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.     

Screening faba beans for resistance to Ascochyta fabae by artificial inoculation of seedlings

Summary A method was developed for screening faba bean seedlings for resistance to Ascochyta fabae. Several factors were investigated, including amount and concentration of inoculum, period of high humidity and age of leaves. Seedlings of different cultivars were tested and results compared with available field data. Older leaves proved to be less susceptible than younger leaves. Seedling tests reflected differences in resistance in the field, especially in material uniform in growth habit.     

Identification of segregation-distortion-neutral alleles to improve pollen fertility of indica-japonica hybrids in rice (Oryza sativa L.)

The genetics of resistance to Ascochyta blight (Ascochyta fabae f. sp. fabae) was studied in two populations of faba bean (Vicia faba). Plants of a resistant population, ILB 752, and a susceptible one, NEB 463, were screened for their reaction to the pathogen and the results were quantified on a scale of 0–5. Crosses were made between plants both within and between accessions and the F₁ and F₂ generations assessed in a field trial 21 and 45 days after inoculation. Disease scores were greater at 45 days than at 21 days and they were not significantly affected by the presence of susceptible spreader rows in part of the trial. ILB 752 carried a major dominant gene conferring resistance while NEB 463 carried the recessive allele for susceptibility. Furthermore, a minority of plants of NEB 463 appeared to carry at least one pair of complementary recessive genes, also conferring resistance. Most of the plants of ILB 752 were homozygous for the dominant resistance gene and a few were heterozygous. Reciprocal crosses behaved identically, indicating the absence of maternal effects in the expression of Ascochyta blight resistance in faba beans. The results show that it is important to confirm the level of heterozygosity for the resistance genes in this partially outbreeding species before crossing is commenced. The major dominant gene for resistance, identified in ILB 752, has clear potential for use in breeding for Ascochyta blight resistance. The minor genes identified in NEB 463 also show the potential for accumulating resistance through mass selection. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetics of resistance to 3 isolates of Ascochyta fabae on Faba bean (Vicia faba L.) in controlled conditions

Summary Genetics of resistance to Ascochyta fabae Speg. in Vicia faba L. was studied with a final objective to develop resistant faba bean varieties to Ascochyta blight. The study was conducted separately on 3 single spore isolates (AF10-2 and AF13-2 from Tunisia and AF4-3 from France) and belonging to different groups of virulence (GV1 and GV2). Important general combining ability (GCA) effects were found especially with isolates AF10-2 and AF4-3. Specific combining ability (SCA), although significant for the 3 isolates, was important only with AF13 -2, but less important than GCA. Additive gene effects were predominant to non-additive effects. Lines 29H and A8817 transmitted to their progenies resistance to the 3 isolates, whereas 14–12 and 19TB conferred resistance to their progenies only with isolates AF13-2 and AF4-3, respectively. In the material studied, resistance was generally controlled by dominant genes but also could be attributed to recessive genes although less frequent. Analysis of segregation in the F2 of 2 crosses between the resistant lines (A8817 and 29H) and the susceptible line (14–12) with isolate AF4-3 revealed dominant monogenic control at the level of leaves in the 2 resistant lines and, in addition, a recessive gene controlling resistance of stems. Non-allelic interactions were occasionally manifested and their origin appeared to be due to line 19TB. A recurrent selection scheme was proposed with the objective to develop improved open-pollination populations and synthetic varieties responding to the objective of the national Tunisian research programme on faba bean.     

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.     

Mapping and validation of QTLs for resistance to an Indian isolate of Ascochyta blight pathogen in chickpea

Ascochyta blight (AB) caused by Ascochyta rabiei, is globally the most important foliar disease that limits the productivity of chickpea (Cicer arietinum L.). An intraspecific linkage map of cultivated chickpea was constructed using an F₂ population derived from a cross between an AB susceptible parent ICC 4991 (Pb 7) and an AB resistant parent ICCV 04516. The resultant map consisted of 82 simple sequence repeat (SSR) markers and 2 expressed sequence tag (EST) markers covering 10 linkage groups, spanning a distance of 724.4 cM with an average marker density of 1 marker per 8.6 cM. Three quantitative trait loci (QTLs) were identified that contributed to resistance to an Indian isolate of AB, based on the seedling and adult plant reaction. QTL1 was mapped to LG3 linked to marker TR58 and explained 18.6% of the phenotypic variance (R ²) for AB resistance at the adult plant stage. QTL2 and QTL3 were both mapped to LG4 close to four SSR markers and accounted for 7.7% and 9.3%, respectively, of the total phenotypic variance for AB resistance at seedling stage. The SSR markers which flanked the AB QTLs were validated in a half-sib population derived from the same resistant parent ICCV 04516. Markers TA146 and TR20, linked to QTL2 were shown to be significantly associated with AB resistance at the seedling stage in this half-sib population. The markers linked to these QTLs can be utilized in marker-assisted breeding for AB resistance in chickpea.     

Genetic variability of faba bean genotypes for chocolate spot (<Emphasis Type="Italic">Botrytis fabae</Emphasis>) resistance and yield

Faba bean (Vicia faba L.) has high utility as a food and soil fertility improving crop. One of the major fungal pathogens of faba bean is Botrytis fabae, the causative agent of chocolate spot. The disease affects significantly the leaf, stem, pod and seed of faba bean compromise its productivity in the smallholder farming sector. Nonetheless, there are limited resistant/tolerant faba bean varieties available and disease control technology options. Therefore, it was prudent to evaluate faba bean landraces for chocolate spot resistance. Fifty landraces together with ten improved varieties were evaluated both in the field and in the greenhouse under natural and artificial inoculation with previously selected aggressive Botrytis fabae isolate (Iso-016) from West Gojjam, in Ethiopia. There were highly significant differences (p?<?0.001) among the landraces for reaction to the disease and agronomic traits. Significant positive correlation was recorded between reaction of genotypes in the field and greenhouse disease data. The overall mean disease epidemics varied from 92.5 to 697.5 for the area under disease progress curve (AUDPC). The highest level of resistance was found in the ICARDA lines, ILB-4726, ILB-938 and BPL-710. Of all 18 landrace collections displayed significantly lower disease reaction than the susceptible check. However the resistance was moderate. The selected eighteen landraces will be recommended for use in breeding for chocolate resistance. Overall, resistance was highly heritable, suggesting that phenotypic selection can be exploited to improve chocolate spot resistance in faba bean varieties.     

Quantitative trait loci for temperature-sensitive resistance to <Emphasis Type="Italic">Puccinia striiformis</Emphasis> f. sp. <Emphasis Type="Italic">tritici</Emphasis> in wheat cultivar Flinor

Stripe (yellow) rust, caused by Puccinia striiformis Westend. f. sp. tritici Eriks. (Pst), is an important disease of wheat (Triticum aestivum L.) globally. Use of host resistance is an important strategy to manage the disease. The cultivar Flinor has temperature-sensitive resistance to stripe rust. To map quantitative trait loci (QTLs) for these temperature-sensitive resistances, Flinor was crossed with susceptible cultivar Ming Xian 169. The seedlings of the parents, and F₁, F₃ progeny were screened against Chinese yellow rust race CYR32 in controlled-temperature growth chambers under different temperature regimes. Genetic analysis confirmed two genes for temperature-sensitive stripe rust resistance. A linkage map of SSR markers was constructed using 130 F₃ families derived from the cross. Two temperature-sensitive resistance QTLs were detected on chromosome 5B, designated QYr-tem-5B.1 and QYr-tem-5B.2, respectively, and are separated by a genetic distance of over 50 cM. The loci contributed 33.12 and 37.33% of the total phenotypic variation for infection type, respectively, and up to 70.45% collectively. Favorable alleles of these two QTLs came from Flinor. These two QTLs are temperature-sensitive resistance loci and different from previously reported QTLs for resistance to stripe rust.     

Genetic mapping provides evidence for the role of additive and non-additive QTLs in the response of inter-specific hybrids of <Emphasis Type="Italic">Eucalyptus</Emphasis> to <Emphasis Type="Italic">Puccinia psidii</Emphasis> rust infection

Eucalypts are susceptible to a wide range of diseases. One of the most important diseases that affect Eucalyptus plantations worldwide is caused by the rust fungus Puccinia psidii. Here, we provide evidence on the complex genetic control of rust resistance in Eucalyptus inter-specific hybrids, by analyzing a number of full-sib families that display different patterns of segregation for rust resistance. These families are totally unrelated to those previously used in other inheritance studies of rust resistance. By using a full genome scan with 114 genetic markers (microsatellites and expressed sequence tag derived microsatellites) we also corroborated the existence and segregation of a resistance locus, explaining 11.5% of the phenotypic variation, on linkage group 3, corresponding to Ppr1. This find represents an additional validation of this locus in totally unrelated pedigree. We have also detected significant additive × additive digenic interactions with LOD >10.0 on several linkage groups. The additive and epistatic QTLs identified explain between 29.8 and 44.8% of the phenotypic variability for rust resistance. The recognition that both additive and non-additive genetic variation (epistasis) are important contributors to rust resistance in eucalypts reveals the complexity of this host-pathogen interaction and helps explain the success that breeding has achieved by selecting rust-resistant clones, where all the additive and non-additive effects are readily captured. The positioning of epistatic QTLs also provides starting points to look for the underlying genes or genomic regions controlling this phenotype on the upcoming E. grandis genome sequence.     

小麦慢白粉病QTL对条锈病和叶锈病的兼抗性

聚合兼抗白粉病、条锈病和叶锈病的慢病性基因,是培育持久多抗小麦品种的重要措施。百农64和鲁麦21均为慢白粉病品种,分别含有4个和3个慢白粉病抗性QTL。将百农64与鲁麦21杂交,获得21个聚合2~5个慢白粉病抗性QTL的F₆株系,于2012-2013年度分别在四川郫县和甘肃天水进行条锈病田间抗性鉴定,在河北保定和河南周口进行叶锈病田间抗性鉴定。分析21个株系条锈和叶锈病的最大严重度和病程曲线下面积,检测单个QTL和QTL聚合体对条锈病和叶锈病的抗性效应。结果表明,QPm.caas-4DL、QPm.caas-6BS和QPm.caas-2BL对条锈病均有显著的抗性,分别解释表型变异的16.9%、14.1%和17.3%;QPm.caas-4DL对叶锈病也有显著抗性,可解释表型变异的35.3%;QPm.caas-1A/QPm.caas-4DL/ QPm.caas-2DL/QPm.caas-2BS/QPm.caas-2BL和QPm.caas-1A/QPm.caas-4DL/QPm.caas-2BS/QPm.caas-2BL聚合体对条锈病和叶锈病的抗性显著高于两亲本,它们均含有来自百农64的QPm.caas-4DL以及来自鲁麦21的QPm.caas-2BL和QPm.caas-2BS,表明这些QTL具有明显的兼抗性效应。在小麦抗病育种中,聚合慢病性QTL越多,慢病性越强,聚合4~5个慢病性QTL时,株系可达到高抗甚至接近免疫的水平,是选育持久抗性小麦品种的重要手段。     

Identification of quantitative trait loci associated with resistance to foliar diseases in sorghum [<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench]

Forage sorghum cultivars grown in India are susceptible to various foliar diseases, of which anthracnose, rust, zonate leaf spot, drechslera leaf blight and target leaf spot cause severe damage. We report here the quantitative trait loci (QTLs) conferring resistance to these foliar diseases. QTL analysis was undertaken using 168 F₇ recombinant inbred lines (RILs) of a cross between a female parental line 296B (resistant) and a germplasm accession IS18551 (susceptible). RILs and parents were evaluated in replicated field trials in two environments. A total of twelve QTLs for five foliar diseases on three sorghum linkage groups (SBI-03, SBI-04 and SBI-06) were detected, accounting for 6.9–44.9% phenotypic variance. The morphological marker Plant color (Plcor) was associated with most of the QTL across years and locations. The QTL information generated in this study will aid in the transfer of foliar disease resistance into elite susceptible sorghum breeding lines through marker-assisted selection.     

Inheritance and QTL mapping of leaf rust resistance in the European winter wheat cultivar ‘Beaver’

Genetic studies were conducted on an European winter wheat cultivar, Beaver, to determine the mode of inheritance of leaf rust resistance at seedling and adult plant growth stages using a recombinant doubled haploid population, Beaver/Soissons. Greenhouse studies indicated the involvement of genes Lr13 and Lr26 in governing leaf rust resistance at seedling growth stages, whereas, adult plant resistance (APR) in the field with pathotypes carrying virulence individually for Lr13 and Lr26 showed trigenic inheritance for the population. Marker regression analysis of adult plant field data indicated the involvement of six significant QTLs (chromosomes 1B, 3B, 3D, 4B, 4D and 5A) in year 2005, four QTLs (1B, 3B, 4B and 5A) in 2006, and six QTLs (1A, 1B, 3B, 4A, 4B and 5A) in 2007 for reducing leaf rust severity. QTLs on chromosomes 1B, 4B and 5A were considered the most important because of their detection across years, whereas QTLs on chromosomes 1A, 3B, 3D and 4A were either inconsistent or non-significant and unexplained. Based on an association of closely linked markers with phenotypic data, putative single gene stocks were identified for each consistent QTL and crossing was initiated to develop populations segregating for each to permit fine mapping of the identified regions.     

Screening techniques and sources of resistance to foliar diseases caused by major necrotrophic fungi in grain legumes

Summary Necrotrophic pathogens of the cool season food legumes (pea, lentil, chickpea, faba bean and lupin) cause wide spread disease and severe crop losses throughout the world. Environmental conditions play an important role in the development and spread of these diseases. Form of inoculum, inoculum concentration and physiological plant growth stage all affect the degree of infection and the amount of crop loss. Measures to control these diseases have relied on identification of resistant germplasm and development of resistant varieties through screening in the field and in controlled environments. Procedures for screening and scoring germplasm and breeding lines for resistance have lacked uniformity among the various programs worldwide. However, this review highlights the most consistent screening and scoring procedures that are simple to use and provide reliable results. Sources of resistance to the major necrotrophic fungi are summarized for each of the cool season food legumes. Marker-assisted selection is underway for Ascochyta blight of pea, lentil and chickpea, and Phomopsis blight of lupin. Other measures such as fungicidal control and cultural control are also reviewed. The emerging genomic information on the model legume, Medicago truncatula, which has various degrees of genetic synteny with the cool season food legumes, has promise for identification of closely linked markers for resistance genes and possibly for eventual map-based cloning of resistance genes. Durable resistance to the necrotrophic pathogens is a common goal of cool season food legume breeders.     

Mapping a major gene for growth habit and QTLs for ascochyta blight resistance and flowering time in a population between chickpea and <Emphasis Type="Italic">Cicer reticulatum</Emphasis>

Ascochyta blight is a devastating disease of chickpea. Breeders have been trying to introduce resistance from wild Cicer into cultivated chickpea, however, the effort is hampered by the frequent genetic drag of undesirable traits. Therefore, this study was aimed to identify potential markers linked to plant growth habit, ascochyta blight resistance and days to flowering for marker-assisted breeding. An interspecific F₂ population between chickpea and C. reticulatum was constructed to develop a genetic linkage map. F₂ plants were cloned through stem cuttings for replicated assessment of ascochyta blight resistance. A closely linked marker (TA34) on linkage group (LG) 3 was identified for plant growth habit explaining 95.2% of the variation. Three quantitative trait loci (QTLs) explaining approximately 49% of the phenotypic variation were found for ascochyta blight resistance on LG 3 and LG 4. Flowering time was controlled by two QTLs on LG3 explaining 90.2% of the variation. Ascochyta blight resistance was negatively correlated with flowering time (r = −0.22, P < 0.001) but not correlated with plant growth habit.     

Quantitative trait loci for leafhopper (Empoasca fabae and Empoasca kraemeri) resistance and seed weight in the common bean

A population of 108 common bean recombinant inbred lines (RILs) (F_5:6‐9), derived from a leafhopper (Empoasca fabae and E. kraemeri)‐susceptible cultivar (‘Berna’) and a leafhopper‐resistant line (EMP 419) was used to identify molecular markers genetically linked to leafhopper resistance and seed weight. Bulked segregant analysis and quantitative trait analysis identified eight markers that were associated with resistance to E. fabae, and four markers that were associated with E. kraemeri resistance. Three markers were associated with resistance to both species. A partial linkage map of the bean genome was constructed. Composite interval mapping identified quantitative trait loci (QTL) for resistance to both leaf hopper species on core‐map linkage groups B1, B3 and B7. QTL for seed weight were found close to the locus controlling testa colour and an α‐phaseolin gene.     

Evaluation of a collection of faba bean (Vicia faba L.) genotypes originating from the Maghreb for resistance to chocolate spot (Botrytis fabae) by assessment in the field and laboratory

Screening of 136 faba bean lines forresistance to chocolate spot caused by thefungus Botrytis fabae was conductedin field conditions with artificialinoculation. Detached leaves of thesegenotypes were also assessed for diseaseseverity after inoculation under controlledconditions with a B. fabaesuspension. The BPL710 and Aguadulcegenotypes were inserted as resistant andsusceptible checks, respectively. Diseasesymptoms were scored visually in bothexperiments. Diameter of lesions andproduction of spores were measured in thedetached leaf assay. The disease scoreindex and diameter of lesions were used tocalculate the area under the diseaseprogress curve (AUDPC) to measure thedisease progress. Significant differenceswere detected among genotypes for reactionto the disease in the field. However, nocomplete resistance was observed. Forhighly susceptible and highly resistantgenotypes, the laboratory assay generallyled to the same result as the field test,nevertheless, for more intermediate levelsthe agreement was weak. On detached leaves,diameter of lesions was significantlycorrelated to the AUDPC of disease scores(r = 0.89) and moderately correlated tosporulation (r = 0.52). The correlationbetween field AUDPC and detached leaf AUDPCof disease scores was low (r = 0.26). A lowcorrelation was also observed between fieldAUDPC and lesion size (r = 0.30) andbetween field AUDPC and sporulation (r =0.32). Among the 136 genotypes evaluated inthis study, nine were convincingly andhighly resistant in both tests. FRYM167 andFRYA58 genotypes were the most resistantwith low AUDPC of disease scores, low AUDPCof lesion diameter and low sporeproduction. These genotypes obviously havepartial resistance.     

Pre and posthaustorial resistance to rusts in <Emphasis Type="Italic">Lathyrus cicera</Emphasis> L.

Lathyrus cicera has a high potential as fodder crop in dry areas, but can in particular environments be damaged by rust. Little is known on the availability of resistance against rust fungi and the underlying mechanisms in L. cicera germplasm. The present study assessed and characterised macro and microscopically the resistance to rust fungi Uromyces pisi and U. viciae-fabae, in a collection of L. cicera accessions. A wide range of disease reaction was found in the germplasm collection against the different rust species. L. cicera accessions were highly resistant to U. viciae-fabae being hypersensitive response the most frequent reaction. On the contrary, most accessions showed a compatible interaction with U. pisi, with varying levels of partial resistance, although cases of hypersensitivity were also identified. Differences on germination, orientated germ tube growth and appressoria differentiation were observed but were in general of marginal importance to explain the resistance to U. pisi among the L. cicera accessions. Resistance was due, to a combination of pre and post-haustorial mechanisms.     

Identification of QTLs for resistance to Fusarium wilt and Ascochyta blight in a recombinant inbred population of chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis> L.)

Fusarium wilt (FW; caused by Fusarium oxysporum f. sp. ciceris) and Ascochyta blight (AB; caused by Ascochyta rabiei) are two major biotic stresses that cause significant yield losses in chickpea (Cicer arietinum L.). In order to identify the genomic regions responsible for resistance to FW and AB, 188 recombinant inbred lines derived from a cross JG 62 × ICCV 05530 were phenotyped for reaction to FW and AB under both controlled environment and field conditions. Significant variation in response to FW and AB was detected at all the locations. A genetic map comprising of 111 markers including 84 simple sequence repeats and 27 single nucleotide polymorphism (SNP) loci spanning 261.60 cM was constructed. Five quantitative trait loci (QTLs) were detected for resistance to FW with phenotypic variance explained from 6.63 to 31.55%. Of the five QTLs, three QTLs including a major QTL on CaLG02 and a minor QTL each on CaLG04 and CaLG06 were identified for resistance to race 1 of FW. For race 3, a major QTL each on CaLG02 and CaLG04 were identified. In the case of AB, one QTL for seedling resistance (SR) against ‘Hisar race’ and a minor QTL each for SR and adult plant resistance against isolate 8 of race 6 (3968) were identified. The QTLs and linked markers identified in this study can be utilized for enhancing the FW and AB resistance in elite cultivars using marker-assisted backcrossing.     

Identification of resistance to Ascochyta fabae in Vicia faba germplasm

A total of 752 faba bean accessions were screened under field conditions for resistance to Ascochyta fabae. Several methods of assessing disease development were compared for evaluating the resistance of these accessions. Thirty‐four accessions displayed low disease severity ratings. In 15 of them, lesions were restricted in size and number, whereas in the remaining 19, lesions were well developed but scarce. These lines could have been discarded if screening had depended only on scales based on lesion type, which shows the need to complement such scores with disease severity or to use a simplified scale that integrates both lesion type and the amount of damage.     

Identification of molecular markers linked with crown rust (Puccinia coronata f. sp. lolii) resistance in perennial ryegrass (Lolium perenne) using AFLP markers and a bulked segregant approach

Crown rust resistance is an important selection criterion in ryegrass breeding. The fungal disease caused by P. coronata causes yield loss and a reduced quality of the fodder crop. Molecular markers were used to unravel the genomic organization of crown rust resistance in a segregating L. perenne population. Two genomic regions involved in crown rust resistance were identified that together explained 35% of the phenotypic variance present. Bulked segregant analysis in combination with AFLP markers was a suitable method to identify DNA markers associated with genomic regions of major effect. One cluster of AFLP markers explained 6.1% of the variance and mapped to linkage group 2, a genomic region known to contain crown rust resistance genes. A second cluster of AFLP markers detected a novel genomic region of major effect that explained 27.7% of the phenotypic variance in crown rust resistance. This cluster was unlinked to the cluster on linkage group 2. Divergent selections performed within the segregating F₁ population on the basis of genotype and phenotype revealed that the markers associated with crown rust resistance identified in this study have potential for marker assisted selection. Selection of plants on the basis of markers was more straightforward than the selection on the basis of phenotype.