M.Sc. (Botany) / Please refer to full text to view abstract

Investigations of three low-water requiring landscape species produced the following results: (1) Although Calliandra californica flowered under photoperiods from 12 to 16 hours, plants produced more elongation under 16 hour days. Plants grew taller and developed greener foliage under irradiances of 600 μmol·m⁻²·s⁻¹. Branching was not stimulated by foliar sprays of BA, PBA, or BA + GA₄₊₇. (2) Caesalpinia pulcherrima increased biomass under 16 hour days, but were stunted and chlorotic under irradiances of 1950 μmol·m⁻²·s⁻¹. Internodal lengths were restricted with drenches of 3.75 mg · pot-1 uniconazole, and plants sprayed with 500 mg·liter⁻¹ PBA developed more axillary branching without negative elongating effects. (3) Justicia specigera gained more height under 12 hour days, and produced greener foliage, more elongation, and faster flowering under irradiances of 600 μmol·m⁻²·s⁻¹. Plants showed restricted internodal elongation and fewer flowers when drenched with 5.0 mg·pot⁻¹ uniconazole, and developed more axillary branching with no detrimental elongation effects when sprayed with 100 mg·liter⁻¹ BA + GA₄₊₇.

Both salinity and drought stresses induce osmotic stress. Thus, cross-tolerance responses and mechanisms may occur in plants. The overall objectives of this study were to determine morphological and physiological responses and mechanisms of turfgrasses and woody species under salinity and drought stress conditions, and determine the relationship between drought and salinity tolerance ability in those species. Five turfgrass entries, ‘Gazelle’ and ‘Matador’ tall fescue (TF), ‘Midnight’ Kentucky bluegrass (KBG), PI368233 (Tolerant KBG), and PI372742 (Susceptible KBG), and three woody species, bigtooth maple (xeric-non saline), bigleaf maple (mesicnon saline) and Eucalyptus (mesic-saline) were compared. For the drought study, water was withheld in Chapter 2 while the dry down treatment was based on daily evapotranspiration (ET) in Chapters 5 and 6. For the salinity study, NaCl and CaCl2 in turfgrasses at electrical conductivity (EC) of 1, 6, 12, 18, and 30 dS m-1 (Chapter 3) and woody species at EC of 1, 3, 6, 9, and 12 dS m-1 (Chapter 4). Susceptible KBG was sensitive to s

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20752号 / 理博第4328号 / 新制||理||1622(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 石田 厚, 教授 工藤 洋, 教授 田村 実 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The Corral de Piedra community is located in Chiquimula, Guatemala. The main agricultural activities are corn and bean production, small-scale gardens, and small animal production, such as poultry and pigs. The crop areas are predominantly located on lands with slopes between 12 and 55%, presenting low fertility conditions and poor moisture retention capabilities. In addition, local crop varieties have low productivity potentials and the winter season is characterized by poorly distributed and erratic periods of rain. The Benson Institute introduced a technology transfer model to increase and diversify agricultural production, while preserving current natural resources. An integral part of this model included educating the community on nutrition and health topics. The school was considered to be the most appropriate place to introduce training and education in agriculture among students and community leaders, thus contributing to community development.

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Peanut (Arachis hypogaea L.) is second major legume crop grown after soybean in the United States, and its productivity is often limited by drought stress. Drought negatively impacts the yield and quality of peanut. Drought stress in peanut causes an annual loss of approximately $520 million in the United States. Improving peanut yield under water deficit conditions is crucial for peanut growers to maintain their profitability in the market. To achieve this, it is essential to either breed or adopt already available drought tolerant cultivars that can produce higher yield under water deficit conditions. Therefore, the objectives of this research were to (1) evaluate five commercially available virginia and runner type peanut cultivars for pod yield stability using multilocation trials by studying G x E interaction across 13 environments including year, location, and irrigation regime. Linn and Binns, AMMI, Shukla, Wricke's, Finlay and Wilkinson stability models were used to determine pod yield stability. Bailey and Sullivan showed higher stability and adaptability across all stability indices whereas Wynne and TUFRunner presented high mean productivity with lesser stability across environments reflecting specific adaptation to just a few environments. Bailey and Sullivan are recommended for sustainable production across the growing region of Virginia and Carolinas. The second objective (2) was identification of drought tolerance related quantitative trait loci (QTL) and genetic markers to facilitate the development of drought tolerant cultivars. Three diverse recombinant inbred line (RIL) populations, derived from crossing lines N05006 x N04074FCT (Pop-1), line N05006 x Phillips, an old virginia-type cultivar (Pop-2), and lines N08086olJCT x PI 585005 (Pop-3) were phenotyped for the Normalized Difference Vegetation Index (NDVI), Canopy Temperature Depression (CTD), SPAD-meter relative chlorophyll content of the leaves (SPAD) and wilting for QTL mapping. Mapping identified 27 minor QTL on eight chromosomes for all physiological characteristics, i.e NDVI, CTD, SPAD and wilting, with logarithmic of odds values ranging from 2.5 to 38.5 and the phenotypic variance explained by these traits from 1.04 to 11.46 %. There were 4 loci on chromosome 2 associated with NDVI in Pop-1 and Pop-3, explaining 1.8 to 10.38% of the phenotypic variation. These genomic regions may be important resources in peanut breeding programs to improve drought tolerance. Further research is needed to increase the marker density in order to fine map the identified QTL and validate markers linked with these regions. / Doctor of Philosophy / Peanut is a multi million-dollar industry in the United States, but water limitations have a detrimental impact on yield, quality, and grower income. Drought along with aflatoxin contamination are two major challenges faced by U.S peanut industry. Annual losses to peanut caused by drought are around $520 million in the United States. Irrigation can alleviate water shortage in drought prone regions, but around 65% of peanut production in U.S is under rainfed condition, meaning that only rainfall can satisfy peanut crop water requirements. The most feasible and economical solution to peanut growers under these circumstances is to adopt drought tolerant varieties. In this research, our goal was to facilitate breeding drought tolerant cultivars through identification of molecular markers associated with drought tolerance and to identify already available drought tolerant peanut cultivars that could be a game changer for the producers. Therefore, the objectives of my research were to (1) evaluate in multiple environments five commercially available virginia and runner type peanut cultivars for pod yield stability and grade factors. In this study, we considered 13 environments, including 4 years, 4 locations, and 2 water regime. Statistical tools including Linn and Binns, AMMI, Shukla, Wricke's, and Finlay and Wilkinson were used to determine pod yield stability. These stability indices showed that Bailey and Sullivan are more stable and adaptable across different locations in terms of yield, whereas Wynne and TUFRunner presented high mean yield with lesser stability showing specific adaptation to only few environments. Based on stability analysis, Bailey and Sullivan are recommended for sustainable production across different growing region of Virginia and Carolinas. The second objective (2) was to identify drought tolerance related genomic regions using three mapping populations. Phenotyping and genotyping of three diverse recombinant inbred line (RIL) populations, derived from crossing lines N05006 x N04074FCT (Pop-1), lines N05006 x Phillips, an old virginia-type cultivar (Pop-2), and lines N08086olJCT x PI 585005 (Pop-3) were done to find quantitative trait loci (QTL) for drought related traits. These population were phenotyped for the Normalized Difference Vegetation Index (NDVI), Canopy Temperature Depression (CTD), SPAD-meter relative chlorophyll content of the leaves (SPAD) and wilting for QTL mapping. These surrogate traits are related to trait of interest for drought tolerance. NDVI is effective in predicting biomass and yield. Similarly, CTD is associated with transpiration efficiency and carbon dioxide assimilation. Mapping identified 27 minor QTL on eight chromosomes for all physiological characteristics, i.e NDVI, CTD, SPAD and wilting with logarithmic of odds values range from 2.5 to 38.5 and the phenotypic variance explained by these traits ranging from 1.04 to 11.46 %. There were 4 loci on chromosome 2 associated with NDVI in Pop-1 and Pop-3, explaining 1.8 to 10.38% of the phenotypic variation. These genomic regions may be important resources in peanut breeding programs to improve drought tolerance. Further research is needed to increase the marker density in order to fine map the identified QTL and validate markers linked with these regions.

Les membranes cellulaires sont des cibles préférentielles de la dégradation induite par les espèces réactives de l’oxygène produites durant la sécheresse et par la stimulation d’activités hydrolytiques. La biosynthèse des lipides des chloroplastes peut être importante pour la tolérance à la sécheresse ainsi que pour la reprise après réhydratation. Dans ce travail nous avons étudié le métabolisme des lipides des membranes chloroplastiques, monogalactosyldiacylglycerol (MGDG), digalactosyl-diacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG), phosphatidyl-glycerol (PG), dans le cadre de la sécheresse et de la reprise après la fin de la contrainte hydrique. Dans ce but, nous avons mesuré la teneur des lipides des feuilles, suivi l’incorporation du précurseur 14C-acétate dans les lipides et analysé l’expression des gènes codant les enzymes de biosynthèse des lipides (MGD1, MGD2, DGD1, DGD2, SQD2 et PGP1) durant le stress hydrique et après réhydratation. Afin de mieux comprendre le rapport entre le métabolisme de ces lipides et la tolérance à la sécheresse, nous avons travaillé sur deux cultivars de Vigna unguiculata L. Walp, un tolérant (cv. EPACE) et l’autre sensible (cv. 1183) à la sécheresse. Les séquences complètes des ADNc des gènes VuMGD1, VuMGD2, VuDGD1, VuDGD2, VuSQD2 et VuPGP1 ont été obtenues par le criblage d’une banque d’ADNc de V.unguiculata. Les résultats montrent qu’en condition de stress hydrique le cultivar tolérant, en plus de préserver la teneur en lipides, est capable de stimuler la biosynthèse du DGDG augmentant significativement le rapport DGDG:MGDG de ces membranes. Nous suggérons que le DGDG accumulé en sécheresse est exporté vers les membranes extrachloroplastiques et que cela contribue à la tolérance à la contrainte hydrique. Les effets de la perte d’eau cellulaire sur les membranes ont des conséquences directes sur la capacité des plantes à reprendre après réhydratation. 48 heures après réarrosage, le cv. sensible 1183 n’est pas capable de récupérer en termes de teneurs en galactolipides et incorporation de précurseur. Chez le cv. tolérant, par contre, la teneur en DGDG demeure élevé, même après réhydratation. En conclusion, nos résultats suggèrent l’importance des lipides membranaires dans la tolérance/sensibilité des plantes au déficit hydrique, en particulier la balance entre des classes lipidiques de propriétés physico-chimiques différentes (SQDG versus PG et DGDG versus MGDG) qui pourraient affecter la structure et le fonctionnement des membranes / Membranes are main targets of degradation by reactive oxygen species and hydrolytic activities induced by drought. Chloroplasts lipid biosynthesis, especially galactolipids monogalactosyl-diacylglycerol (MGDG) and digalactosyl-diacylglycerol (DGDG) are important for plant tolerance to water deficit and for recovery after rehydration. In this thesis, we studied the metabolism of the chloroplast membrane lipids, MGDG, DGDG, sulphoquinovosyl-diacylglycerol (SQDG), phosphatidyl-glycerol (PG) under drought and during recovery from drought. Aiming this, we measured leaf lipids content, followed 14Cacétate incorporation and expression of genes coding for chloroplast membrane lipid synthases (MGD1, MGD2, DGD1, DGD2, SQD2 and PGP1) during drought and recovery. In order to better understand the relationship between drought tolerance and lipid metabolism, two cultivars of Vigna unguiculata L. Walp, one drought tolerant (cv. EPACE) the other drought susceptible (cv. 1183) were compared. The cDNA complete sequences for VuMGD1, VuMGD2, VuDGD1, VuDGD2, VuSQD2 and VuPGP1 were obtained from screening of a V.unguiculata cDNA library. The results showed that under water stress conditions, the tolerant cultivar, besides its ability to preserve its lipids pool despites drought, is able to strongly stimulate the DGDG biosynthesis, increasing the DGDG:MGDG ratio in its membranes. We suggest that DGDG accumulated under drought condition, when phosphate is deficient, is exported for extrachloroplastic membranes, and thus contributes to plant drought tolerance. Effects of loss of water on cell membranes have direct consequences on plant capacity to recover from stress. 48 hours after rewatering, the susceptible cv. 1183 was not able to fully recover from a moderate stress in terms of leaf galactolipid content and acetate incorporation into MGDG. In EPACE-1, MGDG leaf content remained unchanged after rehydration and DGDG remained higher than in the control plants. In conclusion, our results highlight the importance of membrane lipids in plant adaptation to water deficit and in their capacity to recover from stress. Of particular importance is the balance between lipid classes with various physico-chemical properties (SQDG versus PG, DGDG versus MGDG), since they most likely have a profound influence on membrane structure and function

Doctor of Philosophy / Department of Agronomy / P.V. Vara Prasad / The pathway for the movement of water through plants, from the soil matrix to the atmosphere, constitutes the hydraulic architecture of a plant. The linkage between the hydraulic architecture of woody plants and drought tolerance has received considerable attention, but much less work has been done on grasses. I investigated the linkage between the hydraulic architecture of grasses to physiological patterns of water use across a range of species and conditions. The rate of stomatal conductance (g[subscript]s) and photosynthesis (A) increased acropetally along the leaves of 5 grass species, which is a unique feature of this growth form. The internal structure of leaves also changed acropetally in order to minimize the pressure gradient across the mesophyll that would otherwise occur as a result of increasing g[subscript]s. The resistance to water movement through the mesophyll represented 80-90% of leaf resistance in six genotypes of Sorghum bicolor L. (Moench). This resistance was most important in controlling g[subscript]s and A when water was readily available, but as soil-moisture decreased it was the efficient transport of water through the xylem that was most important in maintaining plant function. I also investigated the relationship between hydraulic architecture and stomatal responses of grasses to increasing Vapor Pressure Deficit (D). Grasses with a larger proportion of their hydraulic resistance within the xylem were less sensitive to increasing D and plants with high root conductance maintained higher rates of gas exchange D increased. Finally, I investigated the tolerance of grasses to extreme drought events to test if there was a trade-off between drought tolerance and growth in grasses. Plants with drought tolerant leaf traits typically sacrificed the ability to move water efficiently through their leaves. Having drought tolerant leaves did not limit the plants ability to have high rates of gas exchange, and, in fact, the most drought tolerant plants had the high rates of g[subscript]s when expressed on a mass basis. Leaf-level drought tolerance did contribute to species’ occurrence, as the drought intolerant species I studied are not commonly found in low precipitation systems. The results presented here highlight the importance of studying the hydraulic architecture of plants to provide a better understanding of what controls plant function across a range of environmental conditions.