Breeding drought tolerant cowpea: constraints, accomplishments, and future prospects

This review presents an overview of accomplishments on different aspects of cowpea breeding for drought tolerance. Furthermore it provides options to enhance the genetic potential of the crop by minimizing yield loss due to drought stress. Recent efforts have focused on the genetic dissection of drought tolerance through identification of markers defining quantitative trait loci (QTL) with effects on specific traits related to drought tolerance. Others have studied the relationship of the drought response and yield components, morphological traits and physiological parameters. To our knowledge, QTLs with effects on drought tolerance have not yet been identified in cowpea. The main reason is that very few researchers are working on drought tolerance in cowpea. Some other reasons might be related to the complex nature of the drought stress response, and partly to the difficulties associated with reliable and reproducible measurements of a single trait linked to specific molecular markers to be used for marker assisted breeding. Despite the fact that extensive research has been conducted on the screening aspects for drought tolerance in cowpea only very few¿like the `wooden box¿ technique¿have been successfully used to select parental genotypes exhibiting different mechanisms of drought tolerance. Field and pot testing of these genotypes demonstrated a close correspondence between drought tolerance at seedling and reproductive stages. Some researchers selected a variety of candidate genes and used differential screening methods to identify cDNAs from genes that may underlie different drought tolerance pathways in cowpea. Reverse genetic analysis still needs to be done to confirm the functions of these genes in cowpea. Understanding the genetics of drought tolerance and identification of DNA markers linked to QTLs, with a clear path towards localizing chromosomal regions or candidate genes involved in drought tolerance will help cowpea breeders to develop improved varieties that combine drought tolerance with other desired traits using marker assisted selection

Evaluation of Drought Tolerance in Arkansas Cowpea Lines at Seedling Stage

Cowpea [Vigna unguiculate (L.) Walp.] is not only a healthy, nutritious and versatile leguminous crop, it also has a relatively high adaptation to drought. Researches have shown that cowpea lines have a high tolerance to drought, and many of them can survive over 40 days under very hot and dry conditions. The cowpea (Southern pea) breeding program at the University of Arkansas (UA) has been active for over 50 years and has produced more than 1,000 advanced breeding lines. And the purpose of this study is to evaluate the drought-tolerant ability in Arkansas cowpea lines and use the drought tolerant lines in cowpea production or as parents in cowpea breeding. A total of 36 UA breeding lines were used to screen drought tolerance at the seedling stage in this study. The experiment was conducted in greenhouse using completely randomized design (CRD) with two replicates. Drought stress was applied for four weeks, and three drought tolerant related traits were collected and analyzed. Results showed that cowpea breading line: 17-81, 17-86, Early Scarlet, and AR Blackeye #1 were found to be drought tolerant

Resistance to Drought and Salt Stress after Regeneration and Micropropagation.

Investigation was made to confirm the stability of drought and salt stress tolerance in cauliflower (Brassica oleracea var.botrytis) mutants after regeneration and micropropagation. The N-nitroso-N-ethyleurea (NEU) and N-nitroso-N-methylurea (NMU) induced mutants of cauliflower were created and screened for drought and salt stress tolerance. The highly tolerant mutants were selected, regenerated by tissue culture techniques, screened again for drought and salt tolerance under in-vitro and in-vivo conditions, correlated the response of in vitro and in-vivo plants within a clone. Free proline levels in clones were correlated with stress tolerance. Results confirmed the persistence of mutations in clones with enhanced resistance levels to stresses over control plants. The regenerated in-vitro and in-vivo plants within a clone showed a positive significant correlation for drought (R2=0.663) and salt (R2 = 0.647) resistance that confirms the stability of mutation in clones after generations. Proline showed a positive and significant correlation with drought (R2=0.524) and salt (R2 =0.786) tolerance. Conclusively; drought and salt resistance can be successfully enhanced in cauliflower by chemical mutagenesis. Further molecular analysis is recommended to study these mutants

Model assisted phenotyping of processes involved in rice response to drought: case study of a tropical japonica population during vegetative phase : [Abstract, P 7.15]

Tropical japonica rice is frequently exposed to drought in upland ecosystems. Its drought tolerance is poor compared to other crops but the group has great genetic, in part unexploited diversity in adaptations. Exploring the japonica's phenotypic and genetic diversity for drought tolerance is thus crucial to breed rice for drought prone environments. Under such conditions, yield depends on drought timing and intensity along plant phenology. During the vegetative phase, drought affects vigour (leaf number and area, tillering, roots) and therefore resource acquisition. Plant adaptation to drought is a complex mix of physiological tolerance, phenology and morphology, all of which interact with each other and with environment, resulting in phenotypic plasticity. This involves variable regulation of source-sink relationships during morphogenesis (phyllochron, organ expansion, tillering), leaf senescence and transpiration. Studying this system requires dissection into simpler traits involving a smaller number of genes/alleles. However, trait dissection must also account for Genotype*Environment (GxE) interactions and trait plasticity. This is particularly difficult for process based traits that cannot be measured directly. In this context, modelling is relevant if used to dissect a complex system into elemental processes. Each process can be formalized as a response function, with parameters seen as being analogous to genes. The objective of this work is to explore the added value of using dynamic whole plant modelling to assist phenotyping plant response to drought, as a basis for a genetic association study. This work focuses on rice plant transpiration and morphogenesis processes evaluated on seedlings of a diverse sample of tropical japonicas. A greenhouse pot experiment was conducted at Cirad, Montpellier, on 203 japonica accessions with three replications and two treatments (irrigated and drought). Drought was imposed by dry-down from leaf-6 appearance until a targeted stress level was reached, as indicated by Fraction of Transpirable Soil Water (FTSW). FTSW and plant transpiration rates were monitored gravimetrically. At the same time a minimum set of morphological plant descriptors and climate were collected, in order to calibrate, for each genotype and in both well watered and stressed conditions, the corresponding modules of EcoMeristem plant growth model . This paper presents first results and discusses the discriminative power and the added value of model assisted phenotyping for the case of rice drought responses. (Texte intégral

Identification of drought, heat and combined drought and heat tolerant donors in maize (Zea mays L.)

Low maize yields and the impacts of climate change on maize production highlight the need to improve yields in eastern and southern Africa. Climate projections suggest higher temperatures within drought-prone areas. Research in model species suggests that tolerance to combined drought and heat stress is genetically distinct from tolerance to either stress alone, but this has not been confirmed in maize. In this study we evaluated 300 maize inbred lines testcrossed to CML539. Experiments were conducted under optimal conditions, reproductive stage drought stress, heat stress and combined drought and heat stress. Lines with high levels of tolerance to drought and combined drought and heat stress were identified. Significant genotype x trial interaction and very large plot residuals were observed; consequently, the repeatability of individual managed stress trials was low. Tolerance to combined drought and heat stress in maize was genetically distinct from tolerance to individual stresses, and tolerance to either stress alone did not confer tolerance to combined drought and heat stress. This finding has major implications for maize drought breeding. Many current drought donors and key inbreds used in widely-grown African hybrids were susceptible to drought stress at elevated temperatures. Several donors tolerant to drought and combined drought and heat stress, notably La Posta Sequia C7-F64-2-6-2-2 and DTPYC9-F46-1-2-1-2, need to be incorporated into maize breeding pipelines

The genetic basis of drought tolerance in the high oil crop Sesamum indicum

Unlike most of the important food crops, sesame can survive drought but severe and repeated drought episodes, especially occurring during the reproductive stage, significantly curtail the productivity of this high oil crop. Genome‐wide association study was conducted for traits related to drought tolerance using 400 diverse sesame accessions, including landraces and modern cultivars. Ten stable QTLs explaining more than 40% of the phenotypic variation and located on four linkage groups were significantly associated with drought tolerance related traits. Accessions from the tropical area harboured higher numbers of drought tolerance alleles at the peak loci and were found to be more tolerant than those from the northern area, indicating a long‐term genetic adaptation to drought‐prone environments. We found that sesame has already fixed important alleles conferring survival to drought which may explain its relative high drought tolerance. However, most of the alleles crucial for productivity and yield maintenance under drought conditions are far from been fixed. This study also revealed that pyramiding the favourable alleles observed at the peak loci is of high potential for enhancing drought tolerance in sesame. In addition, our results highlighted two important pleiotropic QTLs harbouring known and unreported drought tolerance genes such as SiABI4, SiTTM3, SiGOLS1, SiNIMIN1 and SiSAM. By integrating candidate gene association study, gene expression and transgenic experiments, we demonstrated that SiSAM confers drought tolerance by modulating polyamine levels and ROS homeostasis, and a missense mutation in the coding region partly contributes to the natural variation of drought tolerance in sesame

Update on the search of candidate genes for drought-tolerance in coffee

It is well known that drought periods affect coffee plant development, leading to plant death and abortion of developing fruits in case of severe drought. In relation to coffee genetic diversity, several works reported the identification of plants of C. canephora conilon susceptible or tolerant to drought which were analyzed at the physiological level and also used to identify candidate genes underlying stress responses. Even narrow, a genetic diversity for drought tolerance also exist in the species C. arabica. In addition to the identification of undiscovered transcripts, the recent development of low-cost, high throughput next-generation (NGS) sequencing technologies now opens the way to perform expression profiling and to identify gene presenting differential expression patterns by comparing the frequency of reads obtained after sequencing. In order to initiate such kind of approach in coffee, RNAseq approach was performed using (1) roots of C. canephora conilon susceptible (clone 22) or tolerant (clones 14, 73 and 120) to drought grown under greenhouse conditions with (I) or without (NI) irrigation and (2) meristematic tissues from Iapar59 (I59, drought tolerant) and Rubi (R, drought susceptible) cultivars of C. arabica grown under field-grown with (I) or without (NI) irrigation. These data were compared with those of Coffea transcriptome, including the EST sequences from both C. arabica and C. canephora. Electronic northerns produced by these comparisons identified differentially expressed genes between drought-tolerant and -susceptible clones and cultivars. By qPCR experiments, more than 80 candidate genes, that could play a crucial role in the genetic determinism of drought tolerance in coffee plants, were selected. Based on these results, it can be concluded that the abscisic (ABA) signaling pathway (including ABA synthesis and perception) is one of the major molecular determinants that might explain the better efficiency in controlling stomata closure and transpiration displayed by drought-tolerant clones of C. canephora. The high up-regulation of genes encoding for dehydrins, detoxifying enzymes in drought-tolerant clones of C. canephora also suggests a strong induction of antioxidant and osmoprotection systems in these clones. On the other hand, the over-expression in the plagiotropic meristems of drought-tolerant cultivar IAPAR59 of C. arabica grown under NI of genes coding for proteins involved for example in the SAM (S-adenosyl-methionine) pathway and the wax biosynthesis (i.e. lipid transfer proteins) also suggested their involvement in the genetic determinism of drought tolerance in coffee. Interestingly, our work also led to the identification of several "unknown' (orphan) genes highly over-expressed mainly in droughttolerant plants of both C. canephora and C. arabica. All these RNAseq data are now being analyzed with genomic sequences of drought-susceptible (clone 22) or tolerant (clone 14) of C. canephora for example to see if the differential expression profiles that were observed could be explained by the presence of nucleic polyporphisms (SNPs and/or Indels) in promoter regions of corresponding genes. (Texte intégral

Auxin-sensitive Aux/IAA proteins mediate drought tolerance in Arabidopsis by regulating glucosinolate levels.

A detailed understanding of abiotic stress tolerance in plants is essential to provide food security in the face of increasingly harsh climatic conditions. Glucosinolates (GLSs) are secondary metabolites found in the Brassicaceae that protect plants from herbivory and pathogen attack. Here we report that in Arabidopsis, aliphatic GLS levels are regulated by the auxin-sensitive Aux/IAA repressors IAA5, IAA6, and IAA19. These proteins act in a transcriptional cascade that maintains expression of GLS levels when plants are exposed to drought conditions. Loss of IAA5/6/19 results in reduced GLS levels and decreased drought tolerance. Further, we show that this phenotype is associated with a defect in stomatal regulation. Application of GLS to the iaa5,6,19 mutants restores stomatal regulation and normal drought tolerance. GLS action is dependent on the receptor kinase GHR1, suggesting that GLS may signal via reactive oxygen species. These results provide a novel connection between auxin signaling, GLS levels and drought response

JUNGBRUNNEN1 confers drought tolerance downstream of the HD-Zip I Transcription factor AtHB13

Low water availability is the major environmental factor limiting growth and productivity of plants and crops and is therefore considered of high importance for agriculture affected by climate change. Identifying regulatory components controlling the response and tolerance to drought stress is thus of major importance. The NAC transcription factor (TF) JUNGBRUNNEN1 (JUB1) from Arabidopsis thaliana extends leaf longevity under non-stress growth conditions, lowers cellular hydrogen peroxide (H2O2) level, and enhances tolerance against heat stress and salinity. Here, we additionally find that JUB1 strongly increases tolerance to drought stress in Arabidopsis when expressed from both, a constitutive (CaMV 35S) and an abiotic stress-induced (RD29A) promoter. Employing a yeast one-hybrid screen we identified HD-Zip class I TF AtHB13 as an upstream regulator of JUB1. AtHB13 has previously been reported to act as a positive regulator of drought tolerance. AtHB13 and JUB1 thereby establish a joint drought stress control module.Fil: Ebrahimian Motlagh, Saghar. University of Potsdam; Alemania. Max Planck Institute of Molecular Plant Physiology; AlemaniaFil: Ribone, Pamela Anahí. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Thirumalaikumar, Venkatesh P.. Max Planck Institute of Molecular Plant Physiology; Alemania. University of Potsdam; AlemaniaFil: Allu, Annapurna D.. Max Planck Institute of Molecular Plant Physiology; Alemania. University of Potsdam; AlemaniaFil: Chan, Raquel Lia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Mueller Roeber, Bernd. University of Potsdam; Alemania. Max Planck Institute of Molecular Plant Physiology; AlemaniaFil: Balazadeh, Salma. University of Potsdam; Alemania. Max Planck Institute of Molecular Plant Physiology; Alemani

Drought tolerance of perennial ryegrass (Lolium perenne L.) and the role of Epichloë endophyte : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Manawatu, New Zealand

Perennial ryegrass is the most important grass species in New Zealand. Due to climate change, drought will become more severe and frequent in New Zealand, which makes it increasingly important to improve drought tolerance of perennial ryegrass. There are many ryegrass cultivars in the seed market; however, very limited information is available about drought tolerance of these cultivars. Therefore, the first aim of this thesis was to compare drought tolerance of several market-leading perennial or long-rotation ryegrass cultivars in order to provide cultivar information for pastoral industry. Epichloë festucae var. lolii fungal endophyte naturally colonises perennial ryegrass. Reported effects of endophyte on drought tolerance of the host perennial ryegrass are multifarious. Therefore, the second aim of this thesis was to investigate effects of endophyte on drought tolerance of perennial ryegrass comprehensively. Two main experiments were conducted in this PhD project. In the first experiment, endophyte-free (E–) and endophyte-infected (E+) cloned plants of seven perennial or long-rotation ryegrass cultivars (Grasslands Commando, Ceres One50, Banquet II, Alto, Bealey, Trojan and Avalon), an un-released elite perennial ryegrass line (URL) and one Mediterranean tall fescue cultivar (Grasslands Flecha) were subjected to a cycle of drought and rehydration from December 2012 to May 2013 while other clones of the same plants were irrigated. In the second experiment, two perennial ryegrass cultivars One50 and Commando infected with and without the AR37 endophyte were subjected to a glasshouse experiment. Eight genotypes of each cultivar with and without endophyte infection were either under irrigation or withheld irrigation for two weeks and then rehydrated for one month. A series of plant morphological and physiological responses were measured in each experiment. In the rainout shelter experiment, it was found that Flecha tall fescue was more tolerant to drought than ryegrass cultivars, but this was attributed to its small plant size induced by the partial summer dormancy. Introducing germplasm from Mediterranean areas would be an option to improve drought tolerance of perennial ryegrass in New Zealand. Among evaluated ryegrass cultivars, Banquet II was relatively more drought tolerant than other cultivars, which was also mainly due to its small plant size. In the glasshouse experiment, it was found that Spanish germplasm based One50 was more drought tolerant than „Mangere? ecotype based Commando, suggesting that Spanish germplasm has conferred enhanced drought tolerance to perennial ryegrass in New Zealand. Under both irrigated and non-irrigated conditions, endophyte infection reduced the herbage yield, decreased the relative water content, osmotic potential and stomatal conductance (as indicated by carbon isotope discrimination) and increased the proline concentration of the host compared to E– plants. Also, a majority of these effects were more pronounced in the URL (infected with AR37) and One50 (infected with AR1). It was concluded that E+ plants are at a disadvantage compared to E- plants when insect pressure is artificially controlled, no matter whether the water availability is high or low