Pod shattering in grain legumes: emerging genetic and environment-related patterns

A reduction in pod shattering is one of the main components of grain legume domestication. Despite this, many domesticated legumes suffer serious yield losses due to shattering, particularly under arid conditions. Mutations related to pod shattering modify the twisting force of pod walls or the structural strength of the dehiscence zone in pod sutures. At a molecular level, a growing body of evidence indicates that these changes are controlled by a relatively small number of key genes that have been selected in parallel across grain legume species, supporting partial molecular convergence. Legume homologs of Arabidopsis thaliana silique shattering genes play only minor roles in legume pod shattering. Most domesticated grain legume species contain multiple shattering-resistance genes, with mutants of each gene typically showing only partial shattering resistance. Hence, crosses between varieties with different genes lead to transgressive segregation of shattering alleles, producing plants with either enhanced shattering resistance or atavistic susceptibility to the trait. The frequency of these resistance pod-shattering alleles is often positively correlated with environmental aridity. The continued development of pod-shattering-related functional information will be vital for breeding crops that are suited to the increasingly arid conditions expected in the coming decades.

Recent genetic, genomic, and phenotypic studies of pod shattering in grain legumes lay the foundation for breeding crops suited for increasingly arid conditions.     

Nitrogen fixation in several grain legume species with contrasting sensitivities to copper nutrition

The nitrogen fixation response to copper nutrition in faba bean, yellow lupin and soybean was studied. Copper nutrition significantly increased the pod yields of all tested grain legumes but faba bean gave the greatest Cu-use efficiency for pod and grain production. The accumulation of dry matter in vegetative parts, nodules, N and leghemoglobin concentration in nodules and nitrogen accumulation in the whole plants were increased by copper supply in faba bean and yellow lupin in contrast with soybean. Cu nutrition significantly increased the Cu concentrations in nodules of all cultivated plants. The differential sensitivity of N₂ fixation in tested grain legume species to copper nutrition could be connected with the level of phenols in nodules and depended on both the host plants and strains of rhizobia, which differ in their ability to produce catechol-like siderophores. Copper requirements by symbiotic N₂ fixation could also depend on the nature of phenols in nodules (presence of o-dihydroxyphenols or number of hydroxyls in molecule).     

Unusual Network of Internal Phloem in the Pod Mesocarp of Cowpea [Vigna unguiculata (L.) Walp. (Fabaceae)]

A mycelium-like network of internal phloem was observed in theinner mesocarp of the lateral pod walls of the fruit of certaingenotypes of cowpea [Vigna unguiculata (L.) Walp.] In the cultivarVita 3, the network consists of single, or rarely double, strandsof sieve elements and associated phloem parenchyma, orientedmainly parallel with the fibres of the adjacent endocarp, andstretching marginally beyond the sheets of fibres to connectabove and below with the outermost phloem of the longitudinalstrands of the dorsal and ventral sutures of the fruit. Theinternal phloem network does not relate conformationally to,or interconnect with the conventional (xylem+phloem) vasculatureof the mid mesocarp of the pod wall. In Vita 3, sieve elementsdifferentiate in the internal phloem after those in the majorveins of the pod, but before the presumptive endocarp fibrescommence wall thickening. The pod walls of twenty-one otherspecies of legumes proved negative for internal phloem, whileof nine varied genotypes of cowpea examined, six proved positive,three negative for the trait. Presence of internal phloem incowpea is not always associated with presence of endocarp fibresor necessarily with large fruits with large seeds. Possiblefunctions suggested for the phloem network are to provide assimilatesfor fibre wall thickening or to transport solutes to or fromsites of temporary storage in the fleshy inner layers of thepod wall. Internal phloem, legume fruit, translocation, mesocarp, pod wall, Vigna unguiculata, cowpea     

Nuclear DNA Amounts in Roses

Nuclei isolated from young leaves were stained with propidiumiodide (PI) and their fluorescence intensities were measuredby flow cytometry. The ratio of fluorescence intensities offour calibration standards and 34 roses to an internal standard,parsley (Petroselinum crispum), provided a basis for estimatingthe DNA amounts of P. crispum and rose. The 2C DNA amount ofP. crispum(2 n = 22) was estimated as 4.46 pg (s.d. ±0.08 pg). The 2C DNA amounts of diploid roses (2n = 14) variedbetween subgenera, sections and cultivars, and ranged from 0.78pg (s.d. ± 0.08 pg) in Rosa xanthina and R. sericea(sectionPimpinellifoliae) to 1.29 pg (s.d. ± 0.08 pg) in ‘Félicitéet Perpétue’ (Hybrid Sempervirens). Within eachsection, the DNA amounts of diploid species were similar. Inthe sections Carolinae and Cinnamomeae, DNA amounts were proportionalto ploidy numbers. In the Pimpinellifoliae, DNA amounts of tetraploidswere disproportionately larger than those of diploids whichsuggests that they originated as hybrids with species of sectionswith larger DNA amounts. Ratios of the fluorescence intensitiesof nuclei of roses to P. crispum(internal standard) were alsomeasured using 4',6-diamidino-2-phenylindole (DAPI) which bindspreferentially to AT base pairs. These DAPI ratios were lowerthan, but closely correlated (r² = 0.997) with PI ratios. Fluorescenceintensities of either PI or DAPI-stained nuclei of roses canbe used as rapid indicators of ploidy if variation in the DNAamounts between different taxonomic groups is taken into account.Copyright 2000 Annals of Botany Company Flow cytometry, nuclear DNA amounts, Petroselinum crispum, phenolics, Rosa, roses     

Narrow-leafed Lupins with Restricted Branching

Crop phenology is one of the most important characters influencingproductivity in a given environment. Narrow-leafed lupin (Lupinusangustifolius L.) is a major grain legume crop in southern Australiawith general phenological adaptation to this Mediterranean-typeenvironment. However, it is an indeterminate crop with severalassociated limitations to productivity, such as overlappingvegetative and reproductive growth, late grain filling and sometimesexcessive vegetative growth. Here we studied two novel typesof narrow-leafed lupin with restricted branching, which mightbe useful for overcoming these problems. These restricted branchinglupins arose spontaneously within a breeding population, inthe case of ‘Tallerack’, and within a farmer's cropin the case of ‘ Hurst’ and we compared them withthe ‘Merrit’, which is widely grown and has thenormal indeterminate branching habit. The morphology and developmentof the main shoot of these genotypes were similar. However,‘Hurst’ had much larger leaves. There were alsostriking differences in the lateral branches of the restrictedbranching types; they had fewer leaves than ‘Merrit’and flowered earlier. These differences were most marked in‘ Hurst’, where the upper main stem branches werereduced to a single floret in the axil of main stem leaves,and these flowers often exhibited abnormal morphology. Copyright2000 Annals of Botany Company Lupinus angustifolius L., narrow-leafed lupin, adaptation, development, morphology, branching, leaves, mutant, plastochron, phyllochron, floral initiation, flowering.     

Flow cytometric analysis of somatic embryos, shoots, and calli of the cactus Copiapoa tenuissima Ritt. forma monstruosa

Flow cytometry was used for analyzing DNA contents of nuclei isolated from in vitro grown somatic embryos, shoots and calli, as well as mammillae of in vivo grown shoots of cactus, Copiapoa tenuissima Ritt. forma monstruosa. Endoreduplication was detected in both in vitro grown somatic embryos, shoots and calli and in mammillae derived from in vivo grown shoots. However, the lowest ploidy levels ranged from 2C to 4C in somatic embryos, and reaching up to 32C for in vitro grown shoots and calli from mammillae. Whereas, ploidy levels of in vivo-derived mammillae ranged from 2C to 16C. The presence of 2,4-dichlorophenoxyacetic acid (2,4-D) in the culture medium had no influence on levels of ploidy of regenerated tissues. The mean genome size of cactus was calculated as 2C = 2.87 ± 0.05 picogram (pg).     

Changes in the composition of exocellular proteins of suspension-cultured Lupinus albus cells in response to fungal elicitors or CuCl2

Among many aspects of plant defence responses to pathogenicinfection are changes in the composition of the exocellularmatrix. To study potential defences in white lupin (Lupinusalbus L.), suspension-cultured cells were treated for 24 h withone of three different elicitors: CuCl₂, and two fungal elicitorpreparations from purified cell walls of yeast and ColletotrichumIindemuthianum. Two subsets of exocellular proteins: ionicallyboundwall proteins and proteins secreted into culture medium, wereisolated, and their patterns compared following electrophoreticseparation. Only a few proteins were observed in culture filtrateswith dominating bands at 27, 33, and 42 kDa. About 30 proteinswere observed in cell wall extracts. Changes in protein intensitiesevoked by elicitor treatments depended on the type of elicitorused, the age and composition of lupin cell culture, and concentrationof applied fungal elicitor. Based on these observations, tenproteins were chosen for N-terminal sequencing, and sequences5–30 amino acids long for nine proteins were obtained.Three of the major proteins sequenced were identified as acidicexocellular chitinase, polygalacturonaseinhibiting protein,and germin/oxalate oxidase. Key words: Lupinus aibus, defence response, exocellular proteins, elicitation, N-terminal amino acid sequencing, suspension culture     

Changes in Carbohydrate, Amino Acid and Phenol Contents in Cocoa Pods from Three Clones after Infection with Phytophthora megakarya Bra. and Grif.

Mature pods from three clones ofTheobroma cacaoL., differingin their susceptibility toPhytophthora megakaryaBra. and Grif.,were infected with the fungal mycelium. Variations of the contentsin carbohydrates, ketohexoses, amino acids, phenols and flavonol,and hydroxycinnamic derivatives were followed in the cortexfor 4d. After pod infection, the amount of carbohydrates decreasedmore rapidly in the clone SNK10 (highly susceptible) than inthe clones SNK413 (low susceptibility) and ICS95 (mildly susceptible),suggesting their utilization by the fungus. At the same time,the amount of ketohexoses decreased by 22% in the clone SNK10,remained almost constant in the clone SNK413, and increasedby 53% in the clone ICS95. The content of amino acids increasedwith time in the pods of the three clones. The results suggestthat the amino acid variation is related to pod aging and tothe infection. Four days after treatment, an increase in phenolicswas measured in all cases. The increase in flavonol and hydroxycinnamicderivatives was related to the wounding and to the infectionof the pods. DuringPhytophthorablack pod development, variationsof the contents in the biochemicals studied herein were genotype-dependent,and the patterns of the changes could be related, at least inpart, to the susceptibility of the genotype toP. megakarya. Theobroma cacaoL.; cocoa; black pod; plant/fungus interaction; susceptibility     

Vertical heterogeneity of DNA ploidy level assessed by flow cytometry in calli of Passiflora Cincinnata

During in vitro culture conditions, callus tissue is exposed to different intensities of environmental stress, which may induce somaclonal variation. Among the possible resulting abnormalities, callus cells can exhibit distinct DNA ploidy levels, a type of somaclonal variation associated with euploidy and/or aneuploidy. As somaclonal variation has been regarded as both a positive and negative phenomenon, the development of strategies to carefully assess the stability of DNA ploidy level within callus tissue is highly valuable. To this end, the present work aimed to evaluate the presence of intra- and inter-calli heterogeneity in relation to DNA ploidy level and nuclei density by flow cytometry. Calli were induced from cotyledonary leaves of Passiflora cincinnata, a wild passion fruit species. Embryogenic friable calli cultivated for 2, 6, and 9 mo were classified as young, intermediary, and old, respectively. These calli were horizontally sliced from the bottom-up at approximately the same thickness, and a total of 160 layers were evaluated by flow cytometry. Inter- and intra-calli heterogeneities were detected in relation to nuclei density and DNA ploidy level. Additional analysis was performed to identify the most proliferative layer. We conclude that care must be taken when using callus as source material for flow cytometry, since one portion cannot represent the whole cell mass. Moreover, in order to prevent the emergence of undesired ploidies during clonal propagation, callus culture time should not be prolonged.     

A Physiological Analysis of the Branching Pattern in Sequential Types of Groundnut in Relation to the Fruiting Nodes and the Total Mature Pods Produced

The branching pattern of eight sequential branching types ofgroundnut was studied and the contribution of each node (fruitingpoint) of the n, n+1 and n+2 branches (if present) to the totalnumber of mature pods per plant ascertained. The results indicatedthat n+2 branches were present in several varieties and theircontribution to mature pods was significant in some of them.The first three nodes of the n+1 branches contributed from 50.6per cent (in a variety which had significantly more n+2 branches)to 88 per cent in other varieties. The results also indicatedthat the contribution of the late formed n+1 branches was lowand the total mature pods produced from all nodes decreasedwith each successive (chronologically) n+1 branch in all thevarieties studied. Neither the total number of n+1 branchesnor the number of mature pods per node was related to the podnumber or pod yield, but the total number of fruiting pointsfrom all branches showed a high correlation with pod yield andmature pod number at harvest. The results suggest that for higherpod yield it may be desirable to have only a few n+1 branches(4 or 5) but with more fruiting points on each branch. Arachis hypogaea, branching pattern, sequential types, fruiting points     

European Origin of Bradyrhizobium Populations Infecting Lupins and Serradella in Soils of Western Australia and South Africa

We applied a multilocus phylogenetic approach to elucidate the origin of serradella and lupin Bradyrhizobium strains that persist in soils of Western Australia and South Africa. The selected strains belonged to different randomly amplified polymorphic DNA (RAPD)-PCR clusters that were distinct from RAPD clusters of applied inoculant strains. Phylogenetic analyses were performed with nodulation genes (nodA, nodZ, nolL, noeI), housekeeping genes (dnaK, recA, glnII, atpD), and 16S-23S rRNA intergenic transcribed spacer sequences. Housekeeping gene phylogenies revealed that all serradella and Lupinus cosentinii isolates from Western Australia and three of five South African narrow-leaf lupin strains were intermingled with the strains of Bradyrhizobium canariense, forming a well supported branch on each of the trees. All nodA gene sequences of the lupin and serradella bradyrhizobia formed a single branch, referred to as clade II, together with the sequences of other lupin and serradella strains. Similar patterns were detected in nodZ and nolL trees. In contrast, nodA sequences of the strains isolated from native Australian legumes formed either a new branch called clade IV or belonged to clade I or III, whereas their nonsymbiotic genes grouped outside the B. canariense branch. These data suggest that the lupin and serradella strains, including the strains from uncultivated L.cosentinii plants, are descendants of strains that most likely were brought from Europe accidentally with lupin and serradella seeds. The observed dominance of B. canariense strains may be related to this species' adaptation to acid soils common in Western Australia and South Africa and, presumably, to their intrinsic ability to compete for nodulation of lupins and serradella.     

Biological Nitrogen Fixation in Pachyrhizus ahipa (Wedd.) Parodi

The patterns of plant growth and N₂ fixation capability in Pachyrhizusahipa (Wedd) Parodi inoculated with Bradyrhizobium ‘PachyrhizusSpec 1’ strains (Lipha Tech) were investigated in a zero-Nculture system under greenhouse conditions The P ahipa plantis day-neutral with respect to reproductive development Competitionoccurred between the two storage organs (legume and tuber) andprevented high tuber yield in P ahipa The symbiotic effectivenessof the association was high, as the profuse nodulation providedthe inoculated plants with adequate amounts of N Nodules werepresent throughout the cycle of P ahipa The change in rate ofN₂ fixation (RNF) and relative growth rate (RGR) was almostparallel during ontogenesis The developmental pattern of N₂fixation activity revealed that 65% of total N₂ fixation occurredafter N began to accumulate in the reproductive (pod wall plusseed) tissue During pod filling allocation of N compounds tothe seeds exceeded N₂ fixation, the pod walls being the primarysource of redistributed N, followed by the leaves. Pachyrhizus ahipa (Wedd) Parodi, ahipa, tuber crop, dinitrogen fixation, dry matter, N partitioning, reproductive growth     

Comparisons of the Respiratory Effluxes of Nodules and Roots in Six Temperate Legumes

The specific respiration rates of nodulated root systems, ofnodules and of roots were determined during active nitrogenfixation in soya bean, navy bean, pea, lucerne, red clover andwhite clover, by measurements on whole plants before and afterthe removal of nodule populations. Similar measurements weremade on comparable populations of the six legumes, lacking nodulesbut receiving abundant nitrate-nitrogen, to determine the specificrespiration of their roots. All plants were grown in a controlled-environmentclimate which fostered rapid growth. The specific respiration rates of nodulated root systems ofthe three grain and three forage legumes during a 7–14-dayperiod of vegetative growth varied between 10 and 17 mg CO₂g^–1 (dry weight) h^–1. This mean value consistedof two components: a specific root respiration rate of 6–9mg CO₂ g^–1 h^–1 and a specific nodule respirationrate of 22–46 mg CO₂ g^–1 h^–1. Nodule respirationaccounted for 42–70 per cent of nodulated root respiration;nodule weight accounted for 12–40 per cent of nodulatedroot weight. The specific respiration rates of roots lackingnodules and utilizing nitrate nitrogen were generally 20–30per cent greater than the equivalent rates of roots from nodulatedplants. The measured respiratory effluxes are discussed in thecontext of nitrogen nitrogen fixation, nitrate assimilation. Glycine max, Phaseolus vulgaris, Pisum sativum, Medicago sativa, Trifolium pratense, Trifolium repens, soya bean, navy bean, pea, lucerne, red clover, white clover, nodule respiration, root respiration, fixation, nitrate assimilation     

Factors Affecting Shedding of Flowers in Soybean (Glycine max (L.) Merrill)

Flower shedding in soybean, Glycine max (L.) Merrill, was studiedusing cultivar ‘Clark’, isoline E₁t, which has relativelylong racemes for convenient identification and observation ofindividual flowers. On each raceme studied, pod set was greatestat the proximal (basal) positions, whereas shedding was greatestat the most distal positions. When proximal flowers were removedas they reached anthesis, pod set increased at the more distalpositions. Pod set was increased in some instances by applicationof water directly to the ovaries as a drop in the calyx cup.Peroxidase activity changed in parallel with ovary development,increasing rapidly in growing pods but not in shedding flowers.Increases in flower peroxidase was mainly in ovary walls. Flowerstaken at or near anthesis from positions with high percent podset could be grown in vitro with especially good ovary enlargement,whereas ovaries in flowers taken from positions of low pod setdid not enlarge in culture. Unidentified substances were extracted from young pods which,when incorporated into lanolin and tested in an in situ bioassay,could mimic the effect of proximal flowers in inducing sheddingof distal flowers. Indole-3-acetic acid resembled the extractedmaterials in inducing shedding, but differed by eliciting side-effectsthat extracts did not. The growth substances abscisic acid,gibberellic acid, and benzyladenine did not promote sheddingin the in situ test. The evidence was taken to indicate that soybean flower sheddingis induced in distal flowers by substances from the more proximal,fertilized ovaries, and that this is possibly due to interferencewith some of the intense metabolic changes that follow pollinationand fertilization.     

Infection and Nodule Development in Aotus ericoides (Vent.) G. Don, A Woody Native Australian Legume

Infection and nodule development were studied by light and electronmicroscopy in Aotus ericoides, a woody native Australian legume,inoculated with a slow-growing field isolate of Rhizobium. Rhizobiabound to straight, but not deformed, root hairs, as detectedby immunofluorescence. Neither markedly curled root hairs norroot hairs with infection threads were seen. Nodules were indeterminate(astragaloid), with a peripheral meristematic layer, few vasculartraces and both infected and uninfected cells in the centralinfected zone. Infection threads containing contorted bacteriawere present throughout the nodule. Swollen, rod-shaped bacteriain infected cells were in groups in vesicles bounded by plasmalemma-derivedperibacteroid membranes. Senescence in infected cells was associatedwith accumulation of a fibrillar matrix inside peribacteroidmembranes, distortion of bacteria and destruction of most cytoplasmiccontents of the bacteria and host cells; however, most bacterialand plant membranes and plant cell walls remained intact. Ineffectivenesswas associated with relatively little, short-lived infectedtissue. Events in infection and nodule development were similarto those in most herbaceous legumes but showed characters ofboth determinate and indeterminate nodules. Key words: Bacteroids, Legume, Nitrogen-fixing, Nodule, Rhizobium     

Most organs of sugar-beet (<Emphasis Type="Italic">Beta vulgaris</Emphasis> L.) plants at the vegetative and reproductive stages of development are polysomatic

Polysomaty was studied using flow cytometry in different organs of diploid, triploid and tetraploid sugar-beet (Beta vulgaris L.) plants, in the first (at harvest) and the second (at the height of the blooming period) year of development. Of the organs/parts of organs of the vegetative plant that developed during the first year, only the leaf lamina did not contain endopolyploid cells; in all others, one to three endocycles had occurred. The second-year seed-crop plant was also highly polysomatic; even in reproductive organs such as the flower and pericarp the endopolyploid cells were present (up to 8C and 32C, respectively). At this stage of development no endocycles occurred in the leaf lamina, flower bract, and inflorescence bract. The parts of the plant with no endopolyploid cells are recommended for ploidy estimation, and as a material suitable for micropropagation and genetic manipulations. Endoreduplication, up to 32C (64Cx), was organ-specific and correlated negatively with plant ploidy. The highest mean C-value, over 7, was in the diploid, in the basal part of the oldest leaf petiole in the first-year plant, and in the storage parenchyma of the root in the second-year seed-crop plant. The results confirm that higher endopolyploidy occurs in plants with a smaller 2C DNA amount than in those with a larger one. The significance of endopolyploidization in development of sugar-beet plant organs is discussed.     

Fine mapping of a major quantitative trait locus that regulates pod shattering in soybean

Legumes represent the second most important family of crop plants, accounting for ~27 % of the world’s crop production. While some legumes are grown as forages or vegetables, most crop legumes are grown for harvesting their nutritious seeds. The legume seeds are contained in the pod, which is composed of a single seed-bearing carpel that, when matures, splits open along two seams, a process called pod dehiscence or pod shattering. Pod shattering before or during harvest causes yield losses of grain legumes. Moreover, the dominant shattering trait of the wild progenitors is a limiting factor for efficient introgression of value-added traits into elite breeding lines. Knowledge of the genetic mechanisms underlying pod shattering will facilitate breeding of shattering-resistant varieties, expedite introgression of agronomically favorable traits from wild species to elite breeding lines, and enrich our understanding of the evolution of seed dispersal and crop domestication in diverse crop species. Here we report fine mapping of a major quantitative trait locus (designated as qPDH1) that regulates pod shattering in soybean (Glycine max). A combination of linkage and association mapping allowed us to delimit the qPDH1 locus within a 47-kb region on chromosome 16. The data reported here will facilitate positional cloning of the underlying gene and the development of breeder-friendly genetic markers for marker-assisted selection in soybean.     

Patterns of Endopolyploidy During Seedling Development in Cabbage (Brassica oleracea L.)

Flow cytometric analysis of nuclear DNA contents of somatictissues of cabbage (Brassica oleracea L.) has revealed extensiveendopolyploidization, resulting in tissues that comprise mixturesof cells with different DNA contents, ranging from 2C to 16C.Patterns of endopolyploidy are specific to each developmentalstage. Multiple polyploidy was not present in the embryos ofdry seeds. Rapid endoreduplication occurred in the radicle andthe hypocotyl of the embryos during seed germination. Furtherendoreduplication cycles were detected in all tissues exceptthose of the shoot tips. In five cabbage cultivars tested, seedlingscontained cells of four ploidy levels, corresponding to 2C,4C, 8C and 16C. Multiploidy may be an integral part of differentiationprograms in cabbage plants. The biological significance of endoreduplicationin cabbage plants is discussed. Copyright 2001 Annals of BotanyCompany Cabbage (Brassica oleracea L.), endopolyploidy, endoreduplication, flow cytometry     

Developmental and Varietal Comparisons of Pod Carboxylase Levels in Pisum sativum L.

The activities of phosphoenolpyruvate (PEP) carboxylase andribulose-1, 5-bisphosphate (RuDP) carboxylase have been determinedin the developing pod walls of six genotypes of Pisum sativum.Genotypes were chosen which varied in pod characters such aschlorophyll content and tissue morphology, which it was hopedwould be associated with variation in carboxylase levels. Whilst both enzymes were detected in all genotypes, the levelsof activity varied considerably with pod type and with age.In general RuDP carboxylase activity correlated with chlorophyllconcentration, and yellow podded types had considerably lessactivity than green types. The yellow podded genotypes, however,contained significantly higher levels of PEP carboxylase which,in terms of total carboxylase activity, compensated for thelower RuDP carboxylase levels. The activities of both enzymes were determined within the endocarpand within the mesocarp plus exocarp, using 16-day-old pods.All genotypes showed an enrichment for PEP carboxylase in theendocarp and all but one genotype showed a similar enrichmentfor RuDP carboxylase activity in this layer. The role of the carboxylase enzymes within the pod wall is discussedand it is suggested that their main function may be to maintainan appropriate level of CO₂ within the pod cavity as well asrecycling carbon to the developing seeds. Pisum savitum L., pea, pods, carboxylase levels, genetic variation