京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第22782号 / 農博第2425号 / 新制||農||1081(附属図書館) / 学位論文||R2||N5302(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 中村 公人, 教授 星野 敏, 教授 藤原 正幸 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Thesis (M. A. (Agricultural Management)) -- University of Limpopo, 2020 / Field experiments were conducted at two locations; University of Limpopo (Syferkuil) and University of Venda (Thohoyandou) during 2015 and 2016 winter cropping seasons. The objectives of this study were to determine; the effect of genotype (ACC# 1, 3, 4 and 7) and planting density (33, 25 and 20 plants/m2) on four chickpea genotypes having contrasting growth patterns and also to determine the effect genotype and planting density on water use and water use efficiency of four chickpea genotypes having contrasting growth patterns. The experimental design was randomized complete block design in factorial arrangement with three replications. Plant height, number of primary and secondary branches, grain yield and yield components (number of pods per plant, number of seeds per pod, Harvest Index and 100 seed weight [100-SW] and above ground biomass, and were determined at different growth stages. Data obtained was subjected to analyses of variance using the general linear model of Genstat 17th edition. Significant differences between the treatments means were compared using the standard error of difference (LSD) of the means at 5% level. Correlation analyses were performed to assess the relationship between parameters. Plant height varied with genotype from 41 cm (84 DAE) to 44 cm (118 cm) at Syferkuil and 41 (56 DAE) to 44 cm (63 DAE) at Thohoyandou. Primary branches was not significantly affected by genotype and planting density at both locations and seasons. Planting density had significant effect on number of secondary branches, greater number was recorded at low (32, 6) density at Syferkuil in 2016. Above ground biomass was significantly affected by planting density at Syferkuil during in 2015 (5344 kg ha-1) and 2016 (3701 kg ha-1) growing seasons. Genotype and planting density did not affect number of pods plant-1, number of seeds plant-1, 100 SW (100 seed weight), and Harvest index were not significant at both locations and seasons. Grain yield was significantly affected by planting density at Syferkuil in 2015 and Thohoyandou in 2016. Grain yield increased with the increase in planting density at both locations. Two field experiments were conducted at University of Venda (Thohoyandou) during 2015 and 2016 winter cropping seasons. This study aimed at assessing the effect of genotype v and planting density on water use efficiency of four chickpea genotypes with contrasting growth patterns. Crop water use (WU) was determined by monitoring soil water content at 7-day intervals using a neutron probe and, water use efficiency (WUE) was determined as a ratio of crop biomass and grain yield to WU. Genotype and planting density had no significant effect on WU in 2015 and 2016. Genotype and planting density had no significant effect on biomass production (WUEb) and grain yield production (WUEg) in 2015. In contrast, WUEb and WUEg was significantly affected by planting density in 2016. WUEb was 43.2% greater at high density compared to low density. Similarly, WUEg was 39.3% greater at high density compared to low density. WUEb and WUEg increased with the increase with planting density. Therefore, manipulation of management practices such as planting density may increase chickpea production. Keywords: Planting density, genotype, grain yield and yield components, water use efficiency. / National Research Foundation (NRF) and University of Venda Capacity Development

MSCAGR (Plant Production) / Department of Plant Production / Agricultural production under rain-fed conditions is largely dependent on the availability of water stored in the soil during rainfall events. The production of cassava (Manihot esculenta Crantz) under rain-fed conditions in the north-eastern part of South Africa is constrained by low and erratic rainfall events. Improving cassava production in the area requires the use of cassava varieties which are efficient in the use of limited soil moisture. The current climate change and increasing population growth on the planet will place more pressure on agriculture to produce more food using less water. Therefore, previously under-researched and underutilised crop like cassava could be used to bridge the food gap in the future. Although the crop currently occupies low levels of utilisation in South Africa and it is cultivated by smallscale farmers in the Low-veld of Mpumalanga, Limpopo and Kwazulu-Natal provinces using landraces with no improved varieties available in the country. Information on the actual pattern of water extraction, water use and water use efficiency of cassava landraces grown in the dry environments of South Africa is limited. Therefore, the objective of the study was to determine the differences in water use efficiency, gaseous exchange and yield among four cassava landraces grown under rain-fed conditions. Two field experiments were conducted during the wetter (2016/2017) and drier (2017/2018) cropping season at the University of Venda's experimental farm. The trials were laid in a Randomized Complete Block Design (RCBD) consisting of four cassava landraces (ACC#1, ACC#2, ACC#3, and ACC#4) replicated three times. Mature cassava stem cuttings of 30 cm long, were planted manually at a spacing of 1 m x 1 m in both seasons. Each experimental unit consisted of six plant rows of 6 m length (36 m2) and 8 rows of 8 m length (64 m2) in the 2016/17 and 2017/2018 cropping season, respectively. The experiments were under rain-fed conditions without fertilizer additions and the plots were kept weed-free throughout the experimental period. Data collected in the field included soil moisture content, gaseous exchange parameters (net leaf ܥܱଶ uptake, stomatal conductance, and intracellular carbon dioxide concentration), chlorophyll content index (CCI), maximum photochemical quantum yield of PSII (Fv/Fm), effective quantum yield of PSII (ФPSII) and photosynthetic active radiation (PAR). Yield and yield components (root length (cm), root girth (cm), number of storage roots and mean root weight (g plant-1), root yield and aboveground biomass), as well as water use efficiency (WUE), were determined at harvest. Soil moisture content was measured at seven-day interval from sowing until harvest using a neutron probe. Soil moisture data were used to determine crop water use using the water balance approach. There was no variation in the root yield and yield components amongst the landraces in 2017/2018 cropping season but, genotypes affected aboveground biomass, root girth, number of roots per plant and root yield in 2016/2017 cropping season. There was a significant difference (P<0.01) in number of roots (per plant) 81% and 62% greater in ACC#3 and ACC#2 (6.7 & 6.0, respectively) compared with ACC#1 and ACC#4, which both recorded 4 roots per plant. Similarly, root girth was greater in ACC#3 (17.8 cm) and ACC#2 (18.2 cm) compared to ACC#1 (14.1 cm) and ACC#4 (12.9 cm), which were statistically the same. In contrast, total biomass (P<0.01) and root yield (P<0.05) were greater in ACC#3 (20.7 and 11.9 t ha-1, respectively) and ACC#1 (22.0 and 11.3 t ha-1, respectively) compared to ACC#2 and ACC#4 with root yields of 10.2 and 9.5 t ha-1, biomass of 17.1 and 16.3 t ha-1, respectively. Although the genotype x cropping season interaction did not affect root yield and yield components, root yield (by 33.8%; 2.7 t ha-1) and yield components were greater in the wetter compared to the drier season as expected. Water use efficiency of root yield (WUErt) and water use efficiency of biomass production (WUEb) varied with landraces in season I from 37.0 kg ha-1 mm-1 (ACC#4) to 46.60 kg ha-1 mm-1 (ACC#3), and between 71.30 kg ha-1 mm-1 (ACC#2) and 86.0 kg ha-1 mm-1 (ACC#1), respectively. Landraces did not differ in their water use and soil moisture extraction in both seasons but differed in season. However, there was a significant positive correlation between water use efficiency of root yield (WUErt) (0.963***) and water use efficiency of biomass production (WUEb) (0.847***). WUE of biomass production was greater in the drier than the wetter season partly because of dry matter accumulation per evapotranspiration within the landraces. Photosynthesis did not vary with landraces, however, stomatal conductance varied with landraces from 0.08 mmol m-2 s-1 (ACC#4) to 0.2 mmol m-2 s-1 (ACC#2). In contrast, ACC#1 and ACC#3 recorded the same value of stomatal conductance, which is 0.1 mmol m-2 s-1. The effective quantum yield of PSII photochemistry (ΦPSII) did not vary with landraces but the maximum photochemical quantum yield of PSII (Fv/Fm) varied with landraces from 0.652 (ACC#4) to 0.792 (ACC#3) in season II. The proportion of intercepted radiation was affected by landraces in 2017/2018 cropping season. Highest proportion of intercepted radiation was observed in ACC#3 and the lowest in ACC#2. Proportion of intercepted radiation varied with landraces from 22.62% (ACC#2) to 86.45% (#ACC#3). There were significant genotypic variations in chlorophyll content recorded in both season. Chlorophyll content varied with landraces from 33.1 CCI (ACC4) to 55.4 CCI (#ACC3) in the 2016/2017, and in 2017/2018 cropping season chlorophyll content varied with landraces from 36.9 CCI (ACC4) to 78.7 CCI (#ACC3). The highest genotypic variation in chlorophyll content was observed in ACC#3, whilst the lowest chlorophyll content was recorded in ACC#4 in both seasons. / NRF

Drought and salt stress are the main global factors that reduce the average yield of most major crops. In order to meet global demands, we will need to double food production by 2050 (Tilman, Balzer, Hill, & Befort, 2011). Plant growth-promoting bacteria (PGPB) are a group of bacteria that alleviate the harmful effects of abiotic stresses such as salt, heat and drought stress on plants and decrease the global dependence on hazardous agricultural chemicals. We identified that beneficial microbes isolated from desert plants (indigfera argentea) from Jizan region, in 2012 enhance the tolerance of a variety of crop plants to drought and salt stresses under laboratory conditions and in field trials. We analyzed the interaction of these bacteria with the plants by genetic, biochemical and imaging techniques. The goal of this dissertation is to ultimately improve our understanding of the mechanisms of drought and salt stress tolerance conferred by beneficial microbes that can be used as a sustainable solution for plants and crops in degrading lands (deserts) and land affected by abiotic stresses. Outlines how each of chapter of this dissertation will contribute to the discovery of novel drought and salt stress tolerance strategies using a desert-specific bacterial endophyte.

Perennial ryegrass (Lolium perenne L.) is a cool-season turfgrass susceptible to low temperature injury. Wilt-based (WB) irrigation is a common practice in scheduling turf irrigation as an alternative to well-watered (WW). Moisture stress has been shown to promote cold hardiness but this has not been investigated in response to WB irrigation. Measurements of 13C isotope discrimination (DELTA) are useful predictors of water use efficiency (WUE), drought resistance, evapotranspiration (ET) and salinity tolerance but the relevance to turfgrass cold hardiness has not been determined. DELTA analyses may enable more efficient screening protocols in breeding for improved cold hardiness. Objectives of this study were to examine perennial ryegrass genotypes in relation to cold hardiness, DELTA and WUE in response to WW and WB irrigation schedules, to compare genetic diversity between top-performing (TP) and bottom-performing (BP) perennial ryegrass genotypes, and to assess the predictive value of DELTA of for cold hardiness. Six genotypes were selected based on turf quality from the most northern NTEP location (Orono, ME) and included three TP (‘All Star 2’, ‘Mach I’ and ‘Sunkissed’) and three BP (‘APR-1234’, ‘Buccaneer’ and ‘WVPB-R-82’) genotypes. ET, yield, WUE, shoot water content, rooting potential, wilting tendency, DELTA and median lethal temperatures (LT50) using whole-plant survival were measured from greenhouse samples grown in weighing lysimeters in 2007 and 2008. Plant measurements in both years were based on sampling conducted at the last cycle after 68-d of irrigation with 100% of ET applied at leaf-roll (WB) versus ET replacement every 4-d (WW). Lower LT50 values were generally associated with low yield, low WUE and low shoot water content, whether the result of irrigation treatment or genotypic variation. TP genotypes demonstrated significantly lower LT50 temperatures (greater cold hardiness) in comparison to BP genotypes in both years. Modest cold hardiness enhancement with WB irrigation was highest for TP genotypes. Wilting tendency and DELTA were not reliable predictors of cold hardiness, although individual TP genotypes exhibited responses distinctly different than some BP genotypes. Further research is needed to investigate the physiological mechanisms of enhanced turfgrass cold hardiness in response to moisture stress.

No description available.

Drought stress was studied in rice (Oryza sativa) and maize (Zea mays) to identify drought-responsive genes and associated biological processes. One experiment with rice examined drought responses in vegetative and reproductive tissues and identified drought-responsive genes in each tissue type. The results showed that brief periods of acute drought stress at or near anthesis reduced photosynthetic efficiency and ultimately lowered grain yield. Yield was reduced as a result both of fewer spikelets developed and of lower spikelet fertility. Affymetrix arrays were used to analyze global gene expression in the transcriptomes of rice vegetative and reproductive tissue. Comparative analysis of the expressed genes indicated that the vegetative and reproductive tissues responded differently to drought stress. An experiment was conducted with maize, using GS-FLX pyrosequencing to identify differentially expressed genes in vegetative and reproductive tissues; and these results were compared with those from the just-described rice transcriptome. Some of the drought-responsive genes in the maize reproductive tissue were validated by quantitative real time polymerase chain reaction (qRT-PCR). The differentially expressed genes common to both maize and rice were further analyzed by gene ontology analysis to reveal core biological processes involved in drought responses. In both species, drought caused a transition from protein synthesis to degradation, and photosynthesis was one of the most severely affected metabolic pathways. In a validating experiment, a drought-responsive transcription factor found in rice and dubbed HIGHER YIELD RICE (HYR) was constitutively expressed in rice, and the transgenic HYR plants were studied. Under well-watered conditions, the HYR plants developed higher rates of photosynthesis, greater levels of soluble sugars (glucose, fructose, and sucrose), more biomass, and higher yield. They also exhibited a drought-resistant phenotype, with higher water use efficiency, photosynthesis, and relative leaf water content under drought stress. Taken together, these studies demonstrate the potential value of newer technologies for identifying genes that might impart drought resistance and for using such genes to make crops more productive either in the presence or in the absence of drought stress. / Ph. D.

Short rotation woody crops (SRWC) are bred for rapid growth properties. Knowledge of how varying environmental conditions and endophytic bacteria impact physiology are needed to make planting recommendations. Three eastern cottonwood (EC) and three hybrid poplar (HP) varietals were planted in replicate blocks at upland and alluvial sites. Whole-tree water use and water use efficiency (WUE) were measured using heat-dissipation sap flow and related to overall productivity. Productivity measurements were higher at the upland site. Sap flow was higher at the upland site and for endophyte treated individuals. WUE was higher at the alluvial site and for EC. WUE and leaf area index (LAI) were significantly correlated with biomass (negatively and positively respectively). Overall, HP performed better at the upland site, EC at the alluvial site. These results are beneficial in further testing of optimal site and genotype pairings for SRWC.

No description available.

Increasing drought and salinity tolerances in economically important trees adapted to dry land areas is key challenge for maintaining the socioeconomic welfare of dry land areas. Strategies to improve drought and salt tolerance must examine the tree physiological mechanisms that link to the trees survival and growth. This study examined physiological adaptive traits allowing Senegalia senegal to grow better in both saline and dry lands. We conducted two greenhouse experiments and one field study to characterize growth, photosynthetic capacity, water use efficiency (WUE) and gum arabic yield potential among different Senegalia senegal provenances. In the first experiment, we tested early growth and photosynthetic response of seed sources to a cyclic drought treatment. The second greenhouse study examined seed source response to drought, salinity and fertility conditions. Gum yield assessment, growth and WUE of mature trees were determined from a field trial. In general, results showed a high intra genetic variability of Senegalia senegal on gum yield, biomass accumulation and growth. Ngane provenance presented superior growth characteristics as both mature trees and seedlings and exhibited a more conservative water use strategy under drought. Both greenhouse studies revealed similar photosynthetic capacity among Senegalia senegal genotypes when conditions are not limiting. However, when factors such as salinity, fertility and severe drought are involved, different physiological and morphological responses appear and at times this was dependent on seed source. But, at moderate drought stress (chapter 2), no drought by provenance interaction was found. Results of chapter 3 revealed that Ngane has larger stomata with low density in comparison with Diamenar and Kidira provenances. With the exception of Ng21B1, all seed sources displayed similar adaptations to salt stress in term of biomass accumulation. Fertilizer increased total biomass of all seed sources from 63% to 213% for Ng21B1 and K17B19, respectively. However, salinity reduced the fertilizer effect on biomass increment. Leaf gas exchanges were affected by salinity and fertilizer within various responses among seed sources. Results of chapter 4 revealed that gum yield was found to be positively correlated with tree height, crown width, stem volume index and crown area index. Ngane and Diamenar appeared the best provenances in term of annual gum yield per hectare. Diamenar had a higher survival rate than Ngane. This finding reveals the need to consider the tradeoff between tree survival rate and individual tree gum yield in Senegalia senegal stands. In addition to being more sensitive to salinity, Ngane also seems to be more susceptible to low soil pH in terms of survival, but this result needs to be tested further. This study suggests that improvement of gum arabic production can be possible through genetic selection. But, for the best adapted genotypes, research should explore new genetic combination and investigate physiology and genetic diversity. Moreover, the findings on the relationship between soil pH and tree survival rate suggests a need for care in selecting appropriate sites for Senegalia senegal stands. Therefore, silviculture practices as well as genetic selection appear critical in improving gum arabic production. / Ph. D.