Jean-Pierre Baudoin

Genetic Diversity In Lima Bean (Phaseolus Lunatus L) As Revealed By Rapd Markers

The genetic variability of 46 accessions of the Lima bean (P. lunatus L.) including 16 wild forms and 30 landraces belonging to the three cultigroups Big lima, Sieva, Potato, and their intermediates, was evaluated using RAPD (Random amplified polymorphic DNA) markers. Twelve oligonucleotide primers produced 172 RAPD markers which allowed the differentiation of two main groups: the mesoamerican and the andean groups. This was confirmed by an AMOVA analysis which indicated that 37.7% of the variation was found between these two groups. For each botanical form (wild and cultivated), the molecular markers showed that small-seeded types (i.e. Sieva and Potato types and their related wild forms) had a wide distribution (from Mexico to Argentina) while the large-seeded types (Big lima type and its related wild forms) were circumscribed to the narrow west-coastal region from Ecuador to Bolivia. The results are in favour of an independent domestication process within the two groups, as the differentiation between mesoamerican and andean accessions was found to occur in both wild forms and landraces. Within each of the two main groups, wild forms and landraces were also found to be genetically differentiated and higher genetic diversity was observed among landraces than among wild forms. Within the mesoamerican landraces, low but significant differentiation between the Sieva and Potato cultigroups was observed. Some suggestions and hypotheses are discussed about evolution of the two small-seeded types.

Genetic structure of a Lima bean base collection using allozyme markers

Abstract Genetic diversity and structure within a Lima bean (Phaseolus lunatus L.) base collection have been evaluated using allozyme markers. The results obtained from the analysis of wild and cultivated accessions confirm the existence of Andean and Mesoamerican gene pools characterised by specific alleles. Wild and cultivated accessions of the same gene pool are grouped. The Andean natural populations have a very limited geographic distribution between Ecuador and northern Peru. The Mesoamerican wild form extends from Mexico up to Argentina through the eastern side of the Andes. Andean and Mesoamerican cultivated accessions of pantropical distribution contribute substantially to the genetic diversity of the Lima bean base collection. Population genetic parameters, estimated from allozymes, confirmed the predominant selfing mating system of the Lima bean. The selfing mating system, the occurrence of small populations, and low gene flow lead to an interpopulation gene diversity (DST=0.235) higher than the intrapopulation gene diversity (HS=0.032). On the basis of the results, guidelines are given to preserve and exploit the genetic diversity of this threatened species. The results also confirm the independent domestication of the Lima bean in at least two centres, one of which is located at medium elevation in the western valleys of Ecuador and northern Peru.

Soil seed bank and seed dormancy in wild populations of lima bean (Fabaceae): considerations for in situ and ex situ conservation

Seed dormancy and its impact on the soil seed bank for wild Lima bean (Phaseolus lunatus) populations were studied in the Central Valley of Costa Rica. Five populations were selected in contrasted environments. In all cases, distribution of seeds in the soil was limited to 3 cm depth. No innate dormancy was observed but combination of hard seed coat and hilum opening controlled by environmental conditions were responsible for an induced dormancy and the constitution of a persistent seed bank. Breaking of this dormancy was obtained by a brief elevation of temperature from 25° to 45°C. Impacts of this phenomenon concern both genetic and demographic aspects of in situ conservation of the species. Consequences on ex situ conservation are mainly related with the regeneration of the seed collection.

Use of chloroplast DNA polymorphisms for the phylogenetic study of seven Phaseolus taxa including P. vulgaris and P. coccineus.

The genetic variability of seven Phaseolus taxa has been evaluated on the basis of molecular data and the results have used to clarify the phyletic relationships between several taxa of the P. coccineus L. complex. Chloroplast DNA (cpDNA) from 33 populations was digested with six restriction endonucleases, revealing some polymorphisms that made it possible to divide most of the taxa into two main groups: the subspecies of P. coccineus on the one hand, and P. vulgaris L., P. polyanthus Greenman and P. costaricensis (Freytag and Debouck) on the other hand. P. polyanthus is closer to P. vulgaris than the other taxa of the second group and should be considered as a separate species. The position of the wild species P. costaricensis is intermediate between P. coccineus and P. polyanthus. P. glabellus shows sufficient polymorphisms at the cpDNA level to be recognized as a separate species, as previously suggested from total seed-protein electrophoretic studies. These results favour the hypothesis of a common phylogeny for P. vulgaris, P. polyanthus, P. costaricensis and P. coccineus from a single wild ancestor. Although cpDNA is generally known to be uniform at the intraspecific level, some additional polymorphisms were also detected within P. vulgaris, P. polyanthus and P. coccineus. Further studies are required to understand the significance of the latter.

Molecular evidence for an Andean origin and a secondary gene pool for the Lima bean ( Phaseolus lunatus L.) using chloroplast DNA

Abstract Chloroplast DNA (cpDNA) diversity has been examined using PCR-RFLP and RFLP strategies for phylogenetic studies in the genus Phaseolus. Twenty-two species, including 4 of the 5 cultivated species (P. lunatus L., the Lima bean; P. vulgaris L., the common bean; P. coccineus L., the runner bean and P. polyanthus Greenman, the year-bean), represented by 86 accessions were included in the study. Six PCR primers designed from cpDNA and a total cpDNA probe were used for generating markers. Phylogenetic reconstruction using both Wagner parsimony and the neighbor-joining method was applied to the restriction fragment data obtained from each of the molecular approaches. P. vulgaris L. was shown to separate with several species of largely Mesoamerican distribution, including P. coccineus L. and P. polyanthus Greenman, whereas P. lunatus L. forms a complex with 3 Andean species (P. pachyrrhizoides Harms, P. augusti Harms and P. bolivianus Piper) co-evolving with a set of companion species with a Mesoamerican distribution. Andean forms of the Lima bean are found to be more closely related to the 3 Andean wild species than its Mesoamerican forms. An Andean origin of the Lima bean and a double derivative process during the evolution of P. lunatus are suggested. The 3 Andean species are proposed to constitute the secondary gene pool of P. lunatus, while its companion allies of Mesoamerican distribution can be considered as members of its tertiary gene pool. On the basis of these data, an overview on the evolution of the genus Phaseolus is also discussed.

Breeding for "low-gossypol seed and high-gossypol plants" in upland cotton. Analysis of tri-species hybrids and backcross progenies using AFLPs and mapped RFLPs.

Abstract This work aims at breeding upland cotton [Gossypium hirsutum L., 2(AD)1 genome] with a reduced level of gossypol in the seeds for optimal food and feed uses, and a high gossypol level in the remaining organs for resistance to pests. Two tri-species Gossypium hybrids, (G. thurberi–G. sturtianum–G. hirsutum and G. hirsutum–G. raimondii–G. sturtianum) including G. sturtianum (2C1) as a donor, G. thurberi (2D1) and G. raimondii (2D5) as a bridge species, were created. Recurrent selection initiated with these tri-species hybrids produced backcross (BC) progenies expressing the ”low-gossypol seed and high-gossypol plant” trait at different levels. We used AFLP markers to assess the genetic similarity among the germplasm and RFLP probes to tag the introgression of specific chomosome segments from the parental species. Five pairs of AFLP primers generated 477 fragments, among which 417 (87.4%) were polymorphic. The genetic similarity between the upland cotton and the wild species ranged from 29.5 to 43.2%, while similarity reached 80% between upland cotton and BC3 plants. Introgression of species-specific AFLPs was evident from all the parental species and confirmed the hybrid origin of the analyzed progenies. Southern-blot analysis based on 49 RFLP probes allowed us to trace the introgression of parental DNA segments in the tri-species hybrids and in three generations of backcross. Introgression was evident from 11, 8 and 7 linkage groups of G. sturtianum, G. raimondii and G. thurberi respectively. The types of introgression revealed by RFLP probes are discussed, and breeding schemes to enhance recombination are proposed. The ability to trace DNA segments of known chromosomal locations from the donor G. sturtianum through segregating generations is a starting point to map the ”low-gossypol seed and high-gossypol plant” traits.

Reproductive biology of the andromonoecious Cucumis melo subsp agrestis (Cucurbitaceae)

BACKGROUND AND AIMS Cucumis melo subsp. agrestis (Cucurbitaceae) is cultivated in many African regions for its edible kernels used as a soup thickener. The plant, an annual, andromonoecious, trailing-vine species, is of high social, cultural and economic value for local communities. In order to improve the yield of this crop, the first step and our aim were to elucidate its breeding system. METHODS Eight experimental pollination treatments were performed during three growing seasons to assess spontaneous selfing, self-compatibility and effects of pollen source (hermaphroditic vs. male flowers). Pollination success was determined by pollen tube growth and reproductive success was assessed by fruit, seed and seedling numbers and characteristics. The pollinator guild was surveyed and the pollination distance determined both by direct observations and by indirect fluorescent dye dispersal. KEY RESULTS The species is probably pollinated by several Hymenoptera, principally by Hypotrigona para. Pollinator flight distances varied from 25 to 69 cm. No evidence for apomixis or spontaneous self-pollination in the absence of insect visitors was found. The self-fertility index (SFI = 0) indicated a total dependence on pollinators for reproductive success. The effects of hand pollination on fruit set, seed number and seedling fitness differed among years. Pollen tube growth and reproductive success did not differ between self- and cross-pollinations. Accordingly, a high self-compatibility index for the fruit set (SCI = 1.00) and the seed number (SCI = 0.98) and a low inbreeding depression at all developmental stages (cumulative delta = 0.126) suggest a high selfing ability. Finally, pollen origin had no effect on fruit and seed sets. CONCLUSIONS This andromonoecious species has the potential for a mixed mating system with high dependence on insect-mediated pollination. The selfing rate through geitonogamy should be important.

Population Genetic Structure Of Wild Phaseolus Lunatus (Fabaceae), With Special Reference To Population Sizes

To set up an in situ conservation strategy for Phaseolus lunatus, we analyzed the genetic structure of 29 populations in the Central Valley of Costa Rica. Using 22 enzyme loci, we quantified the proportion of polymorphic loci (P(p)), the mean number of alleles per locus (A), and the mean effective number of alleles per locus (A(e)), which equaled to 10.32%, 1.10, and 1.05, respectively. The total heterozygosity (H(T)), the intrapopulation genetic diversity (H(S)), and the interpopulation genetic diversity (D(ST)) were 0.193, 0.082, and 0.111, respectively. The genotypic composition of the analyzed populations showed a deviation from the Hardy-Weinberg proportions (F(IT) = 0.932). This disequilibrium was due to either genetic differentiation between populations (F(ST) = 0.497) or nonrandom mating within populations (F(IS) = 0.866). From the level of genetic differentiation between populations and the private alleles frequencies estimates, gene flow was calculated: Nm(W) = 0.398 and Nm(S) = 0.023, respectively. The results suggested that wild Lima bean maintains most of its isozyme variation among populations. Significant positive correlation was observed between population size and P(p), A, and H(o) (observed heterozygosity), whereas no correlation was observed with the average fixation index of population (F). The loss of genetic variability in populations was attributed to inbreeding and the bottleneck effects that characterized the target populations. In situ conservation and management procedures for wild Lima bean are discussed.

Genetic Diversity In The Lima Bean (Phaseolus Lunatus L.) As Revealed By Chloroplast Dna (Cpdna) Variations

Genetic diversity in the Lima bean (P. lunatus L.) was assessed bymeans of two chloroplast DNA probes. Based on data obtained from 152accessions including wild forms and landraces, the two separateMesoamerican and Andean groups were confirmed and a transition poolof genetic diversity was observed in the two botanical formsconsistent with their distribution range. Three primary centres ofgenetic diversity and one secondary diversification spot are proposedfor the wild Lima bean whereas only two domestication sites areunderlined for the landraces. The importance of human intervention inwidening the distribution range and the genetic diversity inlandraces is discussed.

Role of myo-inositol phosphate synthase and sucrose synthase genes in plant seed development

The aim of this review is to highlight the role of myo-inositol phosphate synthase (MIPS), which catalyses the first step in inositol biosynthesis and of sucrose synthase (Sus), an enzyme involved in UDP-glucose formation, the principal nucleoside diphosphate in the sucrose cleavage reaction and in trehalose biosynthesis. These two enzymes are involved in various physiological processes including seed growth and resistance to biotic and abiotic stresses. The study of mutated MIPS and Sus genes in some crops, such as soybean and cotton, has shown that these two proteins are directly involved in embryogenesis. They exhibit several isoforms that are essential for normal seed development. The possible role of both genes in seed development is discussed in this review.