Mutation breeding of grain legumes

Genetic variation among existing cultivars and in germplasm collections is the outcome of selection during evolution and plant breeding. Mutagenesis offers the plant breeder a chance to tackle unconventional objectives, particularly those that were at a selection disadvantage in the past. Effective mutagens are available, but the bottleneck is the effective selection of rare desired variants from large mutagenized populations. Selection methods must be non-destructive. Grain legume mutation breeding has already led to improved cultivars with higher yield, better grain quality, or stronger resistance to pathogenens. Many mutations affecting nitrogen fixation related traits have also been reported. Some could be useful in breeding better cultivars, but the majority are being used to study the factors interacting in the complex process of symbiotic nitrogen fixation and to improve the strategy for producing cultivars with better fixation capacity.     

Carbon and nitrogen nutrition of nodulated roots of grain legumes

Abstract The spatial and temporal relationships between carbon (C) metabolism and nitrogen (N) nutrition in grain legumes are of great academic interest with the added bonus that any data for economically important species may ultimately prove useful to breeders and growers. So far there are no data which can be used to relate differences in carbon usage by any symbiotic association with differences in economic yield. Much research has focussed on the dependence of dinitrogen fixation on photosynthate supply, on the C–N relationships of nodulated roots and nodules and on diurnal and seasonal profiles of dinitrogen fixation. In all these aspects a plethora of responses have been described, often based on insufficiently proven measurement techniques; consequently unequivocal conclusions cannot be drawn. We know little about within-species differences due to cultivar, strain of Rhi-zobium or environment, or about the proportions of any heritable variations which might be sufficiently large to merit inclusion among the selection criteria of grain legume breeders.     

Quantifying below-ground nitrogen of legumes

Quantifying below-ground nitrogen (N) of legumes is fundamental to understanding their effects on soil mineral N fertility and on the N economies of following or companion crops in legume-based rotations. Methodologies based on ¹⁵N shoot-labelling with subsequent measurement of ¹⁵N in recovered plant parts (shoots and roots) and in the root-zone soil have proved promising. We report four glasshouse experiments with objectives to develop appropriate protocols for in situ ¹⁵N labelling of the four legumes, fababean (Vicia faba), chickpea (Cicer arietinum), mungbean (Vigna radiata) and pigeonpea (Cajanus cajan). Treatments included ¹⁵N-urea concentration (0.1–2.0% w/w), feeding technique (leaf-flap and petiole), leaflet/petiole position (top and bottom of shoot) and frequency of feeding (one and two occasions). ¹⁵N-labelling via the leaf-flap was best for fababean, mungbean and pigeonpea, whilst petiole feeding was best for chickpea, in all cases at the lower-stem nodes 3 or 4 using 0.2 mL volumes of 0.5% urea (98 atom% ¹⁵N excess). Fed leaflets and petioles were removed within 2 weeks of labelling. Uneven ¹⁵N enrichment of the nodulated roots because of effects of the less-enriched nodules meant that root derived N in soil would be overestimated if recovered roots were more heavily nodulated than unrecovered roots. One possible solution would be to assume crown nodulation of the plants. Thus, recovered roots would be nodulated; root-derived N remaining in soil may be without nodules. The ratios of nodulated root to unnodulated root enrichments could then be used as an adjustment in the calculations, i.e. in the case of fababean and chickpea, by dividing calculated root-derived N in soil by 1.12 (fababean) and 1.56 (chickpea).     

Methods for measuring biological nitrogen fixation in grain legumes

To assure proper management and fully realize the benefits of the legume-Rhizobium symbiosis it is necessary to be able to quantify the amount of nitrogen fixed. Having measured the effectiveness of atmospheric N₂ fixation the macro- or micro-symbionts as well as agronomic factors can be manipulated with the objective to maximize biological nitrogen fixation. A suitable method to quantify nitrogen fixation is therefore necessary in any programme aiming at increasing N₂ fixation, like the one being reported in this volume. There are several methods available to quantify nitrogen fixation and most of the commonly used ones are described in the present paper listing their advantages and disadvantages.     

Nitrogen nutrition of seedling grain legumes: some taxonomic, morphological and physiological constraints

Abstract The growth of young plants of the epigeal species Phaseolus vulgaris and Glycine max is compared with that of the hypogeal species Pisum sativum and Vicia faba, with particular reference to synchronization between the exhuastion of seed reserves of N and the availability of fixed N. It is argued that the N stress symptoms which occur when these two processes are not synchronized are more common and obvious in Phaseolus or Glycine than in Pisum or Vicia. This is primarily because in these species (a) the first fixed N is used for nodule growth rather than being exported to the shoot system and (b) the first foliage leaves have a much greater area and contain a larger proportion of N reserves from the seed. It is further suggested that Phaseolus and Glycine may show the greater response to nitrogen fertilizer applied at sowing since (a) most of the applied nitrate is passed directly to the shoots (rather than being reduced in the roots as in Pisum or Vicia) and (b) in addition to being used for growth (following reduction), it may also be used prior to reduction as part of the osmotic force driving cell expansion.     

The presence of nitrogen fixing legumes in terrestrial communities: Evolutionary vs ecological considerations

Nitrogen is often a limiting factor to net primary productivity (NPP) and other processes in terrestrial ecosystems. In most temperate freshwater ecosystems, when nitrogen becomes limiting to NPP, populations of N-fixing cyanobacteria experience a competitive advantage, and begin to grow and fix nitrogen until the next most limiting resource is encountered; typically phosphorus or light. Why is it that N-fixing plants do not generally function to overcome N limitation in terrestrial ecosystems in the same way that cyanobacteria function in aquatic ecosystems? To address this question in a particular ecosystem, one must first know whether the flora includes a potential set of nitrogen fixers. I suggest that the presence or absence of N-fixing plant symbioses is foremost an evolutionary consideration, determined to a large extent by constraints on the geographical radiation of woody members of the family Fabaceae. Ecological factors such as competition, nutrient deficiencies, grazing and fire are useful to explain the success of N-fixing plants only when considered against the geographical distribution of potential N-fixers.     

Factors regulating the contributions of fixed nitrogen by pasture and crop legumes to different farming systems of eastern Australia

On-farm and experimental measures of the proportion (%Ndfa) and amounts of N₂ fixed were undertaken for 158 pastures either based on annual legume species (annual medics, clovers or vetch), or lucerne (alfalfa), and 170 winter pulse crops (chickpea, faba bean, field pea, lentil, lupin) over a 1200 km north-south transect of eastern Australia. The average annual amounts of N₂ fixed ranged from 30 to 160 kg shoot N fixed ha^–1 yr^–1 for annual pasture species, 37–128 kg N ha^–1 yr^–1 for lucerne, and 14 to 160 kg N ha^–1 yr^–1 by pulses. These data have provided new insights into differences in factors controlling N₂ fixation in the main agricultural systems. Mean levels of %Ndfa were uniformly high (65–94%) for legumes growing at different locations under dryland (rainfed) conditions in the winter-dominant rainfall areas of the cereal-livestock belt of Victoria and southern New South Wales, and under irrigation in the main cotton-growing areas of northern New South Wales. Consequently N₂ fixation was primarily regulated by biomass production in these areas and both pasture and crop legumes fixed between 20 and 25 kg shoot N for every tonne of shoot dry matter (DM) produced. Nitrogen fixation by legumes in the dryland systems of the summer-dominant rainfall regions of central and northern New South Wales on the other hand was greatly influenced by large variations in %Ndfa (0–81%) caused by yearly fluctuations in growing season (April–October) rainfall and common farmer practice which resulted in a build up of soil mineral-N prior to sowing. The net result was a lower average reliance of legumes upon N₂ fixation for growth (19–74%) and more variable relationships between N₂ fixation and DM accumulation (9–16 kg shoot N fixed/t legume DM). Although pulses often fixed more N than pastures, legume-dominant pastures provided greater net inputs of fixed N, since a much larger fraction of the total plant N was removed when pulses were harvested for grain than was estimated to be removed or lost from grazed pastures. Conclusions about the relative size of the contributions of fixed N to the N-economies of the different farming systems depended upon the inclusion or omission of an estimate of fixed N associated with the nodulated roots. The net amounts of fixed N remaining after each year of either legume-based pasture or pulse crop were calculated to be sufficient to balance the N removed by at least one subsequent non-legume crop only when below-ground N components were included. This has important implications for the interpretation of the results of previous N₂ fixation studies undertaken in Australia and elsewhere in the world, which have either ignored or underestimated the N present in the nodulated root when evaluating the contributions of fixed N to rotations.     

豆科植物共生结瘤的分子基础和调控研究进展

豆科植物与根瘤菌共生互作的结果导致了一个新的植物器官――根瘤的形成, 根瘤菌生活在根瘤中, 它们具有将氮气转化为能被植物同化的氨的能力。该文阐述了根瘤的形成过程和类型, 并主要以模式豆科植物蒺藜苜蓿(Medicago truncatula)和日本百脉根(Lotus japonicus)为例, 对近年来共生结瘤过程中宿主植物对根瘤菌结瘤因子的识别和信号传递、侵入线形成和固氮的分子基础, 以及宿主植物对根瘤形成的自主调控机制、环境中氮素营养对结瘤的影响研究进行了综述, 指出当前豆科植物与根瘤菌共生互作研究存在的问题, 并对今后的研究方向作了分析与展望。     

Sustainable agriculture in the semi-arid tropics through biological nitrogen fixation in grain legumes

Sustainable agriculture relies greatly on renewable resources like biologically fixed nitrogen. Biological nitrogen fixation plays an important role in maintaining soil fertility. However, as BNF is dependent upon physical, environmental, nutritional and biological factors, mere inclusion of any N₂-fixing plant system does not guarantee increased contributions to the soil N pool. In the SAT where plant stover is also removed to feed animals, most legumes might be expected to deplete soil N. Yet beneficial legume effects in terms of increased yields in succeeding cereal crops have been reported. Such benefits are partly due to N contribution from legumes through BNF and soil N saving effect. In addition, other non-N rotational benefits, for example, improved nutrient availability, improved soil structure, reduced pests and diseases, hormonal effects are also responsible. In this paper we have reviewed the research on the contribution of grain legumes in cropping systems and the factors affecting BNF. Based on the information available, we have suggested ways for exploiting BNF for developing sustainable agriculture in the semi-arid tropics (SAT). A holistic approach involving host-plant, bacteria, environment and proper management practices including need based inoculation for enhancing BNF in the cropping systems in the SAT is suggested.     

抗生素产生菌诱变育种的研究进展

一种抗生素能否产业化决定于抗生素产生菌菌种的产素水平。因而如何提高抗生素产生菌的产素水平成为抗生素研究工作者长期不懈探索的重要课题。其中,诱变育种以其技术设备简单、省时省力等优点得到了微生物育种工作者的青睐,在诱变育种技术上取得了巨大进展,为抗生素工业化生产发挥了重要作用。综述了抗生素产生菌的诱变育种研究进展。     

Mutation breeding of Emericella foeniculicola TR21 for improved production of tanshinone IIA

TR21, an original tanshinone IIA-producing endophytic fungus from the root of Salvia miltiorrhiza Bunge, produces low levels of tanshinone IIA. Three techniques were used to rapidly improve tanshinone IIA production: TR21 mutation by ultraviolet radiation (UV), TR21 mutation by sodium nitrite (NaNO₂) and TR21 mutation by a combination of both UV and NaNO₂. An improved mutant, labeled as NU152, was obtained from the combination of UV and NaNO₂. The content of tanshinone IIA produced by NU152 held a relative high value of 51.44 ± 0.22 μg per g, and the NU152 produced a more than 1.46-fold increase in tanshinone IIA yield, compared with the wild type TR21 (P < 0.05). The fungus NU152 showed a possible way for the sustainable production of tanshinone IIA.     

External phosphorus requirements of five tropical grain legumes grown in flowing-solution culture

Summary Five tropical grain legume species were grown for periods from 4 to 20 days in flowing-solution culture at 7 maintained phosphorus (P) concentrations, ranging from 0.25 μM to 16 μM. Critical external P requirements were 0.8 μM for cowpea cv. Vita 4 and soybean cv. Fitzroy, 1.0 μM for pigeon pea cv. Royes, 2.0 μM for mungbean cv. Regur and 3.0 μM for guar cv. Brooks. Plant responses to P deficiency included reduced growth rate, increased root percentage, and increased P uptake potential. The long-term P uptake rates of guar plants were lower than those of the other species at each external P concentration. Guar plants had a low P uptake potential as indicated by short-term^32CP-labelled uptake rate studies from 15 μM P solutions. Cowpea by contrast had high short-term uptake rates indicating a high P uptake potential.     

Symbiotic effectiveness of Bradyrhizobium strains isolated from Parasponia and tropical legumes on Parasponia host species

The symbiotic effectiveness of Bradyrhizobium strains isolated from three species of Parasponia and from legumes were compared on Parasponia grown in Leonard-jars. Effectiveness of each symbiotic association was estimated from dry weight and total nitrogen of shoots and nodules of plants grown on medium free of combined nitrogen. Twenty strains isolated from three species of Parasponia were found to vary in their effectiveness on P. andersonii, the least effective fixing one fifth of the nitrogen of the most effective strains. The outcome of the symbiosis was not associated with the host source of the test strain. P. andersonii, P. rugosa and P. rigida responded differently to a selection of seven strains of Parasponia Bradyrhizobium; some strains were either ineffective or fully effective on each host, while others varied in their symbiotic performance. P. andersonii fixed significantly (P < 0.001) larger quantities of nitrogen than either P. rugosa or P. rigida with p. rigida being the least effective. In contrast to Bradyrhizobium strains from Parasponia spp. which formed nodules rapidly (within 11–20 days), nine strains isolated from legumes required between 25 and 74 days to form partially effective nodules. The thre Parasponia species formed relatively large quantities of nodule tissue relative to the amount of nitrogen fixed and shoot dry matter produced. The Bradyrhizobium isolated from Parasponia plants growing in Papua New Guinea soils could be grouped together on the basis of their infection characteristics on Parasponia and legumes.     

诱变技术在植物育种中的研究新进展

结合近年来国内外对诱变技术的研究进展 ,综述了主要诱变技术的诱变机理及其在植物育种中的应用 ,并讨论了突变体的选择和鉴定技术等问题     

Biomass and density responses in tallgrass prairie legumes to annual fire and topographic position

Annually burned tallgrass prairie is purported to be a nitrogen-limited system, especially when compared to unburned prairie. To test the hypothesis that legumes, potential nitrogen-fixers, would increase in relative abundance in annually burned sites, we assessed their density and biomass for two seasons on upland and lowland soils in annually burned and unburned watersheds. Total legume density was significantly higher in burned (8.0 ± 1.0 [SE] stems/m²) than in unburned watersheds (3.0 ± 0.3 stems/m²). Species with higher (P < 0.05) densities in burned than in unburned prairie included Amorpha canescens, Dalea candida, Dalea purpurea, Lespedeza violacea, Psoralea tenuiflora, and Schrankia nuttallii. Desmodium illinoense was the only legume that responded negatively to annual fire. Total legume biomass did not differ between burned (11.3 ± 1.3 g/m²) and unburned prairie (10.5 ± 0.9 g/m²). Biomass productions of Dalea candida and Psoralea tenuiflora were higher (P < 0.05) in burned than in unburned sites, but biomasses of other legumes were similar between burn treatments. Average individual stem masses of Amorpha canescens and Baptisia bracteata were significantly greater in unburned than in burned prairie. Legumes were affected differentially by topographic location. Total legume density was higher (P < 0.05) on lowland soils (6.6 ± 1.0 stems/m²) than on upland soils (4.3 ± 0.5 stems/m²). However, total legume biomass was not different between lowland soils (12.0 ± 1.2 g/m²) and upland soils (9.9 ± 1.0 g/m²). Densities and biomasses of Amorpha canescens, Desmodium illinoense, and Lespedeza capitata were higher on lowland sites than on upland sites, whereas densities and biomasses of Baptisia bracteata and Dalea purpurea were higher on upland than on lowland soils. Most legume species are either fire tolerant or exhibit a positive response to fire and their persistence in annually burned prairie suggests that they may play an important role in the nitrogen budget of this ecosystem.     

离子束诱变育种研究及应用进展

阐述了离子束诱变的生物效应,研究中有待解决的问题,介绍了离子束诱变在农业、工业育种上的研究进展及成果,并展望了今后的研究前景。     

灵芝菌诱变育种与深层培养的研究

采用紫外线对灵芝菌进行了诱变处理,选育到一株高产菌株ＵＶ－６０Ｓ,其菌体干重达１３．１ｇ／Ｌ,粗多糖含量为６４０ｍｇ／Ｌ,分别比原菌株提高了２１．３％和３０．６％;并研究了培养基组成和培养条件对菌体生长的影响,优化了深层培养的工艺条件,使菌体产量与胞外多糖含量比优化前分别提高了１５．３％和１８．８％。