Variation in the grass pea (Lathyrus sativus L.) and wild species

Summary Forty-nine accessions of Lathyrus sativus were studied for morphological variation. Data were analysed using Principal Components Analysis and Cluster Analysis. The variation in 14 species of Section Lathyrus was also evaluated in order to ascertain affinities between L. sativus and other species. L. sativus is a highly variable species, and there is a clear distinction between the blue-flowered forms from south-west Asia, Ethiopia and the Indian subcontinent, and the white and white and blue flowered forms with white seeds which have a more westerly distribution. Differences in vegetative parts may be due to selection for forage types. L. sativus appears to be closely related to L. cicera and L. gorgoni, and this relationship needs further investigation.     

Molecular marker analysis of genetic variation characterizing a grasspea (Lathyrus sativus) collection from central Italy

Levels of genetic similarity characterizing 20 grasspea (Lathyrus sativus L.) populations collected in central Italy (17 populations in the Marche region and three populations in the Abruzzo region) were analysed with amplified fragment length polymorphism (AFLP) molecular markers. Two main clusters were found: one included large‐seeded populations from farms that were not market‐oriented (named Household populations) and the second, small‐seeded populations, cultivated in market‐oriented farms (named Commercial populations). Relationships among populations collected in different regions were found, although one population of the Abruzzo region was placed between the two main clusters, suggesting a possible further genetic differentiation within this grasspea germplasm collection. Principal component analysis based on AFLP marker frequency was effective in identifying polymorphic markers showing high discriminating ability between clusters H and C. In particular, seven markers showing high positive and three markers with low negative PC1 scores showed an almost cluster‐specific distribution. These results will be useful for enhancing Italian grasspea germplasm use in plant‐breeding programmes and for extending grasspea cultivation within the sustainable agricultural systems of central Italy.     

Collection and evaluation of grasspea (Lathyrus sativus L.) germplasm of central Italy

Characterization of 16 grasspea (Lathyrus sativus L.) accessions collected in central Italy (Marche region) was performed for morphological and agronomic traits and for 3‐(‐N‐oxalyl)‐L‐2,3 diaminoprop‐ionic acid (ODAP) content. Field trials, carried out in two locations, revealed high among‐population genetic variation. In particular, an evident differentiation between commercial populations, cultivated by market‐oriented farms, and household populations (not market‐oriented) was found. Genotype × environment interaction was negligible. Medium‐high values of ODAP content were observed following colorimetric and capillary electrophoresis analyses. A high positive correlation between the two methods was found (r = 0.83**), but the colorimetric values showed, on average, significant 14% lower ODAP values. This research represents a pre‐breeding activity aimed at developing a breeding programme for the preservation and utilization of Italian grasspea germplasm within sustainable or organic agricultural systems.     

Qualitative resistance to powdery mildew in hybrid sweet peas

Lathyrus odoratus L. × Lathyrus belinensis L. hybrids were produced using L. belinensis as the pollen parent, with fertile seed produced by the L. odoratus parent. The F1 hybrid plants were completely self-sterile, but produced viable seeds when backcrossed to L. odoratus. The plants produced by backcrossing resembled L. odoratus, the flower colour being purple/magenta, and were self-fertile. Both hybrid plants and those produced by back crossing to L. odoratus were resistant to Erysiphe pisi DC that causes powdery mildew in sweet peas. Continued backcrossing resulted in hybrid plants, that closely resembled the L. odoratus parent, but segregated for complete resistance/susceptibility to E. pisi,with a ratio of 2.46:1 resistant to sensitive plants. This suggests the presence of a single dominant gene that confers resistance. When resistant and sensitive plants were inoculated with E. pisi and their leaf surfaces examined,using a Scanning Electron Microscope, it was found that although spores germinated on the leaves of both resistant and sensitive plants, spores present on resistant plants collapsed shortly after germination. Possible reasons for this are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of resistance to powdery mildew (Erysiphe pisi) in a germplasm collection of Lathyrus sativus

Lathyrus sativus has a considerable potential for dry land‐farming systems but can be severely damaged by powdery mildew infection. Little is known about the availability of resistance against powdery mildew and the underlying mechanisms in the Lathyrus genus. A range of resistance reactions was identified in a collection of Iberian‐cultivated L. sativus germplasm. In most cases a compatible reaction to powdery mildew with no macroscopically visible necrosis was observed. Nevertheless, accessions with reduced disease severity despite being of a high infection type have been identified. The genes responsible for this partial resistance will be potentially useful for the development of durable resistant cultivars of Lathyrus spp., and may also be of value for the improvement of other related cultivated leguminous plants.     

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.     

Phenotypic polymorphism of six enzymes in the grasspea (Lathyrus sativus L.)

Summary The phenotype variation in six enzymes, 6-phosphogluconate dehydrogenase (6-PGD), malate dehydrogenase (MDH), peroxidase (PRX), isocitrate dehydrogenase (IDH), galactose dehydrogenase (GD) and glutamate oxaloacetate transaminase (GOT), was investigated using horizontal starch gel electrophoresis in 52 accessions of the grasspea, Lathyrus sativus. Phenotypic polymorphism was observed for all six enzymes. High phenotypic polymorphism (Pj) was observed for PRX and 6-PGD, while there was little polymorphism for GOT, with only two accessions showing variation. There was no correlation between phenotypic polymorphism and region of origin, or groupings of accessions made on the basis of flower colour. Tentative genetic interpretations of banding patterns are given for five of the enzyme systems. The level of apparent heterozygosity was higher than expected in this predominantly autogamous species. The level of variation in the grasspea is discussed in terms of its potential for exploitation through plant breeding.     

Genotype-environment interaction for seed yield and ODAP concentration of Lathyrus sativus L. and L. cicera L. in Mediterranean-type environments

In 1994, 407 L. sativus and 96 L. cicera lines were evaluated for phenology, seed yield and seed ODAP (a neurotoxin) concentration in the Mediterranean-type climate of south-western Australia. A selected number of lines from this study were grown at three sites in south-western Australia in 1995 and 1996, to examine genotype-environment interactions on seed yield and ODAP concentration in the seed of the two Lathyrus spp. Principal components analysis showed that L. sativus lines grown in 1995 and 1996 could be divided into two geographical origins: Indian sub-continent and Mediterranean/European. Those lines of Mediterranean/European origin were consistently higher yielding (both in 1994 and 1995/96), with much larger seeds and later phenology. In L. cicera seed yield was closely associated with greater mean seed weight and to a lesser extent with early phenology. The genotype-environment study indicated that higher yielding lines of both species generally responded to favourable environments; in the case of L. sativus the Mediterranean/European lines and for L. cicera the larger seeded, earlier phenology lines. For both species, genotype was the most important determinant of ODAP concentration and environment had less influence. Genotype-environment interactions had no effect on seed ODAP concentrations. In terms of seed yield, both species showed substantial potential in the environments tested. Further improvements in adaptation, seed yield and reduction in ODAP are possible in both species. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of genomic simple sequence repeat markers from an enriched genomic library of grass pea (Lathyrus sativus L.)

Simple sequence repeat (SSR) or microsatellite markers are a valuable tool for several purposes such as evaluation of genetic diversity, fingerprinting, marker‐assisted selection and breeding. In this study, a SSR genomic enriched library was developed in Lathyrus sativus (grass pea) by affinity capture of restriction fragments to biotinylated microsatellite oligonucleotides. About 400 randomly selected clones were sequenced, and SSRs were present in approximately 30% of them. Clones contained 75%, 9% and 16% of simple, interrupted and compound SSRs, respectively. Of the 10 SSRs tested, 7 primer pairs produced clearly distinguishable DNA banding patterns. Successively, SSR primer pairs were successfully tested to reveal polymorphism in a set of four different grass pea germplasm accessions. The transferability of SSR markers was high among three related species of Lathyrus, namely Lathyrus cicera, Lathyrus ochrus and Lathyrus tingitanus, and the legume crop, Pisum sativum. These results indicate that the novel SSR markers are informative and will be useful and convenient for genetic analysis in grass pea and related species.     

Water Deficit during the Reproductive Period of Grass Pea (Lathyrus sativus L.) Reduced Grain Yield but Maintained Seed Size

The grain legume grass pea (Lathyrus sativus L.) is adapted to drought‐prone environments, but the extent and mechanisms of its tolerance are not well understood. In a pot experiment, water deficit was imposed on plants by withholding water from first flowering until predawn leaf water potential (LWP_pd) was ?3.12 MPa. Water deficit reduced dry matter, seed yield, harvest index and water use efficiency by 60 %, 87 %, 67 % and 75 %, respectively, when compared with the controls. Flower production stopped when LWP_pd fell to ?1.8 MPa. At LWP_pd?1.5 MPa, only 25 % of flowers resulted in filled pods (compared with 95 % filled pods in the control) with the rest aborted as flowers (48 %) or pods (27 %). Filled pods had more aborted ovules than controls, resulting in 29 % less seeds per pod. Water deficit reduced pollen viability, germination and the number of pollen tubes reaching the ovary by 13 %, 25 % and 31 %, respectively. Emergence from seeds produced from water‐deficient plants was 21 % less than controls, but seedling shoot dry mass was 18 % higher, in accordance with the 19 % higher seed mass. The sensitivity of flowering to drought limited pod numbers but enabled plants to retain existing pods and develop near‐normal seeds with low β‐N‐oxalyl‐l ‐α‐β‐diaminopropionic acid toxin concentrations. This trait is useful for farming systems reliant on harvested seed for the next crop and in cases where seed size influences the value of the product.     

Current status and future strategy in breeding grasspea (Lathyrus sativus)

Efforts in grasspea (Lathyrus sativus) improvement have increased since the development of lines that are very low in the neurotoxin Beta-N-oxalyl-L-alpha-beta-diamino propionic acid (ODAP); also referred to as Beta-N oxalyl-amino-L-alanine (BOAA). Many programs now address several related aspects of improvement simultaneously. These include reduced ODAP concentrations, insect and disease resistance, nitrogen fixation, agronomic practices, fodder and forage production, and components for increased yielding ability. The coordinated, multidisciplinary approach now being applied to the genetic improvement of grasspea should allow the potential of this largely neglected grain legume to be fully realized.     

Evolving gene pools in crop plants

Summary The three gene pool system can be applied usefully to the whole range of crop plants. The primary gene pool (GP1) show varying degrees of fragmentation. No morphological discontinuity is apparent between wild and cultivated Lathyrus sativus but clear discontinuities have developed between conspecific wild and cultivated Phaseolus and Vigna species. Further discontinuities can develop in cultigens where disruptive selection has been practiced, as in Beta vulgaris, Linum usitatissimum and Brassica oleracea where more than one distinct crop has evolved within a single biological species. Each such crop has developed its own distinctive gene pool.     

Molecular analysis of Lathyrus sativus L. (grasspea) and related Lathyrus species

Eight Lathyrus sativus L. accessions from a variety of geographic origins were used to study intraspecific genetic diversity using RAPD analysis. Fourteen decamer primers produced 64 amplification products, 50% of which were polymorphic between the samples. Jaccard's coefficient of genetic similarity was calculated between samples and a dendrogram was constructed by an unweighted pair-group method with arithmetical averages (UPGMA). The dendrogram showed that most of the L. sativus plants clustered into accessions or common geographical areas. The average genetic similarity coefficient within accessions was 0.12 and between accessions was 0.20, indicating a low level of intraspecific genetic variation. Interspecific genetic diversity and phylogenetic relationships of eight Lathyrus species, including L. sativus and Pisum sativum L. (field pea) were examined using 14 decamer primers which produced 283 amplification products. All amplification products were polymorphic across the nine species. In the dendrogram the Lathyrus species clustered into three distinct groups which correlated with the Sections Lathyrus, Clymenum and Linearicarpus. This supports traditional taxonomic classifications of the genus Lathyrus which are based on morphological traits. Of the species from Section Lathyrus, L. gorgoni and L. cicera were the most similar to L. sativus. The results suggest that a strategy of breeding for producing lines of L. sativus with increased genetic variation would be effectively achieved through hybrid production between accessions from wide geographic areas particularly the Mediterranean area and the Indian subcontinent. However, the most effective method would be introgression of germplasm from other species in Section Lathyrus. This revised version was published online in July 2006 with corrections to the Cover Date.     

Incompatibility in diploid and tetraploid crosses of Cucumis sativus and Cucumis metuliferus

The African horned cucumber (Cucumis metuliferus Naud.; 2x = 2n = 24) contains genes that can confer resistance to many important cucumber (C. sativus L.; 2x = 2n = 14) pests [e.g., root-knotnematode, Meloidogyne incognita (Kofoid & White) Chitwood]. Cucumber is highly susceptible to this root-knot nematode species, and a recent screening of C. sativus accessions in the U.S. National Plant Germplasm collection did not identify sources of resistance. Thus,autotetraploids of Cucumis sativus and C. metuliferus were created to recover fertile resistant interspecific progeny. Autotetraploids were obtained at the highest rate when seeds were immersed in 0.5% colchicine for a period of 6 to 8 hrs. Treatment durations less than 6 hrs produced few tetraploids, and durations of 10 hrs or more were lethal to seeds or developing seedlings. Crosses between C. sativus and C. metuliferus were made using diploid and tetraploid lines in all possible combinations, including reciprocals. Fruit development occurred in crosses when diploid and tetraploid C. sativus were used as the female parent. However, seeds developed only in fruit of C. sativus (4n) ×C. metuliferus (2n) crossings. Seeds from these crosses, however,were flat and not viable. No fruit development occurred in crosses whereC. metuliferus was used as the female parent. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and preliminary characterization of a new species (amphidiploid) in Cucumis

A successful interspecific hybridization between cucumber (Cucumis sativus L., 2n = 14) and a wild it Cucumis species, C. hystrix Chakr. (2n = 24) was made via embryo rescue. Hybrid plants (2n = 19; 7 from cucumber and 12 from C. hystrix) were sterile, but morphologically uniform. Self-pollination and backcrossing of F₁ hybrid plants to either parent confirmed presence of both male- and female-sterility that were likely caused by lack of homology and improper pairing during meiosis. While the multiple-branching habit, densely brown hairs (on corolla and pistil), orange-yellow corolla, and ovate fruit of F₁ hybrid plants were similar to that of the C. hystrix parent, the appearance of the first pistillate flower was more similar to that of C. sativus parent. The diameter and internode length of the stem, and the shape and size of leaves and flowers were intermediate when compared to the parents. The chromosome number in the hybrid was doubled through somaclonal variation during embryo culture and regeneration process to restore the fertility. Pollen grains were released and fruits with viable seeds matured on fertile, synthetic amphidiploid plants. The results from flow cytometry indicated that, on average, 7.3% of the morphologically unique regenerants had the 4C DNA content of 2.35 pg relative to the 2C DNA content of the original F₁ hybrid at 1.17 pg and, therefore, were likely chromosome-doubled F₁ hybrids (2n = 38). Nutrition alanalysis indicated that the synthetic species had higher protein (0.78%)and mineral (0.35%) content compared to the normal pickling cucumber(0.62% and 0.27%, respectively), and could be considered a new Cucumis crop having a special place in the future agriculture. Preliminarily evaluation indicates that C. hystrix possesses a high level of root-knot nematode resistance, and that this resistance is partially expressed in the interspecific F₁ and chromosome-doubled F₁. This and the fact that the fruit morphology of the fertile amphidiploid differs during the growing season (e.g., short and long fruit) suggest that it could be useful in broadening the germplasm base of cucumber. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Different sex phenotypes of Cucumis sativus L. and C. melo L. and their endogenous gibberellin activity

Summary Gibberellins were extracted from seeds and green plants of different sex types of the closely related species Cucumis sativus L. (cucumber) and C. melo L. (muskmelon). Both seeds and green plants of monoecious and andromonoecious lines of C. sativus contained significantly higher gibberellin levels at all growth stages tested than did a gynoecious line. Gibberellin activity in the monoecious and andromonoecious C. sativus line reached a maximum at the growth stage corresponding to flower differentiation at cotyledonary and first leaf axils. Vernalization of seeds of gynoecious plants resulted in increased male tendency correlated with increased gibberellin activity. In contrast, monoecious and andromonoecious lines of C. melo were gibberellin deficient relative to hermaphroditic and gynoecious lines.Journal Article No 5534 from the Michigan Agricultural Experiment Station. This work was supported by a grant from the Herman Frasch Foundation.     

Overcoming hybridization barriers between pea and some of its wild relatives

Pea would benefit from the plasticity and adaptability of its cross-incompatible relatives Pisum fulvum and Lathyrus sativus L., and we have tested reciprocal sexual crossings by manually cross-pollinating plants of genotypes of these three species. Studies of in situ germination of pollen grains on stigmata showed that pollen tubes were generally unable to germinate or could not reach the ovary. A few putative hybrid pods were nevertheless harvested, with one grain per pod germinated in vitro, then micropropagated for flow cytometry, isoenzyme, molecular (ribosomal ITS PCR-RFLP) and genomic in situ hybridization (GISH) studies. One such grain was recovered from an inter-generic cross of P. sativum x L. sativus and four from an inter-specific P. sativum x P. fulvumcross. A strong cross-incompatibility was shown between pea and grass pea, where the putative hybrid turned out to be pea. Conversely, with the interspecific, P. sativum x P. fulvum cross, flow cytometry and isoenzymes with leaf tissues strongly suggested hybridity, while molecular approaches and GISH confirmed the production of inter-specific hybrids, and without the need for a wild type P. sativum accession as a bridging cross.     

Investigations on F1 and F2 hybrids between Brassica oleraceae Var. Acephala and Raphanus sativus

A cross was made between B. oleraceae var. acephala and R. sativus. The use of a piece of cotton soaked with the growth regulator, N-m-tolyphthalamic acid at 100 ppm and attached to the pedicel at the time of pollination resulted in set of several pods with one viable seed. The hybrid kale x radish appeared vegetatively intermediate between the parents except for the flower color which resembled the radish. The F₁ plant propagated asexually and maintained under screen isolation cages with pollinating insects for a period of four years yielded only one viable F₂ seed. The single F₂ plant obtained, an allotetraploid, failed to yield any fertile seeds through selfing. Backcrossing of this F₂ plant to the radish has yielded two seeds.Department of Horticulture, Michigan State UniversityWith 7 figuresJournal article No. 2923. From the Michigan Agricultural Expreriment Station.     

Genetics of Seed Yield and its Components in Common Bean (Phaseolus vulgaris L.) of Middle-American Origin

Genetic variance, heritability, and expected response from selection arc useful in devising alternative methods and criteria of: selection. The objectives of this study were to estimate these for seed yield and its components from 200 F₂: populations involving 80 cultivars and lines of mostly small-seeded dry bush bean (Phaseolus vulgaris L.) of habits growth I, II, and III of Middle-American origin. All cultivars and lines were crossed in eight sets of ten parents each in a Design II mating system. The F₂ populations, without parents, were evaluated in the field in a replicates-in-sets design at two locations in Colombia in 1983. Estimates of additive genetic variance were significant for yield, pods/m², seeds/pod, and seed weight. Interaction with environments was also significant. Values for nonadditive genetic variance were not significant for either yield or yield components. The estimates of narrow sense heritability, based on the F₂ population mean and unbiased by genotype x environment interaction, were 0.21 ± 0.13 for yield. 20 ± 0.13 for pods/m², 0.57 ± 0.13 for seeds/pod, and 0.74 ± 0.15 for seed weight. The expected direct response from selection of the top 20 % of F₂ populations for yield per se would result in a 4.30 % increase in yield with a correlated response of 0.21 % in seed weight. In contrast, the expected gain from direct selection for seed weight would result in a 11.76 % increase in seed weight with a, correlated gain of 0.28 % for yield. Direct selection for pods/m² would decrease yield, seeds/pod and seed weight, while direct selection for seeds/pod would reduce pods/m² and seed weight but increase seed yield by 0.37 %. Data on yield from replicated trials in the early segregating generations could be utilized for identification and selection of promising crosses and families or lines with crosses for dry bean yield improvement.