Mutations affecting nodulation in grain legumes and their potential in sustainable cropping systems

Many spontaneous and a large number of induced mutants that show altered nodulation pattern have been isolated in pea, soybean, common bean, faba bean, chickpea, groundnut and pigeonpea. Available information on nodulation mutants in these crops is summarised. The importance of nodulation mutants in basic studies on plant-microbe symbiotic interactions, nitrogen fixation and breeding of cultivars with higher yield and nitrogen fixation rate are examined. The nodulation mutants, after inoculation with specific bacterial strains or a number of different strains, show either: no nodulation (nod-), few nodules (nod+/-), ineffective nodulation (fix-), hyper nodulation (nod++) or hypernodulation even in the presence of otherwise inhibitory nitrate levels (nts). No spontaneous hypernodulation or nts mutants have been found, all have been induced in independent experiments using different cultivars of pea, soybean and common bean after mutagenising seeds. Most nodulation mutants show monogenic recessive inheritance, though semi-dominant and dominant inheritance is also reported. Nodule number is controlled by a process known as autoregulation; hypernodulating mutants show relaxed autoregulation. By grafting shoots of hypernodulating soybean mutant on normal nodulating soybean, mungbean and hyacinth bean, presence of a common, translocatable signal has been shown. Nodulation mutants have contributed to the understanding of the genetic regulation of host-symbiont interactions, nodule development and N fixation. Initially, the hypernodulating mutants were found to be poor in yield. Using the induced hypernodulating mutant, a new soybean cultivar ‘Nitrobean 60’, has been released in Australia. This cultivar is reported to have given 15% higher yield over cv. ‘Bragg,’ and contributed a higher amount of fixed N to the following cereal crop in rotation. Prospects of using the nodulation mutants in developing grain legume cultivars that combine high yield with high residual N, within the bioenergetic constraints, for developing sustainable cropping systems are examined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Contents Volume 131 2003

Volume Contents

Contents Volume 131 2003     

Shoot Regeneration from Anther Culture of Sunflower (Helianthus annuus) and Some Interspecific Hybrids as Affected by Genotype and Culture Procedure

Anther culture has been demonstrated to be an applicable technique for the development of doubled haploid, i. e. homozygous lines of many crop species. In some species, androgenetic doubled haploids have already been shown to be a useful tool for breeding. However, anther culture results in sunflower have been rather unsatisfactory up to now. As in other species, anther culture response of sunflower (Helianthus sp.) is strongly affected by physical, nutritional, physiological and genetical factors. By testing a number of different culture parameters, i. e. donor plant stages, culture media and conditions, and appropriate schedule could be worked out for the successful regeneration of shoots – at least for a number of sunflower lines and interspecific hybrids.     

Genotypic and exogenous factors affecting shoot regeneration from anther callus of linseed (Linum usitatissimum L.)

Summary The objective of this study was to investigate factors affecting the regeneration capacity of linseed anther culture. Four different environmental conditions in a phytotron were tested with regard to their effects on anther donor plants of cv. Hella. Anther response and shoot regeneration from anther callus was maximal when donor plants were grown in a 16 hrs-day at 14°C day/8°C night temperature. Anthers of four linseed genotypes were cultured on different media. Maximum shoot regeneration was achieved when the induced calli were transferred onto a modified N6 medium containing zeatin (1 mg l^-1). Most of the calli regenerated shoots in the second subculture on regeneration media. Shoots were rooted on modified B5 or MS media containing NAA (0.1 mg l^-1). Cytological examinations of incubated anthers and root tips of regenerated plants indicated that the anther calli were derived from microspores.Abbreviations B5 Gamborg's (1975) medium - BAP 6-benzylaminopurine - 2,4D dichlorophenoxyacetic acid - N6 Chu's (1978) medium - NAA -naphthaleneacetic acid - MS Murashige & Skoog's (1962) medium - ZEA zeatin     

Breeding for Modified Fatty Acid Composition by Induced Mutations in Linseed (Linum usitatissimum L.)

Seeds of linseed (Linum usitatissimum L.) cultivars ‘Raulinus’ and ‘Bionda’ were treated mutagenically with ethyl methanesulfonate (EMS) in order to broaden the variation of fatty acid composition in the seed oil and to select mutants with reduced linolenic acid (C18: 3) content. The M₂ generation was evaluated for fatty acid composition of the oil. Genetic variation for unsaturated fatty acids was demonstrated to be extended in the M₂ generation as compared to the controls. Finally in the M₅ generation of cv. ‘Raulinus’, lines with reduced C18:3 (< 40% vs. 55%) and correspondingly increased linoleic or oleic acid contents, respectively, could be selected. These mutants proved to be genetically stable as demonstrated by parent-offspring (M₄/M₅) regression.     

Global impact of mutation-derived varieties

During the past seventy years, worldwide more than 2250 varieties have been released that have been derived either as direct mutants or from their progenies. Induction of mutations with radiation has been the most frequently used method for directly developed mutant varieties. The prime strategy in mutation-based breeding has been to upgrade the well-adapted plant varieties by altering one or two major traits, which limit their productivity or enhance their quality value. In this paper, the global impact of mutation-derived varieties on food production and quality enhancement is presented. In addition, the economic contribution of the selected mutant varieties of rice, barley, cotton, groundnut, pulses, sunflower, rapeseed and Japanese pear is discussed. In several mutation-derived varieties, the changed traits have resulted in synergistic effect on increasing the yield and quality of the crop, improving agronomic inputs, crop rotation, and consumer acceptance. In contrast to the currently protected plant varieties or germplasm and increasing restrictions on their use, the induced mutants have been freely available for plant breeding. Many mutants have made transnational impact on increasing yield and quality of several seed-propagated crops. Induced mutations will continue to have an increasing role in creating crop varieties with traits such as modified oil, protein and starch quality, enhanced uptake of specific metals, deeper rooting system, and resistance to drought, diseases and salinity as a major component of the environmentally sustainable agriculture. Future research on induced mutations would also be important in the functional genomics of many food crops. This revised version was published online in July 2006 with corrections to the Cover Date.