Subtropical Legumes Research Articles

Insight into Genetic Diversity of Cultivated Lima Bean (<i>Phaseolus lunatus</i> L.) in Benin

Lima bean is a tropical and subtropical legume from the genus Phaseolus which is cultivated for its importance in food and in medicine, but which remains a Neglected and Underutilized Crop in Benin. Understanding the genetic diversity of a species’ genetic resources is useful for the establishment of appropriate conservation strategies and breeding programs and for sustainable use. We use 6 out of ten SSR markers to analyze the diversity and population structure of 28 Lima bean landraces collected in Benin. A total of 28 alleles with an average of 4.16 alleles per SSR were amplified. The Polymorphic Information Content value ranged from 0.079 to 0.680 with an average of 0.408. The analysis of population structure revealed three subpopulations. PCoA revealed three well-separated clusters among the analyzed accessions in accordance with the population structure results and the clustering based on the Neighbor-Joining tree. AMOVA showed highly significant (p = 0.001) diversity among and within populations. Hence, 32% of the genetic variation was distributed among the population and 68% was distributed within populations. A high PhiP value (0.321) was found between the three sub-subpopulations indicating a high genetic differentiation between these sub-subpopulations. By exhibiting the highest average number of alleles, Shannon-Weaver information and Shannon-Weaver diversity indices, and the highest mean number of private alleles, subpopulation 1 is the main gene pool of the analyzed collection. The present study is an important starting point for the establishment of appropriate conservation strategies and breeding programs for Lima bean genetic resources.

Genome-wide association study in accessions of the mini-core collection of mungbean (Vigna radiata) from the World Vegetable Gene Bank (Taiwan)

BackgroundMungbean (Vigna radiata (L.) R. Wilczek, or green gram) is important tropical and sub-tropical legume and a rich source of dietary protein and micronutrients. In this study we employ GWAS to examine the genetic basis of variation in several important traits in mungbean, using the mini-core collection established by the World Vegetable Center, which includes 296 accessions that represent the major market classes. This collection has been grown in a common field plot in southern European part of Russia in 2018.ResultsWe used 5041 SNPs in 293 accessions that passed strict filtering for genetic diversity, linkage disequilibrium, population structure and GWAS analysis. Polymorphisms were distributed among all chromosomes, but with variable density. Linkage disequilibrium decayed in approximately 105 kb. Four distinct subgroups were identified within 293 accessions with 70% of accessions attributed to one of the four populations. By performing GWAS on the mini-core collection we have found several loci significantly associated with two important agronomical traits. Four SNPs associated with possibility of maturation in Kuban territory of Southern Russia in 2018 were identified within a region of strong linkage which contains genes encoding zinc finger A20 and an AN1 domain stress-associated protein.ConclusionsThe core collection of mungbean established by the World Vegetable Center is a valuable resource for mungbean breeding. The collection has been grown in southern European part of Russia in 2018 under incidental stresses caused by abnormally hot weather and different photoperiod. We have found several loci significantly associated with color of hypocotyl and possibility of maturation under these stressful conditions. SNPs associated with possibility of maturation localize to a region on chromosome 2 with strong linkage, in which genes encoding zinc finger A20 and AN1 domain stress associated protein (SAP) are located. Phenotyping of WorldVeg collection for maturation traits in temperate climatic locations is important as phenology remains a critical breeding target for mungbean. As demand rises for mungbean, production in temperate regions with shorter growing seasons becomes crucial to keep up with needs. Uncovering SNPs for phenology traits will speed breeding efforts.

Distance‐dependent effects of pathogenic fungi on seedlings of a legume tree: impaired nodule formation and identification of antagonistic rhizosphere bacteria

Summary The Janzen‐Connell (JC) hypothesis proposes that diversity of tree communities is promoted by species‐specific enemies that suppress seedling recruitment. Pathogenic soil‐borne fungi are often responsible for JC effects. However, previous ecological studies have not placed JC effects in the context of beneficial soil bacteria. Using the JC effect surrounding a subtropical legume tree (Ormosia glaberrima) as a model, we characterized tripartite interactions between seedlings, soil fungi and plant‐associated bacteria. Survival of seedlings grown in soil inocula collected at close distances to focal adult trees was reduced. Half of the experimental units were treated with fungicides to confirm the presence of pathogenic fungi. In a parallel experiment, nitrogen‐fixing rhizobia induced fewer nodules on O. glaberrima seedlings when soil inocula were collected closer to focal adult trees. An inoculation experiment with rhizobial isolates promoted nodulation of seedlings grown in soil taken at close distances to adult trees, suggesting that rhizobial densities are suboptimal at these locations. Fusarium oxysporum, a pathogen of O. glaberrima seedlings, produced exudates that inhibited growth of most bacteria isolated from nodules. Accordingly, F. oxysporum negatively affected rhizosphere colonization of rhizobia in a co‐inoculation experiment. Contrariwise, certain Burkholderia isolates (from nodules and the rhizosphere) were identified that possess the ability to inhibit growth of F. oxysporum. The majority of the antagonistic bacteria were isolated from locations with fungal pathogens, suggesting competition between fungi and rhizosphere bacteria. Exclusion of pathogenic fungi by application of fungicides promoted nodulation of O. glaberrima seedlings under growth‐room and field conditions. Synthesis. Our findings indicate that soil‐borne pathogens surrounding adult trees are microbial keystone species that locally influence interactions between seedlings and plant‐associated bacteria.

Transporters involved in source to sink partitioning of amino acids and ureides: opportunities for crop improvement

In most plant species, amino acids are the predominant chemical forms in which nitrogen is transported. However, in nodulated tropical or subtropical legumes, ureides are the main nitrogen transport compounds. This review describes the partitioning of amino acids and ureides within the plant, and follows their movement from the location of synthesis (source) to the sites of usage (sink). Xylem and phloem connect source and sink organs and serve as routes for long-distance transport of the organic nitrogen. Loading and unloading of these transport pathways might require movement of amino acids and ureides across cell membranes, a task that is mediated by membrane proteins (i.e. transporters) functioning as export or import systems. The current knowledge on amino acid and ureide transporters involved in long-distance transport of nitrogen is provided and their importance for source and sink physiology discussed. The review concludes by exploring possibilities for genetic manipulation of organic nitrogen transporter activities to confer increases in crop productivity.

Response of Axonopus catarinensis and Arachis pintoi to shade conditions

In the northeast of Argentina, there are more than 100,000 ha of silvopastoral systems, where trees, forages and livestock are combined with the goal to diversify income, reduce financial risk, obtain more profit and enhance environmental benefit (Cubbage et al. 2012). The rapid adoption of these production systems by farmers has generated high demand for information on shade-tolerant forage grass and legume species. Axonopus catarinensis is a native grass from Itajai Valley (Brazil), that was introduced to the northeast of Argentina 10 years ago, and Arachis pintoi is a subtropical legume (also native to Brazil) adapted to acid soils and tolerant of medium levels of shade (Fisher and Cruz 1994). Visual observation of these species in the field indicated high yields and acceptable tolerance to shade. A trial was subsequently carried out with the aim to quantify dry matter yield and nutritive quality of the species under different levels of shade for silvopastoral use.

Diversity and symbiotic effectiveness of beta-rhizobia isolated from sub-tropical legumes of a Brazilian Araucaria Forest

While the occurrence of Betaproteobacteria occupying the nodules of tropical legumes has been shown, little is known about subtropical areas. Araucaria Forest is a subtropical endangered ecosystem, and a better understanding of the legume-rhizobial symbionts may allow their use in land reclamation. The 16S rRNA gene of bacteria isolated from nine leguminous species was sequenced and their nodulation tested in Mimosa scabrella and Phaseolus vulgaris. 196 isolates were identified as eight genotypes: Pantoea, Pseudomonas, Bradyrhizobium sp1-2, Rhizobium, and Burkholderia sp1-3. The majority of the isolates from native plants (87%) were taxonomically related to β-rhizobia, namely Burkholderia, however the legumes Galactiacrassifolia and Collea speciosa were nodulated by both α and β-rhizobia, and Acacia dealbata, an exotic plant, only by α-rhizobia. The nifH genes of some isolates were sequenced and N-fixing potential shown by the acetylene reduction test. Most of the isolates nodulated the test plants, some were effective in M. scabrella, but all presented low efficiency in the exotic promiscuous legume P. vulgaris. Pantoea and Pseudomonas did not nodulate and probably are endophytic bacteria. The presented data shows diversity of α, β and γ-Proteobacteria in nodules of subtropical legumes, and suggests host specificity with β-rhizobia. Potential isolates were found for M. scabrella, indicating that a high N-fixing strain may be further inoculated in plants for use in reforestation.

Virus diseases of perennial pasture legumes in Australia: incidences, losses, epidemiology, and management

This article reviews current knowledge for Australia over the occurrence, losses caused, epidemiology, and management of virus diseases of perennial pasture legumes. Currently, 24 viruses have been found infecting perennial pasture legumes, and one or more viruses have been detected in 21 of these species. These viruses are transmitted by insect vectors, non-persistently or persistently, by contact or via seed. Their modes of transmission are critical factors determining their incidences within pastures in different climatic zones. Large-scale national or state surveys of lucerne (alfalfa) (Medicago sativa) and white clover (Trifolium repens) pastures revealed that some viruses reach high incidences. Infection with Alfalfa mosaic virus (AMV) was very widespread in lucerne stands, and with AMV and White clover mosaic virus (WClMV) in white clover pastures. Several other viruses are potentially important in pastures in these and other perennial temperate/Mediterranean pasture species. Data demonstrating herbage yield losses, diminished pasture persistence, and impaired nitrogen fixation/nodule function are available for AMV in lucerne, and AMV, WClMV, and Clover yellow vein virus in white clover. Integrated Disease Management approaches involving phytosanitary, cultural, chemical, and host resistance control measures are available to minimise virus infection in lucerne and white clover. Research on virus diseases of perennial tropical–subtropical pasture legumes has focussed almost entirely on virus identification, and information on their incidences in pastures, the losses they cause, and how to control them is lacking. Overall, viruses of perennial pasture legumes are least studied in South Australia and the Northern Territory. These and other critical research and development gaps that need addressing are identified.

Effect of competition from a C4 grass on the phosphorus response of a subtropical legume

Tropical pasture systems are typically dominated by C4 grasses growing on nitrogen (N) deficient soils. Under these conditions, N2-fixing legumes should have a competitive advantage, yet low legume contents are often reported in these systems. This work investigates whether below-ground competition for phosphorus (P) is limiting the ability of legumes to compete in swards of C4 grasses when grown in a sand matrix. The external P requirement of a subtropical legume (butterfly pea, Clitoria ternatea L.) and a C4 grass (buffel grass, Cenchrus ciliaris L.) were initially determined in a P-response experiment. Four rates of P (4.6–78.2 mg P kg–1 of Colwell P) were subsequently selected to investigate the growth response of the butterfly pea when grown with and without competition from a sward of N-deficient buffel grass. Shoot dry matter was determined over successive cuts and P uptake determined at the final harvest at 72 days. Buffel grass dominated the mixed swards and reduced the shoot dry matter production of the butterfly pea by >50% relative to the pure swards. A significant difference in the soil P response curve and shoot P uptake of butterfly pea was not detected between pure swards and those with competition from buffel grass. The ability of C4 grasses to acquire and convert resources (i.e. light, water and nutrients) more efficiently into shoot dry matter is likely to be a major factor resulting in grass-dominated pastures in tropical systems.

Distribution of isoflavones and coumestrol in neglected tropical and subtropical legumes

Isoflavones and coumestrol from dietary legumes are plant constituents showing multiple beneficial effects on humans. Owing to their ability to bind with mammalian estrogenic receptors and thereby intervention in several kinds of hormone-related cancers, they have received much attention. Soybean (Glycine max) is currently the major source of isoflavonoids in human diet. However, dozens of tropical and subtropical leguminous species remain unexplored for their isoflavonoids content. We have analyzed 55 extracts from 41 tropical and subtropical legume species used either in human or animal diet by high-performance liquid chromatography for the content of soy isoflavones, biochanin A, daidzein, daidzin, formononetin, genistein, genistin, sissotrin, ononin and the coumestan coumestrol. Genistein and biochanin A were the most abundant compounds. The highest content of genistein was found in aerial parts of Andira macrothyrsa, seeds of Pachyrhizus tuberosus and aerial parts of Calopogonium mucunoides (598, 250 and 184 µg g(-1), respectively) and biochanin A in aerial parts of Cratylia argentea, C. mucunoides and flowers of A. macrothyrsa (76, 53 and 40 µg g(-1), respectively). None of the samples tested was richer overall source of soy isoflavones and coumestrol than soybean; nevertheless several species (C. mucunoides or A. macrothyrsa) may serve as a promising source of individual compounds.

Breeding for disease resistance, forage, and seed production in Lotononis bainesii Baker

In 1999, INIA Uruguay initiated a plant breeding program on Lotononis bainesii Baker, a subtropical forage legume from Southern Africa. Seeds from nine different geographical origins were grown and subsequently hand‐crossed. Ninety crosses were generated and their variability was used to improve disease resistance, and forage and seed yield. Fusarium oxysporum, a fungal pathogen responsible for crown and stolon rot, is common in Uruguayan soils and the only public cultivar available is reported to be susceptible to this pathogen. In winter 2001, a seedling screening method was used that allowed seeds to grow in Petri plates in the presence of the fungus. The resistant plants of each of the 90 crosses were transplanted into trays in a naturally lit glasshouse and subsequently divided into three sets with equal representation. Two of them were transplanted as spaced plant nurseries into each of two sites with distinct soil types in the basaltic region of Uruguay. The third set was transplanted into 10‐litre pots to select for seed production. The best 17 crosses were selected based on their performance in forage and seed yield evaluations. In this paper we present the breeding methodology used in developing the cultivar ‘INIA Glencoe’ with improved disease resistance and improved forage and seed production. Preliminary tests conducted in 2003 to compare the new cultivar ('INIA Glencoe') with the public one ('Miles') demonstrated that ‘INIA Glencoe’ has superior disease resistance as well as enhanced forage and seed yield.

Reproductive and Molecular Evidence for Allogamy in Lotononis bainesii Baker

Reproductive characteristics can influence seed production and the amount and distribution of genetic variation within populations. Lotononis bainesii Baker is a subtropical forage legume from southern Africa that earlier researchers reported as having a cleistogamous form of reproduction. More recent reports suggest that species in the genus Lotononis Section Listia reproduce chasmogamously. Research from this study suggests that this species needs pollinators to produce seed and that genotypes exist that are self‐incompatible. The use of sequence characterized amplified regions (SCAR) and cleaved amplified polymorphic sequence (CAPS) markers demonstrated that L. bainesii is highly allogamous.

Germination response to temperature in tropical and subtropical pasture legumes. 2. Alternating temperature

The germination response of 8 promising and commonly used tropical and subtropical legumes in northern Australia was tested at a range of alternating temperatures. Except at temperatures <20°C or >36°C, total germination was largely unaffected by different alternating temperatures. Although there were statistically significant differences between constant and alternating temperatures, overall, these differences were <2% and hence of no biological importance. Increasing amplitude of fluctuation in temperature decreased the rate of germination for some species. At 8°C amplitude Glycine latifolia, Macroptilium atropurpureum and Lablab purpureus showed no difference in the time taken to reach 50% of germination while Chamaecrista rotundifolia, Stylosanthes scabra and Desmanthus virgatus took 1.5-2 times as long as at constant temperature. Predicted germination against real time, using 2 different models, fitted the observed data poorly. In particular, prediction of the commencement of germination was poor for C. rotundifolia and S. scabra. This failure at more extreme or highly fluctuating temperatures indicates that further development is required before the models would be sufficiently reliable for inclusion in simulation models of legume persistence. In particular, the rate of death of seeds at temperatures distant from the optimum range needs to be included. The ability to germinate at a broad range of temperatures indicates that the species are well adapted to northern Australia. Some species may be susceptible to large fluctuations in temperature during germination, and this should be considered in criteria for selecting future species.

Germination response to temperature in tropical and subtropical pasture legumes. 1. Constant temperature

The germination response of 13 promising and commonly used tropical and subtropical legumes in northern Australia was tested in the laboratory at 10 constant temperatures ranging from 8 to 447deg;C. Total percent germination for most species was high at temperatures from 16 to 36°C, with Macroptilium atropurpureum, Lablab purpureus and Glycine latifolia germinating well at 12°C. Macroptilium atropurpureum and G. latifolia had less seed death than other species at 8°C. There was no germination at 8 or 44°C for any species. Optimum temperature for rate of germination ranged from 24°C for G. latifolia up to 36°C for Macroptilium bracteatum. Leucaena leucocephala showed a 12-degree range (24-36°C) of optimum temperatures for rate of germination, but most species had a range of 4-8°C. The ability to germinate at a broad range of temperatures indicates that the species are well adapted to northern Australia. Consideration of these responses could be useful in selection of future species or cultivars. Existing linear models with base, optimum and ceiling temperatures, and coefficients of germination rate above and below optimum temperature were tested to predict germination from thermal time. Predicted germination in real time explained 73-90% of the variation in observed germination, with the closeness of fit poor at temperatures distant from optimum. Models using a series of step-wise linear equations describing each 5% interval of germination explained over 99% of the variation in cumulative germination with time, but required a large number of parameters.

Variability in yield and yield component responses to genistein pre-incubated Bradyrhizobium japonicum by soybean [Glycine max (L.) Merr] cultivars

The sub-tropical legume, soybean [Glycine max (L.) Merr.], has lower grain yields at low temperatures, mainly due to reduced nitrogen fixation. The isoflavone genistein has been identified as one of the major compounds in soybean seed and root extracts responsible for inducing the expression of the B. japonicum nod genes. A 2-year field study was conducted in 1997 and 1998 with 11 soybean cultivars recommended for Quebec, and representing a range of yield potentials and maturity groups. The objective of this study was to assess the variability among soybean cultivar maturity groups in terms of response to genistein application under Canadian short season and cool-spring conditions. The experiments were organized in a randomized complete block design with three replications. The two genistein treatments included B. japonicum inoculant pre-incubated with 20 μm genistein and B. japonicum inoculant only. The inoculants were applied into the furrow at the time of planting. The results of this study showed that genistein pre-incubated B. japonicum increased soybean grain yield and protein content over two years. In 1998, pod number per plant−1 and seed number plant−1 were also clearly increased. When 20 μm genistein was applied in 1998, cultivars in the late maturity group had 28 and 70% more shoot and total protein content, respectively, than the early maturity groups with or without genistein, or the late maturity without genistein, in 1998. There was no interaction between genistein application and soybean cultivar in this study, indicating that both early and late maturing cultivars responded similarly to genistein pretreated inocula. Pre-incubation of B. japonicum with genistein can increase N2 fixation potential in short season areas. Key words: Soybean, cultivars, genistein, yield, and yield components

Nitrogen fixation and nitrate metabolism for growth of six diverse soybean [ Glycine max. (L.) Merr.] genotypes under low temperature stress

Soybean [ Glycine max (L.) Merr] is a subtropical legume that is at the northern limit of its range in the cool temperate zone of North America. Low temperature stress inhibits N 2 fixation and NO 3 metabolism in soybean. A controlled environment experiment was conducted to test the effects of low temperature stress (16/9°C day/night versus 26/19°C) on N 2 fixation and NO 3 metabolism of one American, one northern Chinese, one Polish, one Swedish and two Canadian soybean cultivars. The objectives of this work were to measure variability in N 2 fixation, NO 3 use, and plant growth under low and optimal temperature regimes among these diverse genotypes, and to determine the physiological bases for these differences. The results showed that: (1) the relative ranking of cultivars for growth and accumulation is different between nitrogen sources under optimal or suboptimal temperatures; (2) the cultivars which are better able to fix N 2 usually have more nodule mass; (3) the plants which fix more N 2 allocate less photosynthate to the plant root system, and (4) there was no negative relationship between N 2 fixation or NO 3 utilization among the cultivars tested.

Adaptation of Pigeonpea (Cajanus cajan Millsp.) to a Loamy Sand Site in Minnesota

Pigeonpea, a subtropical legume, was successfully grown in a high-latitude (≈45°N) environment. Four short-season pigeonpea accessions from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) were subjected to three cycles of pedigree selection. Performance trials (175,000 plants/ha) were conducted on loamy sand with dryland and irrigated sites in 1991 and 1992. Thirty-eight S3-derived lines from ICRISAT ICPL 83004 were used in both years and seven S3-derived lines from ICRISAT P 2125 and ICRISAT ICPL 85010 were added the second year. Differences (P ≤ 0.05) in seed yield (kg·ha–1) were observed among the S3 lines, with a maximum yield of 1468 kg·ha–1. The lines also differed (P ≤ 0.05) for harvest index (HI), calculated as the ratio of seed yield to shoot total dry matter (TDM) with a maximum of 0.48 (line MF-26). Dryland seed yield was strongly correlated with TDM (r2 = 0.98), HI (r2 = 0.92), and early bloom (r2 = 0.76). In a time-of-planting comparison of seven lines in 1992, seed yield was highest (754 kg·ha–1) at the earliest (29 Apr.) planting date and declined progressively to 178 kg·ha–1 at the latest (2 June) planting date, while HI decreased from 0.42 to 0.12. Plants were shorter at maturity in the earliest planting date.

Root zone temperature sensitivity of nitrogen fixing and nitrate-supplied soybean [ Glycine max (L.) Merr. cv maple arrow] and lupin ( Lupinus albus L. cv ultra) plants

Soybean [ Glycine max (L.) Merr.] is a subtropical legume that is now often grown in cool temperate areas. Under these conditions, low root zone temperatures (RZT) may adversely affect N 2 fixation and therefore the growth and development of soybean plants. Lupin ( Lupinus albus L.), is well adapted to cool temperature areas. Soybean exports N from root nodules as ureides, while lupin exports N as amides. The water solubility of ureides declines sharply with temperature while the solubility of amides is much less affected. Experiments were established to test the effect of suboptimal RZT on N accumulation, N partitioning and dry matter partitioning by N 2-fixing and mineral N-supplied soybean and lupin plants. In the first experiment, soybean plants were grown at four constant RZT: 10, 15, 20 and 25°C with constant 25°C air temperature. Four nitrogen (N) treatments were applied within each RZT; plants were fertilized with a complete N-free nutrient solution supplemented with either 0, 7.1 or 14.2 mM N, or received 14.2 mM N at the onset of the experiment with this level being gradually decreased to zero over the first 15 days of the experiment. In a second experiment, soybean and lupin were grown at 10, 15, 20 and 25°C RZT and received either 0 or 14.2 mM N. Nitrogen accumulation and partitioning were more affected by low RZT in N 2-fixing than in mineral N-supplied soybean and lupin plants. Dry matter accumulation of N 2-fixing soybean plants was also more sensitive to low RZT than was that of mineral N-supplied soybean plants. The slower development of the N 2-fixing soybean plants at RZT less than 25°C was attributed to poor nodule development at temperatures in the 10°C range and to low nitrogenase activity at temperatures greater than 15°C. Data from the final harvest indicated that photosynthate shortage may have played a role in the reduced N 2 fixation. Lupin had a higher tissue N concentration than soybean at low RZT and a lower root to shoot per cent N ratio, but N 2 fixation in lupin seemed to be about as sensitive to low RZT as that of soybean.

Survival of Seeds of Tropical Grassland Species Subjected to Bovine Digestion

The survival and digestion of seeds of 47 tropical and subtropical legume and grass species were studied by placing the seeds in nylon bags in the rumen of fistulated cattle, followed by acid-pepsin digestion, to identify any differences likely to affect dissemination by grazing cattle. Seeds of only four of the 23 grass species survived in appreciable numbers. Digestion for short periods actually increased germination of Digitaria ciliaris, Axonopus affinis and Paspalum notatum while seeds of Pennisetum clandestinum survived up to 10 days in the rumen. All four are creeping, sward-forming species adapted to heavy grazing. Few seeds of the tall tussock grasses survived the digestive processes. Survival of legume seeds was closely related to the hard seed content of the sample (...)

Nitrogen fixation ability of exopolysaccharide synthesis mutants of Rhizobium sp. strain NGR234 and Rhizobium trifolii is restored by the addition of homologous exopolysaccharides.

Several transposon Tn5-induced mutants of the broad-host-range Rhizobium sp. strain NGR234 produce little or no detectable acidic exopolysaccharide (EPS) and are unable to induce nitrogen-fixing nodules on Leucaena leucocephala var. Peru or siratro plants. The ability of these Exo- mutants to induce functioning nodules on Leucaena plants was restored by coinoculation with a Sym plasmid-cured (Nod- Exo+) derivative of parent strain NGR234, purified EPS from the parent strain, or the oligosaccharide from the EPS. Coinoculation with EPS or related oligosaccharide also resulted in formation of nitrogen-fixing nodules on siratro plants. In addition, an Exo- mutant (ANU437) of Rhizobium trifolii ANU794 was able to form nitrogen-fixing nodules on white clover in the presence of added EPS or related oligosaccharide from R. trifolii ANU843. These results demonstrate that the absence of Rhizobium EPSs can result in failure of effective symbiosis with both temperate and subtropical legumes.

Small-plot studies ofDesmodium intortum(Mill.) Urb. cv. ‘Greenleaf’,D. uncinatum(Jacq.) DC. cv. ‘Silverleaf’, andLotononis bainesiiBaker cv. ‘Miles’, in Northland, New Zealand

Abstract Establishment and subsequent dry matter productivity of three subtropical legume species Desmodium intortum cv. ‘Greenleaf’, D. uncinatum cv. ‘Silverleaf’, and Lotononis bainesii cv. ‘Miles’ were compared with that of Lotus pendunculatus cv. ‘Commercial’ at two sites in Northland from 1971–74. Late December sowings resulted in successful establishment of both Desmodium species at the two sites. The establishment of Lotononis and Lotus was variable between sites and generally less than that of the Desmodiums. D. uncinatum yielded most at the northern site over the growing season, although D. intortum was higher yielding at the Southern site. Maximum growth rates for D. uncinatum were 45 kg DM/ha/day, although yields appeared to be limited by moisture stress and low minimum temperatures over the growing season at both sites. D. uncinatum, more so than D. intortum, was higher yielding when cut at 42-day intervals than when cut at 21-day intervals at the Northern site. Cutting interval had little effect on yields of Lotononis or Lotus at either site or on Desmodium yields at the Southern site. It is concluded that Lotononis, because of lack of persistence, has little potential as a pasture legume, and that although both Desmodium species were equal to or better than Lotus, their potential is likely to be limited by summer-autumn moisture stress, low minimum temperatures, and special management requirements over the growing season in Northland.