrhizobium-soybean symbiosis. It is known that low root zone temperature inhibits the early stages of this symbiosis; however, the effect of low soil temperature on bacteria-to-plant signaling is largely uninvestigated. We evaluated the effect of low growth temperatures on the production kinetics of Nod factor (LCO) by B. japonicum. Two strains of B. japonicum, 532C and USDA110, were tested for ability to synthesize Nod Bj-V (C(18:1), MeFuc) at three growth temperatures (15, 17 and 28 degrees C). The greatest amounts of the major Nod factor, Nod Bj-V (C(18:1), MeFuc), were produced at 28 degrees C for both strains. At 17 and 15 degrees C, the Nod factor production efficiency, per cell, of B. japonicum 532C and USDA110 was markedly decreased with the lowest Nod factor concentration per cell occurring at 15 degrees C. Strain 532C was more efficient at Nod factor production per cell than strain USDA 110 at all growth temperatures. The biological activity of the extracted Nod factor was unaffected by culture temperature. This study constitutes the first demonstration of reduced Nod factor production efficiency (per cell production) under reduced temperatures, suggesting another way that lower temperatures inhibit establishment of the soybean N(2) fixing symbiosis.     

Inoculation of soybean (Glycine max. (L.) Merr.) with genistein-preincubated Bradyrhizobium japonicum or genistein directly applied into soil increases soybean protein and dry matter yield under short season conditions

In short-season soybean production areas, low soil temperature is the major factor limiting plant growth and yield. The decreases in soybean yield at low temperatures are mainly due to nitrogen limitation. Genistein, the most effective plant-to-bacterium signal in the soybean (Glycine max (L.) Merr.) nitrogen fixation symbiosis, was used to pretreat Bradyrhizobium japonicum. We have previously reported that this increased soybean nodulation and nitrogen fixation in growth chamber studies. Two field experiments were conducted on two adjacent sites in 1994 to determine whether the incubation of B. japonicum with genistein, prior to application as an inoculant, or genistein, without B. japonicum, applied onto seeds in the furrow at the time of planting, increased soybean grain yield and protein yield in short season areas. The results of these experiments indicated that genistein-preincubated bradyrhizobia increased the grain yield and protein yield of AC Bravor, the later maturing of the two cultivars tested. Genistein without B. japonicum, applied onto seeds in the furrow at the time of planting also increased both grain and protein yield by stimulation of native soil B. japonicum. Interactions existed between genistein application and soybean cultivars, and indicated that the cultivar with the greatest yield potential responded more to genistein addition.     

Purification,partial characterization,and subcellular localization of a 38 kilodalton,calcium-regulated protein of Rhizobium fredii USDA208

Calcium is essential for the growth of rhizobia and the formation of nitrogen-fixing root-nodules on legumes, but its precise role in these processes remains unknown. We have found that Rhizobium fredii USDA208 accumulates a major 38 kDa protein when grown in media supplemented with 0.3–2 mM CaCl₂. We have purified this protein and raised polyclonal antibodies against it. The protein initially is synthesized as a 40 kDa precursor which subsequently undergoes calcium-dependent processing to give rise to the mature polypeptide. Subcellular and immunocytochemical localization studies indicate that the 38 kDa protein accumulates preferentially in the periplasmic space. Its N-terminal sequence, AETIKIGVAGPMTG, shows significant homology to the N-termini of amino acid binding proteins from the periplasm, including leucine-, isoleucine-, and valine-specific binding proteins of Pseudomonas aeruginosa and Escherichia coli and a leucine-specific binding protein of E. coli. The R. fredii protein does not, however, bind [³H]-leucine. The 38 kDa protein is encoded by the bacterial chromosome. It is absent in several rhizobia other than R. fredii, but antigenically related polypeptides are present in Escherichia coli and Erwinia carotovora subsp. carotovora.     

Potential for increasing biological nitrogen fixation in soybean

The importance of soybean as a source of oil and protein, and its ability to grow symbiotically on low-N soils, point to its continued status as the most valuable grain legume in the world. With limited new land on which to expand, and emphasis on sustainable systems, increases in soybean production will come mostly from increased yield per unit area. Improvements in biological nitrogen fixation can help achieve increased soybean production, and this chapter discusses research and production strategies for such improvement.The soybean-Bradyrhizobium symbiosis can fix about 300 kg N ha^-1 under good conditions. The factors which control the amount of N fixed include available soil N, genetic determinants of compatibility in both symbiotic partners and lack of other yield-limiting factors. Response to inoculation is controlled by the level of indigenous, competing bradyrhizobia, the N demand and yield potential of the host, and N availability in the soil.Research efforts to improve BNF are being applied to both microbe and soybean. While selection continues for effective, naturally occurring bradyrhizobia for inoculants and the use of improved inoculation techniques, genetic research on bradyrhizobia to improve effectiveness and competitiveness is advancing. Selection, mutagenesis and breeding of the host have focused on supernodulation, restricted nodulation of indigenous B. japonicum, and promiscuous nodulation with strains of bradyrhizobia from the cowpea cross-inoculation group. The research from the host side appears closer to being ready for practical use in the field.Existing knowledge and technology still has much to offer in improving biological nitrogen fixation in soybean. The use of high-quality inoculants, and education about their benefits and use can still make a significant contribution in many countries. The importance of using the best adapted soybean genotype with a fully compatible inoculant cannot be overlooked, and we need to address other crop management factors which influence yield potential and N demand, indirectly influencing nitrogen fixation. The implementation of proven approaches for improving nitrogen fixation in existing soybean production demands equal attention as received by research endeavours to make future improvements.     

Effect of the VAM fungus Glomus sp. on the growth and yield of soybean inoculated with Bradyrhizobium japonicum

The effect of two Bradyrhizobium japonicum strains (D344 and Urbana), on the frequency and intensity of infection by a VAM fungal Glomus sp. and the effect of VAM on biomass production by nodulating plants were tested in soybean growing in a soil containing low levels of accessible P and N. During the initial stage of vegetative growth, mycorrhiza frequency in roots inoculated with the two rhizobial strains did not differ. However, during flowering it was 178% higher in roots with the strain D344 than in the presence of the strain Ubrana. At final harvest (green pods) the VAM frequency did not differ in the presence of either strain. VAM positively affected biomass production, foliar concentrations of P, Zn and Cu, and number and dry matter yield of pods, but did not increase concentrations of total N and K. In nonmycorrhizal plants total nitrogenase activity (not nodule mass) and growth were higher with the rhizobial strain Urbana. The greatest nitrogenase activity, growth and yield occurred in the presence of the VAM fungus, and did not differ for plants with different strains of rhizobia.     

Characterization of a class of small auxin-inducible soybean polyadenylated RNAs

Four new auxin-responsive RNAs from soybean (Glycine max (L.) Merr., var. Wayne) are described. The RNAs were identified by hybridization to three cDNA probes obtained from a library enriched for sequences which increase in abundance within 60 min after 2,4-D (2,4-dichlorophenoxyacetic acid) treatment. These RNAs appear to define a new class of small (i.e. approximately 550 nucleotides) RNAs that respond extremely rapidly to application of exogenous auxin. In excised elongating hypocotyl sections, an increase in the abundance of these RNAs can be detected 2 to 5 min after treatment with 50 M 2,4-D. This response is half maximal after 10 min and reaches steady state in 60 min. RNA blot analysis shows that these RNAs are expressed differentially in various parts of the seedling. The degree of inducibility by auxin is also organ-specific, with the elongating hypocotyl being the most responsive of the organs tested. The RNAs display identical response specificities with one exception. Accumulation of one RNA, designated 10A, is completely abolished by simultaneous addition of cycloheximide and 2,4-D. This RNA also displays a different 2,4-D dose response than other RNAs examined. These results suggest that more than one mechanism is involved in rapid modulation of gene expression by auxin.     

Early seedling and seasonal N2-fixing symbiotic activity of two soybean [Glycine max (L.) Merr.] cultivars inoculated with Bradyrhizobium strains of diverse origin

In areas with a short growing season the poor adaptability of soybean [Glycine max Meer. (L.)] to cool soil conditions is considered the primary yield limiting factor. Soybean requires temperatures in the 25 to 30°C range for optimum N₂-fixation and yield. Field studies were conducted in 1990 and 1991 at Montreal, Quebec to determine whether adaptability to cool soil conditions, with respect to earlier symbiosis establishment and function, existed among either Bradyrhizobium strains or soybean genotypes. An early maturing isoline of the soybean cultivar Evans and the cultivar Maple Arrow were inoculated with one of four strains isolated from the cold soils of Hakkaido, northern Japan, or the commercially used strains 532C or USDA110, at two planting dates. Plot biomass and nodulation were assessed at seedling (V2), and flowering(R2) growth stages and harvest maturity. Soybean genotypes did not differ for pre-flowering nodulation or N₂-fixation in the cool spring conditions of the first year. Seasonal N₂-fixation rates were also determined at the final harvest by the N-balance and ¹⁵N-isotope dilution methods. Significantly higher symbiotic activity was found for two of the four Hakkaido strains and was reflected in higher final soybean seed yield and total N₂-fixation for the growing season, as compared to the two commercial strains. Planting 14 days earlier resulted in greater early vegetative and total seasonal N₂ fixation and yield in the second year when soil temperatures were warmer, emphasizing the need for the development of soybean-Bradyrhizobium combinations superior in nodule development and function under cool soil conditions.     

Characterization of a stress-induced,developmentally regulated gene family from soybean

We describe a family of stress-induced, developmentally regulated soybean genes for which cDNAs have been obtained from two different cultivars (Glycine max cv. Mandarin and Glycine max cv. Williams). The mRNAs corresponding to these cDNAs, called SAM22 and H4, respectively, accumulate predominantly in the roots of soybean seedlings but are present at high levels in the roots and leaves of mature plants. SAM22 accumulation is especially dramatic in senescent leaves. In addition, SAM22 accumulation can be induced in young leaves by wounding or by transpiration-mediated uptake of salicylic acid, methyl viologen, fungal elicitor, hydrogen peroxide or sodium phosphate (pH 6.9). Taken together, these data indicate that the genes corresponding to SAM22 and H4 are induced by various stresses and developmental cues. Southern blot analysis indicates that multiple copies of sequences related to SAM22 exist in the soybean genome. We also show that the nucleotide sequences of the cDNAs corresponding to SAM22 and H4 are 86% identical at the nucleotide level to each other and 70% identical at the amino acid level to the disease resistance response proteins of Pisum sativum.     

Correlations among leaf CO2-exchange rates,areas and enzyme activities among soybean cultivars

Soybean (Glycine max (L.) Merr.) genotypes varying in area per nodal unit (usually a trifoliolate) and maturity class were grown in plots at the University of Illinois experimental farm. Leaf CO₂-exchange rates per unit area (CER) were measured under sunlight on intact plants. In addition to previously reported correlations with specific leaf weight and chlorophyll, CER was positively correlated with ribulose bisphosphate carboxylase (RuBPcase) activity, specific activity, and soluble protein, and was negatively correlated with area per leaf unit. The CER: chlorophyll correlation was destroyed by high CER values in 2 chlorophyll-deficient lines. CER values for 27 of the 35 lines tested fell within the range of those for isolines of cultivar Clark varying in leaf characteristics. The CER values were highest for fully expanded leaves during rapid pod fill. These results suggested that photoperiod (maturity) genes and genes for leaf area growth interact with genes controlling photosynthetic CO₂-exchange to produce the major differences in CER values among soybean genotypes.     

Comparison of the host range of fast-growingR. japonicum strains with a fast-growing isolate from Lablab

Summary Fast-growingRhizobium japnicum strains derived from the People's Republic of China were compared with a fast-growingRhizobium isolate from Lablab for their ability to nodulate tropical legumes grown in Leonard-jars and test tube culture. Fast-growingR. japonicum strains were all effective to varying degrees in their symbiosis withVigna unguiculata. Two strains USDA 192 and USDA 201, effectively nodulatedGlycine whightii and one strain, USDA 193, effectively nodulatedMacroptilium atropurpureum. Other nodulation responses in tropical legumes were ineffective. The fast-growing isolate from Lablab was more promiscuous, effectively nodulating with a larger host range. The fast-growing Lablab strain was considered more akin, on a symbiotic basis, to the slow-growing cowpea type rhizobia than the fast-growing China strains ofR. japonicum whilst maintaining physiological characteristics of other fast-growing rhizobia.     

Fertile progeny of a hybridization between soybean [Glycine max (L.) Merr.] and G. tomentella Hayata

Summary A colchicine-doubled F₁ hybrid (2n=118) of a cross between PI 360841 (Glycine max) (2n=40) x PI 378708 (G. tomentella) (2n=78), propagated by shoot cuttings since January 1984, produced approximately 100 F₂ seed during October 1988. One-fourth of the F₂ plants or their F₃ progeny have been analyzed for chromosome number, pollen viability, pubescence tip morphology, seed coat color, and isoenzyme variation. Without exception, all plants evaluated possessed the chromosome number of the G. max parent (2n=40). Most F₂ plants demonstrated a high level of fertility, although 2 of 24 plants had low pollen viability and had large numbers of fleshy pods. One F₂ plant possessed sharp pubescence tip morphology, whereas all others were blunt-tipped. All evaluated F₂ and F₃ plants expressed the malate dehydrogenase and diaphorase isoenzyme patterns of the G. max parent and the endopeptidase isoenzyme pattern of the G. tomentella parent. Mobility variants were observed among progeny for the isoenzymes phosphoglucomutase, aconitase, and phosphoglucoisomerase. This study suggests that the G. Tomentella chromosome complement has been eliminated after genetic exchange and/or modification has taken place between the genomes.Journal Paper No. J-13776 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA, USA, Project 2763