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Item Water-use efficiency in perennial ryegrass (Lolium perenne L.) : 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(Massey University, 2021) Weerarathne, Lekamalage Visna YahaniKnowledge of genetic and physiological bases of drought responses and stress tolerance properties of pasture plants is an integral part of designing efficient pasture improvement programs to combat the consequences of climate change. However, experimental evidence or theoretical analyses on that aspect is sparse in the literature. Therefore, considering wider applications, high economic importance, and acknowledged poor tolerance of (Lolium perenne L.; PRG) to drought, the main aim of this research was to evaluate morpho-physiological trait responses that are linked to water-use efficiency (WUE) in different PRG populations from different sources in simulated summer drought cycles under a controlled environment. This study also included a quantitative genetic analysis conducted on the key traits to ascertain which traits are under genetic control for future breeding purposes. Experiment 1 screened single potted PRG genotypes from three commercial cultivars with industry reputation for persistence for natural differences in morpho-physiological traits related to water use (WU) under simulated drought. Large within-population variation was observed for the measured traits which included, among others, WUE (g WU/g plant dry matter); shoot dry weight, SDW; leaf osmotic potential, OP; leaf relative water content; predawn leaf water potential; root dry weight at 20–50 cm depth, RDWD; gravimetric soil moisture at 30–40 cm depth, SMCD; post-cutting regrowth. Principal component analysis (PCA) identified important trait associations contributing to high WUE (i.e. WUE-OP-RDWD trait association) and one related to higher SDW together with ‘SMCD conservation’ indicative of ‘true WUE’ was used to make a divergent selection of 20 high- and 15 low-WUE genotypes (HWUE and LWUE, respectively). Experiments 2 and 3 were conducted simultaneously using the same methodology as Experiment 1 and inter-randomised in the same glasshouse space. Experiment 2 retested clones of HWUE and LWUE plants selected in Experiment 1 for consistency of trait expression across the two consecutive growing seasons, and also collected data for additional traits. Results confirmed that the key trait associations identified in Experiment 1 were almost identically expressed in Experiment 2. From data on additional traits, it was established that the accumulation of high molecular weight sugars in the shoots significantly contribute to ‘true WUE’ of a subset of PRG genotypes but, with the less involvement of gas exchange data under the conditions tested. It is speculated that enhanced mesophyll conductance of CO2 might underlie this important trait association. However, the large majority of genotypes exhibited a ‘SMCD-depleting’ trait association of WUE with improved gas exchange and maximum quantum efficiency of PSII, demonstrating late A.R. Blum’s theory of WUE. Thus, selection of PRG for drought tolerance should consider yield and soil moisture data together to establish the most appropriate category of WUE trait association in improved cultivars. Experiment 3 investigated drought response trait associations in two further populations: a group of elite plants from a commercial plant breeder’s breeding program (CBL) and a PRG germplasm line derived from crossing Mediterranean and Middle Eastern seed accessions (MMEL) compared with those from the HWUE selection. PCA results showed that the major trait associations found in the yield and water relations data of elite subsets of CBL closely followed those of the HWUE selection, but elite MMEL plants exhibited typical summer dormancy characteristics where the average SDW of MMEL was 40% of lower than that of the CBL plants. Results further suggested that the company field evaluation system could benefit from the consideration of water relations traits, including WUE and associated traits like OP, as externally-measured selection traits for PRG drought tolerance. Experiment 4 evaluated quantitative genetic parameters of the key traits using the same methodology from Experiment 1 in a breeding population of 36 ‘half-sib (HS) families’ under both stressed and non-stressed conditions. There were significant estimates of among- and within-HS family genetic variances, narrow-sense heritability, and predicted genetic gain estimates for the key traits, indicating high genetic potential of each trait for breeding purposes under the conditions tested. However, the correlated response to selection of each trait pair comprising highly genetically correlated morpho-physiological traits with WUE was lower than that gain from the single-trait selection, accommodating further research questions on the efficacy of indirect and multi-trait selection of key traits. Based on the current results, it was found that the direct selection of PRG for WUE or concurrent selection for OP, RDWD, SMCD, and SDW or RGS traits under drought is advisable. Furthermore, significant quantitative genetic parameters estimated for WUE under non-stressed conditions together with high genetic correlation observed for WUE between stressed and non-stressed conditions suggested that a PRG population can potentially be selected for this trait at early growth stages or before imposition of water deficit.Item Coupled effects of irrigation management and water salinity on date palm cultivars in the hyper-arid environment of the United Arab Emirates : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Soil and Environment Sciences, School of Agriculture and Environment, Massey University, Palmerston North, New Zealand(Massey University, 2019) Al Muaini, Ahmed HassanDates, and the farming of date palms (Phoenix dactylifera L.), are culturally, aesthetically and economically important in the United Arab Emirates. In this hyper-arid region, dates require irrigation, as rainfall is virtually non-existent. Groundwater is relied upon as the source of this irrigation water. Yet, the groundwater reserves in the Emirates are expected to run-out in about 55 years. Furthermore they are becoming more saline. In the Emirate of Abu Dhabi, Law 5 has been passed and that will limit the amount of water that can be withdrawn for agriculture, or any other purposes. Thus there are imperatives to minimise the amount of water being used for the irrigation of date palms, and to limit the amount of salt leaching from the rootzone of the date palms. These critical issues provide the underpinning reasons for the research described in this thesis. Environment Agency – Abu Dhabi (EAD) has invested in two research projects to determine the minimum amount of irrigation water, as a function of salinity that needs to be applied to date palms to ensure economic returns from date production. These two projects underpin my doctoral research. Using the Compensation Heat Pulse Method (CHPM) of monitoring sapflow has enabled quantification of palm-tree water use, ETc. This was carried out on three cultivars of differing salt tolerances: the salt-tolerant ‘Lulu, the moderately tolerant ‘Khalas’, and the salt-intolerant ‘Shahlah’. Two salinities of groundwater were considered: 5 dS m⁻¹ and 15 dS m⁻¹. The sustainable daily rate of irrigation was considered to be 1.5 ETc, which accounts for a 25% factor-of-safety, and a 25% salt-leaching fraction. This represents considerable savings over current practices. As well, both proximal and remote sensing were used to extrapolate these findings onto commercial date farms. Finally, an assessment of the green, blue and grey water footprints of date production was made. The grey-water footprint from salt leaching was found to be the largest. A benefit-cost assessment was made of the option of using desalinated water to augment and dilute the brackish groundwater used for irrigation. To dilute 15 dS m⁻¹ groundwater to 5 dS m⁻¹ irrigation water was shown to have a benefit-cost ratio of 1.4. However, the environmental impact of the reject brine will need to be considered.Item Soil water use by apple trees : a thesis presented in partial fulfillment of the requirements for the Master of Agricultural Science in Soil Science at Massey University, New Zealand(Massey University, 1989) Rahardjo, PudjoThe study investigated the soil water use of an unirrigated tree and an irrigated apple tree in Hawke's Bay, New Zealand in the middle of the summer of 1988/1989. A rainout shelter was used to eliminate any water inputs from both irrigation and rain to the unirrigated tree. The irrigated tree received water inputs from both irrigation and rain. The soil water content was measured by neutron probing and time domain reflectometry. The heat pulse technique was used to measure the sap-flow in the apple trunks. Both leaf water pressure potential and stomatal resistance were measured by the pressure chamber and porometer respectively. A measuring cylinder was used to monitor the apple growth during the study. The results of the water use measurements were that - the neutron probing and time domain reflectometry showed the soil water use was about 77 litres (4.3 mm) per day taken from 0 - 1900 mm depth around the irrigated tree. However soil water extraction around the unirrigated tree was only 19 litres (1 mm) per day at the beginning of the study, and no water extraction was measured from the top 1900 mm later in the study. - the heat pulse technique showed that the unirrigated tree extracted slightly more soil water than the irrigated tree. The average sap-flow measured was 66 litres per day. Probably the unirrigated tree extracted much of its water from below 1900 mm depth, or from beyond the covered area. - the amount of water use by the apple trees was similar to regional evaporation estimates obtained using the Priestley - Taylor formula, when 0.66 fractional canopy cover was assumed. The water stress monitoring showed that a pressure chamber technique was a more sensitive way to monitor ress than was porometry. e leaf water pressure potential values showed a significant difference between the irrigated and the unirrigated apple tree ring the latter part of the study. The readily available soil water storage capacity from 0 to 400 depth (the most active part of the root zone) , from 0 - 1000 mm h, and from 0 to 1900 mm, was about 36 mm, 89 mm and 170 mm actively. When there was a lack of available soil water on the oil, the root system was forced to extract soil water from deep in soil profile. The comparison of apple fruit growth showed that during the last days of the study, the apples on the unirrigated tree grew more ly than those on the irrigated tree.Item The response and recovery of ten hill country pasture species subjected to water deficit stress : a thesis presented in fulfilment of the requirements of Masters in Agricultural Science(Massey University, 1995) Davis, James Robert AndrewThe objectives of this study were to screen the response of several pasture species when subjected to water deficit stress, use these responses to test some predictions of plant strategy theory (Grime el al. 1988) in relation to stress, and examine some plant functional characteristics related to stress and interpret the responses in relation to plant community structure in hill country pastures. The rationale here is that by testing a range of species responses to controlled stress in artificial conditions significant patterns of ecological specialisation in plant traits may be detected Ten hill country pasture species were exposed to a controlled water deficit stress in a glasshouse experiment. The response of the plants to a progressively severe water stress followed by the resumption of water and nutrient supply for a three-week recovery period was assessed, using measurements of leaf extension, dry mass, senescence and tissue nutrient contents The ranking of species for resistance to water stress (defined as the ability of the plant to continue functioning during the stress) based on the measurements of leaf/petiole extension rate, was (lowest to highest): Lolium perenne < Dactylis glomerata < Holcus laiKitus < Agrostis capillar is < Plan/ago lanceolata < Agrostis caste I tana < Trifohum repens < Rytidosperma clavatum < Lotus cornicaiatus < Hieraaum pilose/Ia l.olium perenne. Dactylis glomerata and Rytidosperma clavatum, followed by Trifolium repens showed the highest resilience (defined as the rate of recovery after the stress is removed) again measured by leatfpetiole extension rate The difference in total dry mass between control and stress treatments was used to assess the effect of the stress on biomass accumulation Those species classified with C attributes according to plant strategy theory survived the water stress through rapid plastic adjustments in leaf extension and senescence and developed a large difference in dry mass between the stress and control treatments The stress tolerant type species had the least response in terms of difference in biomass accumulation and senescence The broad differences between plants with S-type and C-type attributes are consistent with plant strategy theory. However within the CR-CSR classification several different types of response to water deficit stress were evident In particular, the CR-CSR strategists l.olium perenne and Dactylis glomerata showed a well developed capacity to cease leaf elongation early and senescence leaf material so as to preserve meristems in a viable state to allow recovery when water supply resumed Other CR-CSR strategists did not have this capacity and several species died as a result of water stress This suggests that secondary functional types may be recognised within the primary types of CSR theory The results are discussed in relation to the coexistence of hill country pasture species It is suggested that the persistence of l.olium perenne and Dactylis glomerata in hill country pastures may be partly related to a capacity for rapid plastic adjustments in leaf extension and leaf area so preserving dormant vegetative meristems during water stress, allowing rapid recovery in the cooler period of the year with adequate water.Item A study of growth, development and N-fixation of several white clover (Trifolium repens L.) cultivars under different water deficit and phosphorus levels : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand(Massey University, 1991) Wang, XinjunWhite clover (Trifolium repens L.) is one of the most important pasture plants in New Zealand. It contributes nitrogen, high quality forage and seasonal spread of production. However, it has high requirements for phosphate and does not persist well under moisture stress condition.s In this study the effects of water deficit level and phosphorus (P) level on the growth, development and N-fixation of different white clover cultivars have been studied. Several New Zealand and overseas white clover cultivars of contrasting morphological characteristics were selected for this study. These cultivars were Kopu, Pitau, Dusi, Haifa, Huia, Tahora and Whatawhata. The main objectives of this study were to determine the effects of water stress and phosphorus levels on growth, development, and N-fixation of these cultivars and to identify the plant characteristics most effective in distinguishing the cultivars used in the study. The research approach was to measure the responses of these cultivars to water deficit and P fertility treatments; and the responses were then related to selected plant characteristics, particularly morphological characteristics. Attempt was also made to distingish the cultivars using multivariate analysis techniques. The results of this study showed that the cultivars had responded differently to water deficit treatment and P treatment. The retardation they suffered in their growth and development, expressed by both dry weight (DW) and growth rate of stonon components (leaf, petiole and branch), was significantly different and, in many cases, could be related back to their morphology and development characteristics. Cultivars of small stature, such as Whatawhata and Tahora, were generally less affected by the stress treatments. Cultivars grown well under control conditions, such as Kopu and Haifa, suffered more severely under stress conditions. For all cultivars, parameters association with leaf area were more sensitive to water deficit stress than those associated with growing points. The study of plant water status of these cultivars under progressively decreasing water availability failed to identify any significant difference between the cultivars in their ability to avoid dehydration at medium to high water deficity stress levels. So it could be suggested that the diference between the cultivars represented their ability to tolerate water stress and was unlikely to be associated with their dehydration avoidance ability but more likely to be associated with morphological characteristics such as deep root and reducing leaf area when water deficit stress occurred. The cultivats were different in their N-fixation ability, as measured by the acetylene reduction analysis (ARA), and this difference was related strongly to leaf size. But when expressed as ARA per unit DW, the difference between the cultivars was non-significant. Overall, under control conditions, mainly the morphological characteristics, such as leaf size, leaf weight and petiole length, caused the difference between cultivars, other characteristics, such as the plant DW components, DW partitioning, and P and N partitioning in plant components, were less important. Among the morphological characteristics, leaf size and leaf weight per stolon were the most important characteristics differentiating between cultivars. These two characteristcs were also the most important for determining plant yield. Under water deficit stress and P deficiency treatment, root DW and branch number were the two most important characteristics differentiating between the cultivars. ABSTRACT White clover (Trifolium repens L.) is one of the most important pasture plants in New Zealand. It contributes nitrogen, high quality forage and seasonal spread of production. However, it has high requirements for phosphate and does not persist well under moisture stress conditions. In this study the effects of water deficit level and phosphorus (P) level on the growth, development and N-fixation of different white clover cultivars have been studied. Several New Zealand and overseas white clover cultivars of contrasting morphological characteristics were selected for this study. These cultivars were Kopu, Pitau, Dusi, Haifa, Huia, Tahora and Whatawhata. The main objectives of this study were to determine the effects of water stress and phosphorus levels on growth, development, and N-fixation of these cultivars and to identify the plant characteristics most effective in distinguishing the cultivars used in the study. The research approach was to measure the responses of these cultivars to water deficit and P fertility treatments; and the responses were then related to selected plant characteristics, particularly morphological characteristics. Attempt was also made to distinguish the cultivars using multivariate analysis techniques. The results of this study showed that the cultivars had responded differently to water deficit treatment and P treatments. The retardation they suffered in their growth and development, expressed by both dry weight (DW) and growth rate of stolon components (leaf, petiole and branch), was significantly different and, in many cases, could be related back to their morphology and development characteristics. Cultivars of small stature, such as Whatawhata and Tahora, were generally less affected by the stress treatments. Cultivars grown well under control conditions, such as Kopu and Haifa, suffered more severely under stress conditions. For all cultivars, parameters associated with leaf area were more sensitive to water deficit stress than those associated with growing points. The study of plant water status of these cultivars under progressively decreasing water availability failed to identify any significant difference between the cultivars in their ability to avoid dehydration at medium to high water deficit stress levels. So it could be suggested that the difference between the cultivars represented their ability to tolerate water stress and was unlikely to be associated with their dehydration avoidance ability butItem Effects of water stress at different stages of growth on seed yield of safflower : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University(Massey University, 1977) Brookfield, Paul Leighton PurchasSafflower plants were grown from seed in controlled environment rooms. The light and dark period temperatures were 23°C and 18°C respectively. Plant water deficits of -8 to -10 bar were imposed for 20 days during each of the periods floral initiation, inflorescence development, flowering, the post flowering period, and for 12 days during secondary head flowering. Water stress during floral initiation or inflorescence development significantly reduced yield over water stress at any other stage of growth. Seed yield was reduced 46% and 57% by water stress during floral initiation and inflorescence development respectively, compared with well watered plants. Of the sequentially developing traits of seed yield, number of seeds per head accounted for most variation in seed yield, followed by number of heads per plant. Seed weight had relatively little effect on variation in seed yield. Water stress at floral initiation reduced seed yield due to a 32% reduction in head number per plant at final harvest. Fewer florets developed in each head, contributing to a 53% reduction in the potential seed number per plant. Water stress during inflorescence development reduced the number of heads per plant by 30% and the number of seeds per head by 34%. Water stress during the flowering period reduced seed weight by 23%. This was attributed to a 38% reduction in seed hull weight. Water stress after flowering reduced seed hull content by up to 15% and was associated with a higher seed oil content of 26.5% compared with 22.3% for well watered plants. It was concluded that safflower should be planted early to minimise the risk of water stress during inflorescence development, and that seed quality may be improved by dry conditions after flowering. From the results it was suggested that safflower may not necessarily be dependant on an extensive root system for its independence of late season rainfall.Item Drought resistance mechanisms in "Mediterranean" perennial ryegrass (Lolium perenne L.) and potential for introgression of "Mediterranean" germplasm into New Zealand commercial cultivars : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science, Massey University, Institute of Agriculture and Environment, College of Sciences, Palmerston North, New Zealand(Massey University, 2013) Hussain, SajjadThe unique topography of New Zealand creates a wide variation in rainfall and temperature between and within the two islands of the country. As a result, successful use of perennial ryegrass (Lolium perenne L.), the backbone of New Zealand’s agricultural economy, has been restricted to only the higher rainfall and cooler areas of the country. However, there has been only limited analysis of drought resistance in forage grasses at the trait level. This PhD study was conducted on a perennial ryegrass cultivar “Medea” developed in Adelaide in the 1960’s from reportedly drought resistant and summer dormant germplasm of North African origin. The main objectives of the study were to compare Medea with a high yielding but drought susceptible current New Zealand cultivar, Grasslands Samson for their drought resistance potential and to evaluate Medea for its suitability for introgression with Grasslands Samson, in a plant improvement programme. Drought resistance strategies of Tolosa, Matrix and Ceres One50 were also evaluated. In total six glasshouse experiments were conducted. Experiment 1 (April – September 2008) compared winter vegetative growth of potted plants of Grasslands Samson and Medea. Yield of Medea was <50% that of Grasslands Samson, but glasshouse temperature at times exceeded 25°C, so it is possible that this temperature was high enough to partially trigger summer dormancy in Medea. In Experiment 2 (summer 2008 – 2009) techniques for assessing drought resistance were developed, and in Experiment 2 and Experiment 5 (summer 2009 – 2010) drought resistance strategies exhibited by individual cultivars were evaluated. Experiment 2 included Medea, Grasslands Samson, an unreleased tetraploid breeding line developed from Grasslands Samson and Tolosa. Experiment 5 evaluated Matrix and Ceres One50, in addition to Grasslands Samson and Medea. Drought resistance strategies observed in Medea included deep rootedness and high leaf proline contents, but there was some evidence for lack of transpiration reduction in water deficit stress. Medea had prolific flowering. Grasslands Samson and its tetraploid were more productive than Medea in these experiments. However, Tolosa produced the same shoot DW as Grasslands Samson with greater retention of soil moisture, indicating higher water use efficiency. Experiment 3 (March 2009 – February 2010) compared five family groups, each comprising a Grasslands Samson and a Medea parent, and three of their F1 progeny. In this experiment plants were 11 months old when root traits were evaluated and for these older plants, Grasslands Samson had a higher root to shoot ratio and deep rootedness than Medea. Medea plants had similar shoot DW to Grasslands Samson plants during winter, but 46% lower shoot DW in summer. The F1 progeny showed positive mid-parent heterosis for deep rootedness, but negative mid-parent heterosis for shoot DW, and tended to reflect the prolific flowering of the Medea parent. Experiment 4 (December 2009 – June 2010) compared six family groups of F2 progeny for traits related to drought resistance. Although plant numbers were small compared with a commercial breeding programme, it was evident some family groups combined both drought resistance and productivity traits. Experiment 6 (September 2011 – February 2012) evaluated Grasslands Samson, Medea, and F1 and F2 progeny for drought resistance traits. Some useful traits expressed strongly in the F1 generation reverted to mid-parent values in the F2 generation. Some genotypes of Grasslands Samson exhibited higher water use efficiency (reduced soil moisture extraction with high shoot DW) and this warrants further research. It is concluded that some desirable genes for traits contributing to drought resistance, such as deep rootedness and osmotic adjustment might be obtained from Medea. However, the drought resistance strategy of Medea involving reduction in plant size in summer, deep rooting and comparatively high transpiration would have pros and cons for New Zealand farmers as a trait combination. Reduced depletion of soil moisture under water deficit might assist survival of companion plants such as white clover; but high transpiration would decrease water use efficiency. Therefore, improving the water use efficiency of Grasslands Samson or use of material such as Tolosa, which has a comparatively low soil water use per unit of dry matter produced among the cultivars tested, would appear to be a preferred breeding strategy for future breeding programmes in New Zealand.