Guy Mergeai

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.

Development of high-gossypol cotton plants with low-gossypol seeds using trispecies bridge crosses and in vitro culture of seed embryos

The objective of this work is to develop an upland cotton, Gossypium hirsutum L. [2n = 4x =52, 2(AD)h], having a reduced level of gossypol in the seeds for food and feed uses, and a high level of gossypol in the remaining organs to limit pest incidence. Using G. sturtianum Willis (2n = 2x = 26, 2C1) as donor and G. thurberi Torado (2n = 2x = 26, 2D1) or G. raimondii Ulbrich (2n = 2x = 26, 2D5) as bridge species, two trispecies hybrids G. thurberi– G. sturtianum– G. hirsutum and G. hirsutum– G. raimondii– G. sturtianum were synthesized. Both trispecies hybrids were male sterile. Recurrent backcrossing to G. hirsutum as pollinator and selfing of the second backcross (BC) progenies resulted in seeds which were rescued by in vitro culture. In total, 1208 flowers of the trispecies hybrids and their BC progenies yielded 192 seed embryos from which 62 plants were obtained. Cytogenetic analyses indicated a relatively high frequency of chromosome pairing and chiasmata. The gland levels in backcross seeds ranged from glandless seeds to normally glanded seeds. All vegetative parts of those hybrids were glanded, but a wide range of variability for gland density was observed on leaf, stem, bract and calyx. Plants derived from seeds having a reduced level of gossypol constitute very interesting germplasm to develop a cultivated glanded cotton with low-gossypol seeds.

Development of an In vitro pod culture technique for young pods of Phaseolus vulgaris L.

SummaryA research program to develop an in vitro culture technique adapted to very immature Phaseolus zygotic embryos indicated that osmolality within young pods in vivo ranged from 580 to 350 mosm during the first 10 d after pollination. Different culture techniques for 2-d-old Phaseolus pods are described using a modified Phillips medium for maturation. The application of high and variable osmolality conditions, similar to what is observed in vivo, during pod culture (1 wk) and before extracting the embryos, gave the best results in terms of ovule and embryo development. To solve contamination problems affecting pod development during these investigations, a sterilizing technique was tested combining various concentrations of polyoxyethylenesorbitan monolaurate (Tween 20) and a broad-spectrum industrial biocide, Plant Preservative Mixture (PPM). The PPM sterilizing method totally eliminated pod contamination and did not affect ovule growth, but significantly reduced the embryo germination rate.

Identification and characterization of drought stress responsive genes in faba bean (Vicia faba L.) by suppression subtractive hybridization

Faba bean (Vicia faba L.) ranks fourth in food legume crop production in the world. However, drought is a potential major constraint to faba bean production and improved faba bean cultivars and development of drought-resistant varieties play a key role in enhancing faba bean crop production. In this study, suppression subtractive hybridization (SSH) technique was used to study differential expression in response to water stress and to identify genes involved in molecular mechanism of drought tolerance. A forward subtractive cDNA library induced by water deficit conditions was constructed used Hara faba bean cultivar grown in pots and treated with either well-watered (WW) or water-stressed (WS). A total of 28 clones were identified as drought stress induced. After sequencing, ten unique expressed sequence tags (ESTs) were obtained by clustering and blast analysis which showed homology to known drought responsive genes including heat shock protein (HSP), late embryogenic abundant (LEA), zinc finger protein transcription factors (ZFP), lipid transfer protein (LTP), chlorophyll a/b-binding protein (ChlBP), thioredoxin h (Trx h), and ATP synthase as well as some functionally unknown transcripts. Their expression was characterized in Leaf, root, flower, cotyledon, and stem tissue. Quantitative RT-PCR analysis revealed that eight genes were consistently up-regulated in Hara compared to Giza3 cultivar, known as drought-tolerant and sensitive respectively under water deficit treatment. The expression of six genes was differentially expressed in different stages of water stress faba bean plant. Drought responsive genes showed changed expression patterns, indicating that they may play important roles in faba bean water stress response. Furthermore, these results indicate that drought-induced genes are related to metabolic pathways and genetic regulation of stress and development and can serve as a foundation for future studies to elucidate drought stress mechanisms of faba bean.

Insects Associated With Jatropha curcas Linn. (Euphorbiaceae) in West Niger

Abstract Jatropha curcas has been introduced into Niger since 2004 by International Crops Research Institute for the Semi-Arid Tropics (ICRISAT). This plant is cultivated for its oil, which can be used as a Biofuel. Through direct and indirect insect collection methods, an inventory of the insect associated with J. curcas has been conducted in Western Niger during two rainy seasons (from June to October) in 2010 and 2011. We have identified insects belonging to the following families: Acrididae ( Oedaleus senegalensis Krauss , Oedaleus nigeriensis Uvarov, Heteracris leani Uvarov, Catantops stramineus Walker, Parga cyanoptera Uvarov, and Acanthacris ruficornis citrina Audinet-Serville), Pyrgomorphidae ( Poekilocerus bufonius hieroglyphicus Klug), Cetoniidae ( Pachnoda interrupta Olivier, Pachnoda marginata aurantia Herbst, Pachnoda sinuata Heinrich and McClain, and Rhabdotis sobrina Gory and Percheron), Meloidae ( Decapotoma lunata Pallas), Pentatomidae ( Agonoscelis versicoloratus Dallas, Nezara viridula Linn, and Antestia sp. Kirkaldy), Coreidae ( Leptoglossus membranaceus Fabricius and Cletus trigonus Thunberg), and Scutelleridae ( Calidea panaethiopica Kirkaldy). Origin and potential impact on J. curcas of all these insect species are presented and discussed. The lower insect’s diversity indexes are observed in 2010 and 2011 for Niamey, Saga, and Gaya because of semi-arid character of the Sahelian area.

Bridging classical and molecular cytogenetics of Gossypium.

Cotton (Gossypium spp.) is the leading natural fiber crop in the world. The genus Gossypium comprises a broad genetic base that has been and continues to be actively studied by cotton genetists and breeders. Cytogenetic tools play an important role in cotton genome research and cotton breeding. Based essentially on the observation of chromosome morphologies and the analysis of chromosome pairing, classical cytogenetics has contributed greatly to understanding cotton history, taxonomy and phylogeny, and has been a great help in cotton breeding programs designed to transfer desired genes from alien species into cultivated varieties. With the advent of molecular cytogenetics in the 1980s, the field of cytogenetics has been revolutionized. Beside an increase in the speed, sensitivity and specificity of conventional cytogenetic techniques, molecular cytogenetics offers opportunities to perform a variety of tasks not achievable by classical methods. These tasks include analysis of the distribution of repeated sequences along the genome, assignment of repetitive and single copy DNA sequences to positions on chromosomes, determination of the relationship between specific chromosomes and linkage groups, determination of the relationships between physical and genetic distances, differentiation of the genomes involved in hybrids, detection of alien DNA in introgressed lines, and others. We summarize the achievements of classical and molecular cytogenetic investigations in Gossypium and underline the relevance of bridging these approaches in Gossypium genetic studies and exploitation.

Cultural characteristics, pathogenicity and vegetative compatibility of Fusarium udum isolates from pigeonpea (Cajanus cajan (L.) Millsp.) in Kenya

Seventy-nine single-spore isolates of Fusarium udum, the causal agent of wilt disease of pigeonpea, from Kenya, India and Malawi were characterized according to their cultural characteristics, pathogenicity and vegetative compatibility group (VCG). The isolates exhibited high variation in pathogenicity on a wilt-susceptible pigeonpea variety, and in mycelial growth and sporulation on potato dextrose agar medium. The 79 isolates were categorized into two virulence groups, two groups of radial mycelial growth and four groups of sporulation. Radial mycelial growth showed a moderate negative correlation (r = −0.40; P = 0.01) with sporulation. However, mycelial growth and sporulation had no correlation with virulence. Pairings between complementary nitrate non-utilizing (nit) mutants of F. udum generated on chlorate containing minimal medium revealed that all the isolates belonged to a single VCG (VCG 1) with two subgroups, VCG 1 I and VCG 1 II. Vegetative compatibility was independent of cultural characteristics and pathogenicity. This is the first report of vegetative compatibility in F. udum.

Genetic diversity of the african geocarpic legume kersting's groundnut, Macrotyloma geocarpum (Tribe Phaseoleae : Fabaceae)

A survey of allozyme variation in Kerstings groundnut (Macrotyloma geocarpum(Harms) Marechal and Baudet) was undertaken by examining 19 enzymes systems encoding 32 putative loci in 18 domesticated accessions and two wild accessions. No variation was found within and among domesticated accessions as well as within and between both wild accessions. How- ever, very high genetic distance between wild and domesticated accessions suggests that they should be assigned to two different species. 2002 Elsevier Science Ltd. All rights reserved.

Phaseolus Immature Embryo Rescue Technology

Predominant among the production constraints of the common bean Phaseolus vulgaris are infestation of Ascochyta blight, Bean Golden Mosaic virus (BGMV), and Bean Fly. Interbreeding with Phaseolus -coccineus L. and/or Phaseolus polyanthus Greenm has been shown to provide P. vulgaris with greater resistance to these diseases. For interspecific crosses to be successful, it is important to use P. coccineus and P. polyanthus as female parents; this prevents rapid reversal to the recurrent parent P. vulgaris. Although incompatibility barriers are post-zygotic, early hybrid embryo abortion limits the success of F1 crosses. While rescue techniques for globular and early heart-shaped embryos have improved in recent years, -success in hybridization remains very low. In this study, we describe six steps that allowed us to rescue 2-day-old P. vulgaris embryos using a pod culture technique. Our methods consisted of (i) pod culture, (ii) extraction and culture of immature embryos, (iii) dehydration of embryos, (iv) germination of embryos, (v) rooting of developed shoots, and (vi) hardening of plantlets.

Use of randomly amplified polymorphic DNA (RAPD) markers to assist wide hybridization in cotton

In recent years, molecular marker-assisted selection has been integrated into several plant breeding programs to select traits of agronomical importance. Isozymes were initially sought for this purpose, but their use was hindered by the rather small number of loci and alleles available for analysis. The development of molecular biology has resulted in alternative DNA-based procedures for the detection of polymorphism. These include restriction fragment length polymorphism (Tanksley et al. 1989), random amplified polymorphic DNA (Williams et al. 1990), and cleaved amplified polymorphic sequences (Akkaya et al. 1992).