Progress 10/01/08 to 09/30/09
Outputs
OUTPUTS: Three experimental systems related to drought tolerance were included in this project. 1) To identify drought tolerance genetic alleles in maize, multi-year/location data for abscisic acid (ABA) and carbohydrate metabolites and single nucleotide polymorphisms (SNPs) from about 500 candidate genes in a diverse population were statistically analyzed (association analysis) using a mixed model with correction for kinship and population structure. 2) To identify physiological processes for maize drought tolerance, four maize hybrids representing extremes in susceptibility/tolerance to drought at flowering were studied in controlled studies in the greenhouse, and several traits were measured, including transpiration, ear and silk growth, water potential, solute potential, and ear metabolites of ABA and carbohydrate. Expression of genes transcripts was profiled in ear tissues using microarray. 3) To identify traits in cassava that underlie differences in drought tolerance, data for several physiological traits from trials in Columbia were analyzed, and ABA and carbohydrate were analyzed in samples from Kenya. PARTICIPANTS: Tim L. Setter (PI/PD) Cornell University; Alfredo Alves (collaborator at CNPMF EMBRAPA) Brazil; Luis Duque (PhD candidate) Cornell University; Martin Fregene (collaborator at CIAT, Columbia); Hernan Ceballos (collaborator at CIAT, Columbia); Jean-Marcel Ribaut (collaborator at GCP); Marilyn Warburton (collaborator at CIMMYT); Jianbing Yan (collaborator at CIMMYT) TARGET AUDIENCES: Researchers involved in genetic improvement and management of crops that are exposed to drought, especially maize and cassava crops. PROJECT MODIFICATIONS: The project will continue in 2010
Impacts
Analysis of trait-SNP associations, corrected for kinship, population structure, and multiple testing, indicated that ABA levels in silks and ears were associated with SNPs in two genes that encode aldehyde oxidases. Phylogenetic analysis indicated the encoded enzymes could be responsible for ABA synthesis, or have multiple substrates/products. Comparative analysis of amino acid sequence in the region surrounding the SNPs, indicated that sequence polymorphisms are in the region of the active site where enzyme kinetics might be determined. Given that ABA accumulation during stress is related to floral and kernel abortion, our identification of these SNP associations provides gene targets for improvement of stress tolerance. In controlled-environment studies of susceptible and tolerant maize hybrids, stress increased levels of ABA and ABA metabolites similarly in all lines, but sucrose levels per g of eartip protein were decreased more in susceptible than tolerant lines. The expression profiles in eartips showed that the susceptible lines had relatively higher transcript levels for stress genes (dehydrins, ethylene metabolism, and stress transcription factors) whereas tolerant lines had higher levels of growth-associated genes. These studies support the idea that better yield performance is related to maintenance of growth-related processes in the face of stress rather than ability to have a high expression of stress-stabilizing gene-products.
Publications
- Ribaut, J.-M., Betran, J. Monneveux, P.,Setter, T. (2009) Drought Tolerance in Maize. p. 311-344 In Handbook of Maize: Its Biology. Bennetzen, J. L. and Hake, S. C (ed.), Springer, New York.
- Setter, T.L., Yan, J., Warburton, M., Buckler, E., Sawkins, M., Ribaut, J.M., Xu, Y., Grudloyma, P., Gethi, J. (2009) Association mapping in maize to improve drought tolerance. In Plant and Animal Genome XVII. www.intl-pag.org, San Diego, p W103
- Yan, J., Setter, T., Buckler, E., Sawkins, M., Xu, Y., Ribaut, J.M., Grudloyma, P., Gethi, J., Gore, M., Warburton, M. (2009) Development of informative markers through association mapping in maize to improve drought tolerance in cereals. P185. In 51st Annual Maize Genetics Conference. Pheasant Run; St. Charles, Illinois, USA, p 135
- Yan, J., Setter, T.L., Warburton, M., Buckler, E.S., Sawkins, M., Ribaut, J.-M., Xu, Y., Grudloyma, P., Gethi, J. (2009) Development of informative markers through association mapping in maize to improve drought tolerance in cereals. In Plant and Animal Genome XVII, San Diego, CA, p P329
|
Progress 10/01/07 to 09/30/08
Outputs
OUTPUTS: This project consists of three sub-projects related to drought tolerance. 1) To identify drought tolerance genetic alleles in maize, we have used an association mapping approach with SNPs identified in candidate genes (500) for drought-related traits. Abscisic acid (ABA) and carbohydrate metabolites were analyzed from samples collected over two years from 384 tropical inbreds in Mexico-TL and from 100 hybrids grown at three locations in the current year. In each case, plants were subjected to water deficit at flowering. 2) To identify physiological processes for maize drought tolerance, eight diverse tropical inbreds were subjected to water stress in a greenhouse during ten-day episodes before pollination. Transpiration, and ear and silk growth were monitored daily. At treatment end we measured leaf water potential, leaf and ear non-structural carbohydrates, ABA, cytokinin, and invertase. 3) To determine the potential for improving drought tolerance of cassava using available diversity for several traits in international germplasm stocks, heritabilities and genotypic correlations with storage root mass were analyzed for the 40+ traits evaluated in a 45-genotype study. Relationships among all phenotyping traits was determined by correlation. PARTICIPANTS: Tim L. Setter (PI/PD) Cornell University; Alfredo Alves (collaborator at CNPMF EMBRAPA) Brazil; Amanda Solliday (MS Candidate) Cornell University; Luis Duque (PhD candidate) Cornell University; Martin Fregene (collaborator at CIAT, Columbia); Hernan Ceballos (collaborator at CIAT, Columbia); Jean-Marcel Ribaut (collaborator at GCP); Marilyn Warburton (collaborator at CIMMYT); Jianbing Yan (collaborator at CIMMYT) TARGET AUDIENCES: Researchers involved in genetic improvement and management of crops that are exposed to drought, especially maize and cassava crops. PROJECT MODIFICATIONS: The project will continue in 2009
Impacts
1) More than 36 single nucleotide polymorphisms (SNPs) from 30 genes were significantly associated with metabolites and field morphological traits. Several ABA metabolite traits were associated with ABA-related genes. Many transcription factors and regulatory proteins were among the significantly associated SNPs. Among agronomic traits, SNP associations with flowering date were abundant. This project provides a short-list of candidate genes for drought tolerance. 2) Processes found in the better maize lines was maintenance of low ear and leaf ABA concentrations and higher sucrose levels in the leaves, more starch in the ear tissue, and relatively little decline in ovary invertase activity. Leaf and ear ABA was negatively correlated with reproductive growth while leaf carbohydrate levels were positively correlated with ear growth, and negatively associated with ABA levels in the leaves and ears. Invertase activity decreased in water-stressed ear tissue compared to control plants. 3) Among diverse cassava lines, high broad sense heritabilities were found in both well watered (WW) and water stress (WS) environments for most traits, including storage root yield and biomass traits, for most morphology and physiology traits, and for leaf ABA; they were lower for leaf carbohydrate contents. Genotypic correlation between storage root mass (Rgy) and harvest index was high, especially in WS, whereas Rgy for shoot biomass was not significant, and it was negative in WS for plant height and fibrous root mass in WW. In WS, Rgy was non-significant for fibrous root mass, suggesting that maintenance of the growth of fibrous roots, which are potentially valuable in accessing deep moisture in the field, was not a penalty while it was in WW conditions. Genotypic ability for leaf retention and chlorophyll was weakly correlated with yield. Canopy temperature indicated that better genotypes had more closed stomata at an early phase of the stress. Rgy for leaf ABA was negative, indicating that better lines accumulated less ABA. Based on this work, we conclude that the best genotypes maintain a robust developmental program that sustains storage root growth in the face of WS, whereas poorer genotypes allow storage root growth to suffer at the expense of other growing plant organs.
Publications
- Alves, A., Dita, M., Silva, A., Oliveira, A. and Setter, T., 2008, Evaluation of drought tolerance in contrasting cassava varieties under a brazilian semi-arid environment. In Proceedings of the First Scientific Meeting of the Global Cassava Partnership (GCP-I), Institute of Plant Biotechnology for Developing Countries (IPBO), Ghent, Belgium, Ghent, Belgium, pp. 149.
- Alves, A., Fregene, M., Setter, T., Duque, L., Ferguson, M. and Mkamilo, G., 2008, Identifying the physiological and genetic traits related to drought tolerance mechanisms in cassava. In Proceedings of the First Scientific Meeting of the Global Cassava Partnership (GCP-I), Institute of Plant Biotechnology for Developing Countries (IPBO), Ghent, Belgium, Ghent, Belgium, pp. 142.
- Duque, L., Setter, T., Ceballos, H., Fregene, M. and Alves, A., 2008, Evaluation of drought tolerance in contrasting cassava varieties genotypes under field controlled water stressed environment. In Proceedings of the First Scientific Meeting of the Global Cassava Partnership (GCP-I), Institute of Plant Biotechnology for Developing Countries (IPBO), Ghent, Belgium, Ghent, Belgium, pp. 143.
- Mutegi, R., Ferguson, M., Maass, B., Mkamilo, G., Kamau, J., Adjebeng-Danquah, J., Alves, A., Setter, T. and Fregene, M., 2008, Field evaluation of cassava varieties under drought stress in Kenya, Tanzania and Ghana. In Proceedings of the First Scientific Meeting of the Global Cassava Partnership (GCP-I), Institute of Plant Biotechnology for Developing Countries (IPBO), Ghent, Belgium, Ghent, Belgium, pp. 148.
- Setter, T., 2008, Association mapping in maize to improve drought tolerance. In Generation Challenge Programme 2008 Annual Research Meeting, www.generationcp.org, Bangkok, Thailand.
- Setter, T., Duque, L. and Alves, A., 2008, Drought tolerance mechanisms in cassava. In Proceedings of the First Scientific Meeting of the Global Cassava Partnership (GCP-I), Institute of Plant Biotechnology for Developing Countries (IPBO), Ghent, Belgium, Ghent, Belgium, pp. 148.
- Solliday AJ. 2008. Identifying favorable responses to drought stress in diverse genotypes of maize (Zea mays L). M.S. thesis. Cornell University, Ithaca, New York, USA. 70 pp.
|
Progress 10/01/06 to 09/30/07
Outputs
OUTPUTS: In collaboration with CIAT, we have completed two years of field trials in Columbia to identify physiological traits among diverse cassava lines (15 lines in the first year and 45 lines in the second year) that are most directly related to genotypic yield performance in drought. Our goal is to determine which traits are responsible for drought tolerance in cassava, so that we can 1) guide future breeding programs in their choice of germplasm, management of drought imposition in field phenotyping, and interpretation of field trials, and 2) develop a short-list of traits that we can use in phenotyping large populations for QTL identification. We have obtained detailed time-series data on a wide range of traits, including fine- and storage-root growth, stomatal conductance, RWC, leaf retention, leaf senescence, carbohydrate storage in stems and leaves, carbohydrate and ABA accumulation in several plant parts. Studies have been conducted in several phenotyping environments:
field trials +/- irrigation at sites with a dry climate, plants grown in pots that exclude soil water and precipitation, and screenhouse trials where rainfall is excluded.
PARTICIPANTS: Tim L. Setter (PI/PD) Cornell University; Luis Duque (PhD candidate) Cornell University; Martin Fregene (collaborator at CIAT, Columbia); Hernan Ceballos (collaborator at CIAT, Columbia); Jean-Marcel Ribaut (collaborator at GCP); Marilyn Warburton (collaborator at CIMMYT); Yunbi Xu (collaborator at CIMMYT)
TARGET AUDIENCES: Researchers involved in genetic improvement and management of crops that are exposed to drought, especially maize and cassava crops.
PROJECT MODIFICATIONS: The project will continue in 2008
Impacts
In collaboration with CIMMYT, we have analyzed several carbohydrate and ABA phytohormone metabolites in maize genotypes. The objective is to identify traits that are associated with maize tolerance to water deficit at flowering, and in turn to use a genetic association approach to identify genes involved in affecting these traits. We have analyzed the level of carbohydrate and ABA metabolites in over 10k samples from leaves, ear-shoots, and silks of 400 maize genotypes grown in well-watered and water deficit conditions. To accomplish this work we developed methods to perform high throughput analysis of ABA metabolites, that complement procedures for ABA that we previously established. For both ears and silks, ABA and ABA metabolites are consistently negatively correlated with ear and silk size and growth. This is in accord with the hypothesis that genotypes which avoid excess ABA synthesis are more successful in sustaining ear and silk growth during stress. For both
ears and silks, there was a negative correlation between ear or silk size (and growth rate) and sugar levels. This suggests that ear and silk growth was not determined by availability of sugar for osmotic adjustment or metabolic/respiratory demands; rather, it suggests that genotypes with better growth do so by regulating other growth-determining processes (possibly by accumulating inorganic solutes to sustain turgor), and allowing their tissue sugar levels to decline. In addition to sugar contents per se, the fraction of sugar in the form of sucrose was negatively related to ear and silk size and growth. This suggests that growth sustaining genotypes can sustain invertase activity to convert sucrose to hexoses. For silks and leaves, ABA levels declined from 0 to 7 days after anthesis; but ABA metabolites increased. This is consistent with the idea that the catabolites of ABA accumulate with time and can be used as a time-integrated measure of ABA synthesis in a genotype.
Publications
- Eom, S.H., Setter, T.L., DiTommaso, A., Weston, L.A. 2007. Differential growth response to salt stress among selected ornamentals. Journal of Plant Nutrition 30: 1109-1126.
- Setter, T.L. and Fregene, M.A. 2007. Recent advances in molecular breeding of cassava for improved drought tolerance. Chapter 28, pp 701-711 In: Jenks, M.A., Hasegawa, P.M., Jain, S.M. (eds), Advances in Molecular-Breeding Toward Drought and Salt Tolerant Crops. Springer, New York
- Ribaut, J.M., Betran, J., Monneveux, P., Setter, T.L. 2008. Drought tolerance in maize. Chaper 14 In: J. Bennetzen and S. Hake (eds) The Maize Handbook, Springer, NY (in press)
- Kurai, T. 2007. Trehalose transgenic lines in Oryza sativa L. have altered carbohydrate partitioning and utilization in response to water deficit and recovery. M.S. Thesis, Cornell University, Ithaca, NY
|
Progress 01/01/06 to 12/31/06
Outputs
In previous studies of cassava conducted 2005, we found evidence for a substantial pool of total non-structural carbohydrate (TNC) reserves in the stem, which was gradually diminished during stress. We hypothesized that these reserves may play an important role in sustaining meristems and other respiring organs during a prolonged stress so that regrowth upon resumed rainfall can be rapid. We also found that root growth was drastically inhibited during stress. To determine whether genotypes differ in these and other stress tolerance traits, in the current reporting period we compared 15 cassava genotypes, differing in stress tolerance, in a screenhouse study. Plants were grown in 1-m tall pots with well-watered and water stress treatments. Plant parts were sampled fives times during a 60-d stress period, to monitor root, leaf and stem growth and relative water content (RWC). Genotypes differed significantly in growth and partitioning of dry matter; however, RWC
remained high throughout the stress period for all genotypes. Among this material, all genotypes displayed pronounced drought avoidance by closing stomata and limiting water use. Genotypes significantly differed in leaf retention during stress. Samples were obtained for abscisic acid, sugars, starch, and root morphology, which will be used to assess genotypic differences in stress response, carbohydrate storage/remobilization, and alterations in root architecture
Impacts
The goal of this project is to elucidate the mechanisms of drought tolerance used by cassava, a crop of high yield potential in favorable environments, and of remarkable maintenance of yield in drought environments. The knowledge gained by this work will provide focus and guide the genetic improvement of cassava and other crops.
Publications
- Duque, L.O. 2006. Response of cassava (Mannihot esculenta, Crantz) to terminal water stress: ABA, sugar and starch accumulation/partitioning and root growth under different water regime treatments. M.S. Thesis, Cornell University, Ithaca, New York.
- Setter, T.L. and Fregene, M.A. 2007. Recent advances in molecular breeding of cassava for improved drought tolerance. In: Jenks, M.A., Hasegawa, P.M., Jain, S.M. (eds), Advances in Molecular-Breeding Toward Drought and Salt Tolerant Crops. Springer, New York
|
Progress 01/01/05 to 12/31/05
Outputs
Cassava is an important staple crop for developing regions worldwide and is valued for its reliable yield in environments subject to abiotic stresses. Although cassava is one of the best crops for drought-prone environments it is also among the most productive crops in well-watered situations. Our objective was to evaluate mechanisms it uses to regulate growth and carbohydrate partitioning during stress. Cassava plants were grown in one meter high pots and were subjected to four different water regimes in the range from -0.38 to -0.59 MPa (initial soil water potential) over a 30-d period. Stomatal conductance, ABA concentrations, and growth responded substantially to all three stress conditions, indicating they were highly sensitive to mild stress. Leaf abscission was severe, and leaf growth decreased but a low rate of new leaf growth was maintained. Main root elongation was not decreased by stress, but the growth of fibrous lateral roots, as reflected in their volume
and DW, was drastically impaired by water stress treatments. In leaf blades and petioles, sugars were the predominant form of nonstructural carbohydrate, while about one third was in starch, and these reserves were depleted rather rapidly during stress. In contrast, stems and storage roots maintained relatively high starch concentrations and contents per organ from treatment initiation to the final harvest. Total nonstructural carbohydrate (TNC) content per plant was maintained in storage roots through the entirety of the experiment, while stem, which constitutes a storage organ for starch during non-stress conditions, became a source of slowly remobilized starch during stress. The amount of starch stored in stems was considerable, representing about 35 percent of the TNC in the plant at T0, and 6 percent of total plant dry mass. We suggest that this pool of TNC reserves is important in sustaining meristems and other respiring organs during a prolonged stress so that regrowth upon
resumed rainfall can be rapid.
Impacts
The goal of this project is to elucidate the mechanisms of drought tolerance used by cassava, a crop of high yield potential in favorable environments, and of remarkable maintenance of yield in drought environments. The knowledge gained by this work will provide focus and guide the genetic improvement of cassava and other crops.
Publications
- Duque, L.O. and Setter, T.L. 2005. Response of cassava (Mannihot esculenta, Crantz) to terminal water stress: ABA, sugar and starch accumulation/partitioning and root growth under different water regime treatments. L 5.09, Interdrought II, The 2nd International Conference on Integrated Approaches to Sustain and Improve Plant Production Under Drought Stress, September 24 to 28, 2005, Rome, Italy
|
|