Screening techniques and sources of resistance to foliar diseases caused by fungi and bacteria in cool season food legumes

Screening techniques are an important component of the overall strategy of breeding for resistance to diseases in cool season food legumes. Suitable screening methods have been developed for several major foliar diseases of chickpea, pea, faba bean, and lentil, and sources of resistance have been identified. International cooperation plays an important role in promoting research and keeping collections of cultivated species and their wild relatives. New biotechnological approaches are promising for enhancing the practical use of genes for resistance.     

Legume breeding for rust resistance: lessons to learn from the model <Emphasis Type="Italic">Medicago truncatula</Emphasis>

Rusts are major biotic constraints of legumes worldwide. Breeding for rust resistance is regarded as the most cost efficient method for rust control. However, in contrast to common bean for which complete monogenic resistance exists and is efficiently used, most of the rust resistance reactions described so far in cool season food legumes are incomplete and of complex inheritance. Incomplete resistance has been described in faba bean, pea, chickpea and lentil and several of their associated QTLs have been mapped. However, the relatively large distance between the QTLs and their associated molecular markers hampers their efficient use for marker assisted selection. Their large genome size drastically hampers the development of genomic resource and limits the saturation of their genetic maps. The use of model plants such as the model legume Medicago truncatula may circumvent this drawback. The important genetic and genomic resources and tools available for this model legume can considerably speed up the discovery and validation of new genes and QTLs in resistance to legume pathogens. Here, the potential of M. truncatula as a model to study rust resistance in legumes, and to transfer rust resistance genes to cool season grain legumes is reviewed.     

Screening techniques and sources of resistance to root diseases in cool season food legumes

Summary Soil-borne fungal diseases are among the most important factors, limiting the yield of grain legumes in many countries worldwide. Root rot, caused by Aphanomyces euteiches, Rhizoctonia solani, Fusarium solani and wilt, caused by several formae speciales of Fusarium oxysporum are the most destructive soil-borne diseases of pea, chickpea, lentil, fababean and lupin. The most effective control of these diseases is achieved through the use of resistant varieties. In this paper, recent advances in conventional and innovative screening methods for disease resistance are presented. Many grain legume accessions, which are maintained in national and international germplasm collections, have been evaluated for disease resistance and numerous resistant varieties have been released following incorporation of identified resistance genes from these sources. Recent identification of molecular markers tightly linked to resistance genes has greatly enhanced breeding programs by making marker assisted selection (MAS) possible and allowing the development of varieties with multiple disease resistance. Progress in the understanding of the biology of soil-borne fungal pathogens of grain legumes is also reviewed with particular reference to the genetic structure of their populations, diagnosis and host–pathogen interaction.     

Application of biotechnology in breeding lentil for resistance to biotic and abiotic stress

Summary Lentil is a self-pollinating diploid (2n = 14 chromosomes) annual cool season legume crop that is produced throughout the world and is highly valued as a high protein food. Several abiotic stresses are important to lentil yields world wide and include drought, heat, salt susceptibility and iron deficiency. The biotic stresses are numerous and include: susceptibility to Ascochyta blight, caused by Ascochyta lentis; Anthracnose, caused by Colletotrichum truncatum; Fusarium wilt, caused by Fusarium oxysporum; Sclerotinia white mold, caused by Sclerotinia sclerotiorum; rust, caused by Uromyces fabae; and numerous aphid transmitted viruses. Lentil is also highly susceptible to several species of Orabanche prevalent in the Mediterranean region, for which there does not appear to be much resistance in the germplasm. Plant breeders and geneticists have addressed these stresses by identifying resistant/tolerant germplasm, determining the genetics involved and the genetic map positions of the resistant genes. To this end progress has been made in mapping the lentil genome and several genetic maps are available that eventually will lead to the development of a consensus map for lentil. Marker density has been limited in the published genetic maps and there is a distinct lack of co-dominant markers that would facilitate comparisons of the available genetic maps and efficient identification of markers closely linked to genes of interest. Molecular breeding of lentil for disease resistance genes using marker assisted selection, particularly for resistance to Ascochyta blight and Anthracnose, is underway in Australia and Canada and promising results have been obtained. Comparative genomics and synteny analyses with closely related legumes promises to further advance the knowledge of the lentil genome and provide lentil breeders with additional genes and selectable markers for use in marker assisted selection. Genomic tools such as macro and micro arrays, reverse genetics and genetic transformation are emerging technologies that may eventually be available for use in lentil crop improvement.     

Identifying and mapping genes of economic significance

An understanding of the genetic basis of characters of commercial importance is critical if a breeder is attempting to move such characters into breeding material. A number of particularly interesting characters or genes have been identified in cool season food legumes, and in pea many of these have been tagged by molecular markers such as allozyme or DNA polymorphisms. This process of mapping and tagging genes has been greatly accelerated by recent developments in molecular biology. It appears that markers will soon be available for many genes in lentil, faba bean, and chickpea and that genetic knowledge developed in one crop will have significant applications in the other cool season food legumes.     

Screening techniques and sources of resistance to root rots and wilts in cool season food legumes

Soilborne, fungal pathogens of cool season food legumes, including seed and seedling blights, rot rots, and wilts are described. Seed and seedling diseases are caused primarily by Pythium and Rhizoctonia spp. The most important fungi causing root rots include Aphanomyces euteiches, Fusarium solani, Pythium spp., Sclerotium rolfsii, and Macrophomina phaseolina. Wilt is caused primarily by various host-specific forms of Fusarium oxysporum. This paper discusses these diseases and screening procedures that emphasize standardization of inoculum levels, maintenance of virulent pathogen cultures, inoculum growth media, environmental conditions, and host plant age. Sources of resistance to these diseases are discussed.     

Potential for wild species in cool season food legume breeding

Wild species which are crossable to cultivated pea, lentil, and chickpea have been collected and are maintained in major germplasm collections throughout the world. Wild species of Vicia crossable to the cultivated faba bean have not been found. The primary, secondary, and tertiary gene pools of the cool season food legumes represent potential genetic diversity that may eventually be exploited in cultivated types to overcome biotic and abiotic stresses. Technical difficulties in obtaining hybrids beyond those within the primary gene pool is a major obstacle. Reproductive isolation, embryo breakdown, hybrid sterility, and limited genetic recombination are major barriers to greater use of wild germplasm. Conventional crossing has been successful in producing interspecific hybrids in Lens, Cicer and Pisum and those hybrids are being evaluated for desired recombinants. In vitro culture of hybrid embryos has been successful in overcoming barriers to wider crosses in Lens. The successful transfer of genes from wide sources to cultivated types can be assisted by repeated backcrossing and selection designed to leave behind undesired traits while transferring genes of interest. Molecular marker assisted selection may become a valuable tool in the future use of wild species. In general, too little is known about the possible genetic variation available in wild species that could be valuable in developing resistance to biotic and abiotic stresses. Current efforts on the use of wide hybridization in the cool season food legumes are reviewed and discussed.     

Screening techniques and sources of tolerance to salinity and mineral nutrient imbalances in cool season food legumes

A large global land area is affected by saline, alkali (sodic), and acid soil conditions. Cool season food legumes are important crops in many countries with such adverse soils. Tolerant genotypes have been identified in many crops, including legumes. However, very little has been published on selection of tolerant cool season food legume crops. The inadequate knowledge and understanding of the responses of cool season food legume crops to these abiotic stresses, necessitates action by a collaborative network of interdisciplinary teams to make rapid progress in identifying tolerant germplasm and developing cultivars better adapted to unfavorable soil conditions.     

Conservation of microsatellite flanking sequences in different taxa of Leguminosae

To test if locus-specific microsatellite markers designed for one genus are informative when used with related genera, the conservation of microsatellite-flanking intergeneric primer binding sites was tested in the closely related tribes Vicieae and Cicereae, from the subfamily Papilionoideae of the Leguminosae family. A total of 123 sequence-tagged microsatellite sites (STMS) markers derived from chickpea were used to amplify loci in lentil (Lens) and dry pea (Pisum). The percentage of chickpea primer binding sites conserved between the three genera was 54.4%. Hybridisation of 63 selected amplified loci to the digoxigenin-labelled oligonucleotide probe (TAA)₅ showed that 69.8% of loci from dry pea and 66.6% of loci from lentil hybridised to the probe. Sequencing of amplified products from chickpea with the primer Ta176 demonstrated that one amplicon contained a microsatellite, whereas another amplicon amplified with the same particular STMS primer pair did not. Amplicons produced from lentil and pea with this primer pairs did not contain microsatellite sequences. Results obtained with Tr7, which amplified a PCR product in lentil and chickpea but not in pea, showed that microsatellite sequences were present in chickpea and absent in lentil. Similar results were obtained with Ts35, which produces amplicons in pea and chickpea; but, again, microsatellite sequences were only present in chickpea. We therefore conclude that STMS derived from chickpea could be used to detect variability between other Leguminosae genera, but it is necessary to verify whether homologous loci are revealed.     

Screening techniques and sources of resistance to abiotic stresses in cool-season food legumes

Summary The adaptability and productivity of cool-season food legumes (chickpea, faba bean, lentil, pea) are limited by major abiotic stresses including drought, heat, frost, chilling, waterlogging, salinity and mineral toxicities. The severity of these stresses is unpredictable in field experiments, so field trials are increasingly supplemented with controlled-environment testing and physiological screening. For drought testing, irrigation is used in dry fields and rain-out shelters in damp ones. Carbon isotope discrimination (Δ¹³C) is a well-established screen for drought tolerance in C3 cereal crops which is now being validated for use in grain legumes, but it is relatively expensive per sample and more economical methods include stomatal conductance and canopy temperature. Chickpea lines ICC4958 and FLIP87-59C and faba bean line ILB938 have demonstrated good drought tolerance parameters in different experiments. For frost tolerance, an efficient controlled-environment procedure involves exposing hardened pot-grown plants to sub-zero temperatures. Faba beans Cote d’Or and BPL4628 as well as lentil ILL5865 have demonstrated good freezing tolerance in such tests. Chilling-tolerance tests are more commonly conducted in the field and lentil line ILL1878 as well as derivatives of interspecific crosses between chickpea and its wild relatives have repeatedly shown good results. The timing of chilling is particularly important as temperatures which are not lethal to the plant can greatly disrupt fertilization of flowers. Salinity response can be determined using hydroponic methods with a sand or gravel substrate and rapid, efficient scoring is based on leaf symptoms. Many lines of chickpea, faba bean and lentil have shown good salinity tolerance in a single article but none has become a benchmark. Waterlogging tolerance can be evaluated using paired hydroponic systems, one oxygenated and the other de-oxygenated. The development of lysigenous cavities or aerenchyma in roots, common in warm-season legumes, is reported in pea and lentil but is not well established in chickpea or faba bean. Many stresses are associated with oxidative damage leading to changes in chlorophyll fluorescence, membrane stability and peroxidase levels. An additional factor relevant to the legumes is the response of the symbiotic nitrogen-fixing bacteria to the stress.     

Screening techniques and sources of resistance to rusts and mildews in grain legumes

Summary In this paper we review the existence of sources of resistance and the various available screening methods for resistance in grain legumes against the airborne pathogens powdery mildews, downy mildews and rusts. Available resistance against these pathogens is not abundant and is particularly in risk of erosion owing to the constant generation and introduction of new races of the pathogen. A continuous search for more resistance sources is therefore a priority in legume breeding and special emphasis should be paid to selection of resistance mechanisms that are likely to be durable and to implementation of strategies to prolong the durability of existing resistance.     

Water relations, gas exchange and growth of cool-season grain legumes in a Mediterranean-type environment

The aim of this study was to identify the physiological characteristics which may affect the yield of six cool-season grain legume species grown in a water-limited Mediterranean-type climate in Western Australia. The rate of net photosynthesis, stomatal conductance and water relations were measured from flowering to complete leaf senescence in white lupin, chickpea, faba bean, field pea, grass pea and lentil. In irrigated plants, the midday leaf water potential was about −0.6 MPa in all species, while the maximum rate of leaf photosynthesis was 30 μmol m⁻² s⁻¹ for chickpea and white lupin, and below 20 μmol m⁻² s⁻¹ for the other species. With the development of water deficits, the leaf water potential in rain-fed plants decreased to about −3 MPa in chickpea and lentil and −2 MPa in the other species. Photosynthesis and stomatal conductance decreased markedly as the leaf water potential decreased below −0.9 MPa in all six species, including chickpea and lentil, which showed a high degree of osmotic adjustment. Despite the similarity in water use, restricted to the top 40 cm of soil, and water relations characteristics, yields varied markedly among species. Yields were strongly correlated with early biomass production and early pod development.     

Lathyrus improvement for resistance against biotic and abiotic stresses: From classical breeding to marker assisted selection

Summary Several Lathyrus species and in particular Lathyrus sativus (grass pea) have great agronomic potential as grain and forage legume, especially in drought conditions. Grass pea is rightly considered as one of the most promising sources of calories and protein for the vast and expanding populations of drought-prone and marginal areas of Asia and Africa. It is virtually the only species that can yield high protein food and feed under these conditions. It is superior in yield, protein value, nitrogen fixation, and drought, flood and salinity tolerance than other legume crops. Lathyrus species have a considerable potential in crop rotation, improving soil physical conditions; reducing the amount of disease and weed populations, with the overall reduction of production costs. Grass pea was already in use in Neolithic times, and presently is considered as a model crop for sustainable agriculture. As a result of the little breeding effort invested in it compared to other legumes, grass pea cultivation has shown a regressive pattern in many areas in recent decades. This is due to variable yield caused by sensitivity to diseases and stress factors and above all, to the presence of the neurotoxin β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP), increasing the danger of genetic erosion. However, both L. sativus and L. cicera are gaining interest as grain legume crops in Mediterranean-type environments and production is increasing in Ethiopia, China, Australia and several European countries. This paper reviews research work on Lathyrus breeding focusing mainly on biotic and abiotic resistance improvement, and lists current developments in biotechnologies to identify challenges for Lathyrus improvement in the future.     

Inheritance of resistance to pea blight (Ascochyta pinodella) and induction of resistance in pea (Pisum sativum L.)

Summary Pea blight caused by Assochyta pinodella does considerable damage to the pea crop every year. To ascertain the inheritance of resistance to pea blight and incorporate resistance in the commercial cultivars, crosses were made between Kinnauri resistant to pea blight and four highly susceptible commercial pea cultivars — Bonneville, Lincoln, GC 141 and Sel. 18. Studies of the F₁'s, F₂'s, back crosses and F₃'s indicated that Kinnauri carries a dominant gene imparting resistance to pea blight.     

Water use and water use efficiency of cool season grain legumes in low rainfall Mediterranean-type environments

The water use (E_t) and water use efficiency (WUE) of a range of cool season grain legume species (field pea [Pisum sativum L.], faba bean [Vicia faba L.], chickpea [Cicer arietinum L.], lentil [Lens culinaris Med.], albus lupin [Lupinus albus L.], dwarf chickling [Lathyrus cicera L.], ochrus chickling [Lathyrus ochrus L.], grass pea [Lathyrus sativus L.], narbon bean [Vicia narbonensis L.], common vetch [Vicia sativa L.], and purple vetch [Vicia benghalensis L.]) were examined on fine textured neutral to alkaline soils in the low to medium rainfall Mediterranean-type environments in south-western Australia at Merredin and Mullewa in two seasons. There was no difference in the total E_t between grain legumes at either site in either year. There was also no variation in soil water extraction between species on the shallow sandy loam soil at Merredin. However, C. arietinum, L. sativus and L. cicera had greater water extraction and P. sativum the least water extraction at Mullewa where soil conditions were less hostile and root penetration was not restricted. The pattern of water use varied markedly between the grain legume species examined. Grain yield was positively correlated with post-flowering water use (E_tpa) in both erect (r=0.59) and prostrate (r=0.54) grain legume species. Water use efficiencies for dry matter production (WUE_dm) of up to 30 kg ha⁻¹ mm⁻¹ for V. faba and V. narbonensis at Merredin, and water use efficiencies for grain yield (WUE_gr) of up to 16 kg ha⁻¹ mm⁻¹ for P. sativum and 13 kg ha⁻¹ mm⁻¹ for V. faba at Mullewa, were comparable to those reported for cereals and other grain legumes in previous studies in this and other environments. Potential transpiration efficiencies (TE) of 15 kg ha⁻¹ mm⁻¹ together with soil evaporation (E_s) values of 100–125 mm were estimated in this and associated studies, and can be used as benchmark values to assess the yield potential of cool season grain legume crops in low rainfall Mediterranean-type environments. The major traits of adaptation for grain legume species producing large yields in this short season environment are early flowering, and pod and seed set before the onset of terminal drought. Early phenology together with rapid ground cover and dry matter production allows greater water use in the post flowering period. This leads to greater partitioning of dry matter into seed, which is reflected in greater harvest index (HI) and WUE_gr, as was observed for V. faba and P. sativum. Improvement in the adaptation of other grain legume species to short season Mediterranean-type environments requires increased early growth for rapid ground cover and improved tolerance to low temperatures (especially for C. arietinum) during flowering and podding.     

Methods for screening resistance in chickpea to Ascochyta blight

Summary In Morocco, Ascochyta blight is a major limiting factor in chickpea production. The best long term solution to the problem seems to be the production of chickpea lines with durable resistance to the disease. Because of the nature of durable resistance, screening methods assessing resistance quantitatively had to be developed. Four methods are described: a seedling test, a germination test, a score of the percentage infected pods and a hair density score. With these screening methods a quantitative assessment of resistance in chickpea to blight appeared possible.Mr Pieters is with the FAO Plant Protection and Production division. Mr Tahiri is with the Service de Contrôle des Semences et Plants in Morocco.     

Transfer of the Kosena Rfk1 gene,required in hybrid seed production,from oilseed rape to turnip rape

Radiant frost is a major abiotic stress, and one of the principal limiting factors for agricultural production worldwide, including Australia. Legumes, including field pea, faba bean, lentil and chickpea, are very sensitive to chilling and freezing temperatures, particularly at the flowering, early pod formation and seed filling stages. Radiant frost events occur when plants and soil absorb the sunlight during the day time and radiate heat during the night when the sky is clear and the air is still. Dense chilled air settles into the lowest areas of the canopy, where the most serious frost damage occurs. The cold air causes nucleation of the intracellular fluid in plant tissues and the subsequent rupturing of the plasma membrane. Among the cool season grain legume crops, chickpea, lentil and faba bean and field pea are the most susceptible to radiant frost injury during the reproductive stages. The more sensitive stages are flowering and podding. Frost at the reproductive stage results in flower abortion, poor pod set and impaired pod filling, leading to a drastic reduction in yield and quality. In contrast, in the UK and European countries, frost stress is related to the vegetative stages and, in particular, the effects of frost have been studied on cotyledon, uni/tri-foliolate leaf and seedling stages during the first few weeks of growth. Few winter genotypes have been identified as frost tolerant at vegetative stages. Vegetative frost tolerance is not related to reproductive frost tolerance, and hybrids from the vegetative frost-tolerant genotypes may not necessarily be tolerant at the reproductive stage. Tolerance to radiant frost has an inverse relationship with plant age. In the field, frost tolerance decreases from the vegetative stage to reproductive stage. Unlike wheat and barley, it is difficult to analyse and score frost damage in grain legume crops due to the presence of various phenophases on one plant at the reproductive stage. The extent of frost damage depends on the specific phenophases on a particular plant. However, current studies on genetic transformation of cold tolerant gene(s), membrane modifications, anti-freeze substances and ice nucleating or inhibiting agents provide useful information to improve our current understanding on frost damage and related mechanisms. The effects of frost damage on yield and grain quality illustrate the significance of this area of research. This review discusses the problem of radiant frost damage to cool season legumes in Australia and the associated research that has been carried out to combat this problem locally and worldwide. The available literature varies between species, specific climatic conditions and origin.     

Chickpea molecular breeding: New tools and concepts

Summary Chickpea is a cool season grain legume of exceptionally high nutritive value and most versatile food use. It is mostly grown under rain fed conditions in arid and semi-arid areas around the world. Despite growing demand and high yield potential, chickpea yield is unstable and productivity is stagnant at unacceptably low levels. Major yield increases could be achieved by development and use of cultivars that resist/tolerate abiotic and biotic stresses. In recent years the wide use of early maturing cultivars that escape drought stress led to significant increases in chickpea productivity. In the Mediterranean region, yield could be increased by shifting the sowing date from spring to winter. However, this is hampered by the sensitivity of the crop to low temperatures and the fungal pathogen Ascochyta rabiei. Drought, pod borer (Helicoverpa spp.) and the fungus Fusarium oxysporum additionally reduce harvests there and in other parts of the world. Tolerance to rising salinity will be a future advantage in many regions. Therefore, chickpea breeding focuses on increasing yield by pyramiding genes for resistance/tolerance to the fungi, to pod borer, salinity, cold and drought into elite germplasm. Progress in breeding necessitates a better understanding of the genetics underlying these traits. Marker-assisted selection (MAS) would allow a better targeting of the desired genes. Genetic mapping in chickpea, for a long time hampered by the little variability in chickpea’s genome, is today facilitated by highly polymorphic, co-dominant microsatellite-based markers. Their application for the genetic mapping of traits led to inter-laboratory comparable maps. This paper reviews the current situation of chickpea genome mapping, tagging of genes for ascochyta blight, fusarium wilt resistance and other traits, and requirements for MAS. Conventional breeding strategies to tolerate/avoid drought and chilling effects at flowering time, essential for changing from spring to winter sowing, are described. Recent approaches and future prospects for functional genomics of chickpea are discussed.     

Field performance of natural narrow-leafed lupin from the northwestern Spain

Summary Narrow-leafed lupin or lupine (Lupinus angustifolius L.) is one of the three species of the genus Lupinus that grows naturally in Galicia (northwestern Spain). In this region, with more than one million of cattle heads, almost 20% of Spanish total, there is no cultivation of any protein legume for feed. Lupins are widely used as a source of protein and energy in livestock feed and would contribute to the supply of vegetable protein at low cost. A 2-year study of natural narrow-leafed lupin germplasm was conducted under winter Mediterranean conditions in northwestern Spain. Fifty-nine wild populations and two cultivars developed in Poland were evaluated for major morphological, phenological, and agronomical characteristics. The objectives were to assess the agronomic potential of this germplasm for the future production and breeding, and to know the relationships among populations studied. Lupin populations showed significant differences for most of the traits studied. Genotype × environment interaction was significant for plant height, green and dry mass, pod length, seeds per pod, seed length and width, and water permeability of seed coat, indicating that some genotypes were better fitted to a specific environment than others. Three narrow-leafed lupin populations (LUP-0098, LUP-0138 and LUP-0200) were identified with suitable agronomical characteristics for their possible future cultivation in the region and breeding purposes. The accession LUP-0138 presented the best behaviour for seed production. These results open the way for the winter narrow-leafed lupin to become a promising crop in the future for the northwestern Spain.     

Current and future strategies in breeding lentil for resistance to biotic and abiotic stresses

Lentil production is limited by lack of moisture and unfavorable temperatures throughout its distribution. Waterlogging and salinity are only locally important. Progress has been made in breeding for tolerance to drought through selection for an appropriate phenology and increased water use efficiency and in breeding for winter hardiness through selection for cold tolerance.The diseases rust, vascular wilt, and Ascochyta blight, caused by Uromyces viciae-fabae, Fusarium oxysporum f. sp. lentis, and Ascochyta fabae f. sp. lentis, respectively, are the key fungal pathogens of lentil. Cultivars with resistance to rust and Ascochyta blight have been released in several countries and resistant sources to vascular wilt are being exploited. Sources of resistance to several other fungal and viral diseases of regional importance are known. In contrast, although the pea leaf weevil (Sitona spp.) and the parasitic weed broomrape (Orobanche spp.), and to a lesser extent the cyst nematode (Heterodera ciceri), are significant yield reducers of lentil, no sources of resistance to these biotic stresses have been found. Directions for future research in lentil on both biotic and abiotic stresses are discussed.