Spatial aluminium sensitivity of root apices of two common bean (Phaseolus vulgaris L.) genotypes with contrasting aluminium resistance

The initial response of plants to aluminium (Al) is an inhibition of root elongation. In the present study, short and medium-term effects of Al treatment (20 muM) on root growth and Al accumulation of two common bean (Phaseolus vulgaris L.) genotypes, VAX-1 (Al-sensitive) and Quimbaya (Al-resistant), were studied. Root elongation of both genotypes was severely inhibited during the first 3-4 h of Al treatment. Thereafter, both genotypes showed gradual recovery. However, this recovery continued in genotype Quimbaya until the root elongation rate reached the level of the control (without Al) while the genotype VAX-1 was increasingly damaged by Al after 12 h of Al treatment. Short-term Al treatment (90 microM Al) to different zones of the root apex using agarose blocks corroborated the importance of the transition zone (TZ, 1-2 mm) as a main target of Al. However, Al applied to the elongation zone (EZ) also contributed to the overall inhibition of root elongation. Enhanced inhibition of root elongation during the initial 4 h of Al treatment was related to high Al accumulation in root apices in both genotypes (Quimbaya>VAX-1). Recovery from Al stress was reflected by decreasing Al contents especially in the TZ, but also in the EZ. After 24 h of Al treatment the high Al resistance of Quimbaya was reflected by much lower Al contents in the entire root apex. The results confirmed that genotypic differences in Al resistance in common bean are built up during medium-term exposure of the roots to Al. For this acquisition of Al resistance, the activation and maintenance of an Al exclusion mechanism, especially in the TZ but also in the EZ, appears to be decisive.     

Intracellular distribution and binding state of aluminum in root apices of two common bean (Phaseolus vulgaris) genotypes in relation to Al toxicity

The role of the intracellular distribution and binding state of aluminum (Al) in Al toxicity, using Al exchange and Al fractionation methodologies, were studied in two common bean ( Phaseolus vulgaris L.) genotypes differing in Al resistance. These two genotypes are characterized by a similar initial period (4 h) of Al sensitivity followed by a contrasting recovery period (8–24 h). A higher initial Al accumulation in Quimbaya (Al resistant) in the 5-mm root apex compared with VAX-1 (Al sensitive) could be related to its higher content of unmethylated pectin and thus higher negative charge of the cell walls (CWs). The binding state and cellular distribution of Al in the root apices revealed that the root elongation rate was significantly negatively correlated with the free apoplastic and the stable-bound, not citrate-exchangeable CW Al representing the most important Al fraction in the root apex (80%), but not with the symplastic and the labile-bound, citrate-exchangeable CW Al. It is postulated that the induced and sustained recovery from the initial Al stress in the Al-resistant genotype Quimbaya requires reducing the stable-bound Al in the apoplast thus allowing cell elongation and division to resume.     

Races of common bean (Phaseolus vulgaris,Fabaceae)

Evidence for genetic diversity in cultivated common bean (Phaseolus vulgaris) is reviewed. Multivariate statistical analyses of morphological, agronomic, and molecular data, as well as other available information on Latin American landraces representing various geographical and ecological regions of their primary centers of domestications in the Americas, reveal the existence of two major groups of germplasm: Middle American and Andean South American, which could be further divided into six races. Three races originated in Middle America (races Durango, Jalisco, and Mesoamerica) and three in Andean South America (races Chile, Nueva Granada, and Peru). Their distinctive characteristics and their relationships with previously reported gene pools are discussed.     

Inheritance of partial resistance to bean rust in the common bean (Phaseolus vulgaris L.)

The inheritance of partial resistance within eight bean cultivars to a single-pustule isolate of bean rust was studied by means of a F₁ diallel test. General combining ability (GCA) and specific combining ability (SCA) were very highly significant over two seasons and in interaction with seasons. The partitioning of the sums of squares indicated the greater importance of GCA in the inheritance of the resistance. Reciprocal effects were not significant. The estimates of narrow-sense heritability in the two seasons were 0.899 ± 0.056 and 0.603 ± 0.065.     

Basal root whorl number: a modulator of phosphorus acquisition in common bean (Phaseolus vulgaris)

Background and Aims

Root architectural phenes enhancing topsoil foraging are important for phosphorus acquisition. In this study, the utility of a novel phene is described, basal root whorl number (BRWN), that has significant effects on topsoil foraging in common bean (Phaseolus vulgaris).

Methods

Whorls are defined as distinct tiers of basal roots that emerge in a tetrarch fashion along the base of the hypocotyl. Wild and domesticated bean taxa as well as two recombinant inbred line (RIL) populations were screened for BRWN and basal root number (BRN). A set of six RILs contrasting for BRWN was evaluated for performance under low phosphorus availability in the greenhouse and in the field. In the greenhouse, plants were grown in a sand–soil media with low or high phosphorus availability. In the field, plants were grown in an Oxisol in Mozambique under low and moderate phosphorus availability.

Key Results

Wild bean accessions tended to have a BRWN of one or two, whereas cultivated accessions had BRWN reaching four and sometimes five. BRWN and BRN did not vary with phosphorus availability, i.e. BRWN was not a plastic trait in these genotypes. Greater BRWN was beneficial for phosphorus acquisition in low phosphorus soil. Genotypes with three whorls had almost twice the shoot biomass, greater root length and greater leaf area than related genotypes with two whorls. In low phosphorus soil, shoot phosphorus content was strongly correlated with BRWN (R² = 0·64 in the greenhouse and R² = 0·88 in the field). Genotypes with three whorls had shallower root systems with a greater range of basal root growth angles (from 10 to 45 ° from horizontal) than genotypes with two whorls (angles ranged from 60 to 85 ° from horizontal).

Conclusions

The results indicate that BRWN is associated with increased phosphorus acquisition and that this trait may have value for selection of genotypes with better performance in low phosphorus soils.     

Monosomics in common bean,Phaseolus vulgaris

Summary Two monosomics of Phaseolus vulgaris (2n = 22) were found among selfed progeny of plants treated with colchicine. The monosomic chromosomes involved were identified as chromosomes H and J according to the previously suggested Giemsa karyotype. Both monosomic plants had slower growth rate and smaller size as compared with their respective euploid sibs. However, no apparent morphological characteristics distinguished the two monosomics. The frequencies of transmission through selfing of monosomics H and J were 9% and 10 % respectively.     

Multiple paternity in common bean (Phaseolus vulgaris L., Fabaceae)

We report on two field experiments that were conducted in 1991 and 1992 at the South Coast Extension and Research Center, Irvine, CA, to study the incidence of multiple paternity in the common bean (Phaseolus vulgaris L.). Hypocotyl color and shikimate dehydrogenase (Skdh) isozymes were used as genetic markers. The white-seeded cultivar ‘Ferry Morse 53’ (FM 53) was used as the female parent. This cultivar is homozygous recessive (pp) for hypocotyl color. The pollen source parents were three homozygous dominant (PP) purple-hypocotyled, black-seeded cultivars. Three cultivars, ‘ICA Pijao,’ G4459, and the maternal parent FM 53, are of Mesoamerican origin and homozygous for the fast (F) allele at the Skdh locus. The other cultivar, Black Valentine, is of Andean origin and is homozygous for the slow (S) allele at the Skdh locus. Overall, 6 125 pods were obtained from 57 and 111 plants harvested individually in 1991 and 1992, respectively. All progeny, 28938 seeds, were scored for hypocotyl color at the seedling stage. The purple-hypocotyled seedlings were genotyped for the Skdh locus to identify their pollen parents. Multiple paternity was identified in all the pods with hybrid seeds (i.e., those of intercultivar crosses) at 5.8% and 8.1% in 1991 and 1992, respectively. All multiply sired pods produced both nonhybrid and hybrid seeds. As many as three successful fathers per pod were identified, but the number of markers limited measuring higher levels of multiple paternity. Most multiply sired pods (≈70%) were filled by nonhybrid seeds plus a single hybrid seed. Ovule position effect within multiply sired pods was inferred from the nonrandom distribution of hybrid seeds within a pod. On average, hybrid seeds occurred more frequently in ovules in position 7 (most basal) and in position 1 (most stylar) than in ovules in the middle positions of the pod.     

Patterns of variation in cultivated common bean (Phaseolus vulgaris,Fabaceae)

More than 18,000 accessions of common bean (Thaseolus vulgaris, Fabaceae) from the Centro Internacional de Agricultura Tropical (CIAT) germplasm bank were examined at two locations in Colombia. A large variation in cultivated dry bean was found among accessions from primary centers of domestication in Middle and South America. For some bean types, such as medium- and large-seeded white, variation was greater among germplasm from western Asia (Turkey) and Europe (Portugal, Spain, Greece, France, Italy, and Bulgaria). Based on growth habit, on seed, pod, and leaf characteristics, and on ecological regions of adaptation, dry-bean germplasm was divided into a total of six gene pools from Middle American and four gene pools from South American centers of domestication. Most of the variation in the snap or stringless bean appears to be of relatively recent origin; it was greatest among cultivars from China, Europe, and the United States. These could be grouped into two additional gene pools. A strategy for breeding and transfer of genes across gene pools is also discussed.     

Anatomical root variations in response to water deficit: wild and domesticated common bean (Phaseolus vulgaris L)

Root anatomical responses to water deficit are diverse and regulation of water uptake strongly depends on plant anatomy. The ancestors of common bean (Phaseolus vulgaris L.) cultivars are the wild common beans. Because wild beans adapt and survive well in the natural environment, it is hypothesized that wild common bean roots are less affected than those of domesticated beans at low substrate water potential (ψW). A wild common bean accession from Chihuahua Mexico and cv. Bayomex were studied. Seedlings with a mean root length between 3 and 4 cm were maintained for 24 h in vermiculite at ψW of -0.03 (well hydrated), -0.65, -1.48 and -2.35 MPa (partially dry). Ten anatomical characteristics of differentiation and cell division in root regions were evaluated. Thickness of epidermis and protoderm diminished similarly in wild and domesticated beans growing at low substrate ψW (between -0.65 and -2.35 MPa). At the same time, parenchymatic cell area diminished by 71 % in the domesticated variety, but by only 32 % in the wild bean at -2.35 MPa. The number of cells in the cortex and the thickness of the xylem wall increased in both wild and domesticated beans at low substrate ψW; nevertheless, the effect was significantly lower in the wild bean. The number of xylem vessels increased in the cultivar (up to 40 %) while in the wild bean it decreased (up to 33 %). The diameter of xylem vessels and transverse root area diminished (15 and 57 %, respectively) in the cultivar, but in the wild common bean were not affected. Anatomical root characteristics and their modifications in both differentiation and cell division in root regions demonstrated that the wild bean reacted quite differently to substrate ψW than the domesticated common bean.     

Purification and characterisation of a novel papain inhibitor from common bean (Phaseolus vulgaris) seed

A proteinaceous inhibitor of papain was purified to apparent homogeneity from mature seeds of common bean ( Phaseolus vulgaris L.). After four chromatographic steps, the papain inhibitor was purified 219‐fold with 12% recovery. On the basis of papain inhibitory activity, cystatins have been estimated to account for about 0.1% of the total protein content of mature common bean seeds. The purified protein, as other plant cystatins, is an acidic protein, heat stable and insensitive to reducing agents. Its molecular mass is about 37 kDa as judged by size exclusion chromatography and SDS‐PAGE. Moreover it is immunologically related to oryzacystatins, since it is recognised by a specific oryzacystatin I antiserum. Based on its biochemical properties the papain inhibitor described here belongs to the phytocystatin family. Papain inhibitory assays carried out during seed development showed that bean cystatin is active since early maturation stages. Our results suggest that, in common bean seed, cysteine proteinase inhibitors are important during seed development with a putative role in the control and regulation of endogenous thiol protease activity.     

Sphingolipids in bean leaves (Phaseolus vulgaris)

Phytoglycolipid has been isolated for the first time from plant leaves (Phaseolus vulgaris). The purified product (almost identical with the phytoglycolipid isolated from flax seed) was a ceramide attached through phosphate diester linkage to an oligosaccharide, which consisted of the usual trisaccharide unit (inositol, hexuronic acid, hexosamine) to which were attached mannose, galactose, and arabinose. The major fatty acids were the saturated 2-hydroxy C(22), C(24), and C(26) acids; the major long-chain bases were dehydrophytosphingosine (d-ribo-1,3,4-trihydroxy-2-amino-8-trans-octadecene) (53%) and phytosphingosine (d-ribo-1,3,4-trihydroxy-2-amino-octadecane) (32%). A ceramide and a cerebroside were also isolated. In the ceramide the major fatty acids and the major long-chain bases were the same as in the phytoglycolipid. In the cerebroside, the fatty acid composition was similar to that in the ceramide and phytoglycolipid, but the long-chain bases consisted of dehydrophytosphingosine and phytosphingosine (7:1) with a substantial amount of unidentified long-chain base. The sugar component was glucose.     

Microsatellite marker diversity in common bean (Phaseolus vulgaris L.)

A diversity survey was used to estimate allelic diversity and heterozygosity of 129 microsatellite markers in a panel of 44 common bean (Phaseolus vulgaris L.) genotypes that have been used as parents of mapping populations. Two types of microsatellites were evaluated, based respectively on gene coding and genomic sequences. Genetic diversity was evaluated by estimating the polymorphism information content (PIC), as well as the distribution and range of alleles sizes. Gene-based microsatellites proved to be less polymorphic than genomic microsatellites in terms of both number of alleles (6.0 vs. 9.2) and PIC values (0.446 vs. 0.594) while greater size differences between the largest and the smallest allele were observed for the genomic microsatellites than for the gene-based microsatellites (31.4 vs. 19.1 bp). Markers that showed a high number of alleles were identified with a maximum of 28 alleles for the marker BMd1. The microsatellites were useful for distinguishing Andean and Mesoamerican genotypes, for uncovering the races within each genepool and for separating wild accessions from cultivars. Greater polymorphism and race structure was found within the Andean gene pool than within the Mesoamerican gene pool and polymorphism rate between genotypes was consistent with genepool and race identity. Comparisons between Andean genotypes had higher polymorphism (53.0%) on average than comparisons among Mesoamerican genotypes (33.4%). Within the Mesoamerican parental combinations, the intra-racial combinations between Mesoamerica and Durango or Jalisco race genotypes showed higher average rates of polymorphism (37.5%) than the within-race combinations between Mesoamerica race genotypes (31.7%). In multiple correspondance analysis we found two principal clusters of genotypes corresponding to the Mesoamerican and Andean gene pools and subgroups representing specific races especially for the Nueva Granada and Peru races of the Andean gene pool. Intra population diversity was higher within the Andean genepool than within the Mesoamerican genepool and this pattern was observed for both gene-based and genomic microsatellites. Furthermore, intra-population diversity within the Andean races (0.356 on average) was higher than within the Mesoamerican races (0.302). Within the Andean gene pool, race Peru had higher diversity compared to race Nueva Granada, while within the Mesoamerican gene pool, the races Durango, Guatemala and Jalisco had comparable levels of diversity which were below that of race Mesoamerica.     

Novel Phaseolin types in wild and cultivated common bean (Phaseolus vulgaris,Fabaceae)

Forty-one wild types and 41 cultivars of common bean (Phaseolus vulgaris) from Meso-and South America were screened for variability of phaseolin seed protein using one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS/PAGE) and two-dimensional isoelectric focusing SDS/PAGE. Wild accessions from the Andean region showed phaseolin types which had not been previously identified in wild material from that region. Other wild accessions from Argentina exhibited novel phaseolin patterns collectively designated as ‘J’ (‘Jujuy’) phaseolin types, and one accession from northern Peru exhibited a novel phaseolin type, the ‘I’ (‘Inca’) type. The ‘H’ and ‘C’ phaseolins, previously identified only in cultivars, were observed in several wild accessions from Argentina. Among cultivars, two minor variants of the ‘S’ phaseolin type were identified. The ‘Sb’ (‘S Brazil’) was characteristic of a limited number of cultivars from Brazil whereas the ‘Sd’ (‘S Durango 222’) predominated in cultivars of the Mexican central highlands. The distribution of the previously described ‘B’ phaseolin appeared to be larger than formerly known as it extended not only in Colombia but also in Central America. It is possible to correlate the ‘Sb’, ‘Sd’, and ‘B’ phaseolin types with certain agronomic traits.     

RFLP diversity of common bean (Phaseolus vulgaris) in its centres of origin.

Eighty-five wild and cultivated accessions of common bean (Phaseolus vulgaris L.), representing a wide geographic area in the centres of domestication were tested for restriction fragment length polymorphisms (RFLPs). Genomic DNA was digested with one of three restriction enzymes (EcoRI, EcoRV, and HindIII) and hybridized to 12 probes distributed throughout the common bean genome. Accessions could be classified into two major groups with a distinct geographical distribution in Middle America and the Andes. Within each gene pool, cultivated accessions clustered together with wild forms from the same geographical area supporting the multiple domestications hypothesis for this crop. Estimates of Nei's genetic distances among the cultivated races from the two different gene pools varied from 0.12 to 0.56 and among races from the same gene pool from 0.04 to 0.12, suggesting that the divergence in Phaseolus vulgaris has reached the subspecies level. The level of genetic diversity (Ht = 0.38) was twice the value obtained with isozyme analysis. Genetic diversity within races (Hs = 0.27) was four to five times higher compared with isozymes, but genetic diversity between races (Dst = 0.11) was similar for both categories of markers. These results corroborate previous studies on the characterization of genetic diversity in common bean that clearly showed two distinct gene pools, Middle American and Andean. Moreover, RFLP markers are superior to isozymes because they provide better coverage of the genome and reveal higher level of polymorphisms.     

Multiple origins of the determinate growth habit in domesticated common bean (Phaseolus vulgaris)

Background and Aims

The actual number of domestications of a crop is one of the key questions in domestication studies. Answers to this question have generally been based on relationships between wild progenitors and domesticated descendants determined with anonymous molecular markers. In this study, this question was investigated by determining the number of instances a domestication phenotype had been selected in a crop species. One of the traits that appeared during domestication of common bean (Phaseolus vulgaris) is determinacy, in which stems end with a terminal inflorescence. It has been shown earlier that a homologue of the arabidopsis TFL1 gene – PvTFL1y – controls determinacy in a naturally occurring variation of common bean.

Methods

Sequence variation was analysed for PvTFL1y in a sample of 46 wild and domesticated accessions that included determinate and indeterminate accessions.

Key Results

Indeterminate types – wild and domesticated – showed only synonymous nucleotide substitutions. Determinate types – observed only among domesticated accessions – showed, in addition to synonymous substitutions, non-synonymous substitutions, indels, a putative intron-splicing failure, a retrotransposon insertion and a deletion of the entire locus. The retrotransposon insertion was observed in 70 % of determinate cultivars, in the Americas and elsewhere. Other determinate mutants had a more restricted distribution in the Americas only, either in the Andean or in the Mesoamerican gene pool of common bean.

Conclusions

Although each of the determinacy haplotypes probably does not represent distinct domestication events, they are consistent with the multiple (seven) domestication pattern in the genus Phaseolus. The predominance of determinacy in the Andean gene pool may reflect domestication of common bean prior to maize introduction in the Andes.     

Nodule conductance varied among common bean (Phaseolus vulgaris) genotypes under phosphorus deficiency

Common bean genotypes BAT477, COCOT, DOR364, Flamingo, and NAG310 were inoculated with Rhizobium tropici CIAT899 and grown under phosphorus deficiency. This treatment induced a significant decrease in shoot and nodule growth that varied among genotypes from 35% to 57% and from 45% to 61%, respectively, whereas root biomass was less affected. Phosphorus deficiency affected differently the genotypes for nodule number and size, and the responses of nodulated-root O2 uptake (Conr) to raising rhizospheric PO2. From the later data, nodule conductance could be computed by dividing the slope of the regression of Conr as a function of external pO2 by nodule surface area. It is concluded that differences in nodule conductance are related to genotypic tolerance to P deficiency.