No description available.

This study aims: 1) To quantify the factors affecting the changes of site water status of the high sand tailings, 2) To investigate the growth and physiological responses of <I>Acacia mangium </I>and <I>A. auriculiformis </I>to the fluctuations of site water status on high sand dunes, and 3) To identify characteristics which may allow the trees to adapt to and survive on high sand tailings. In both shade and open plots on sand tailings, diurnal air water deficits would be anticipated particularly in sunny days and late afternoon in cloudy days. The results from dipwell showed that the main source of soil water supply to the sand tailings is solely dependent on the rainfall and not from surrounding mining pools. Furthermore, at 6 d after rainfall <37 mm, sand tailings at 0-15 cm depth had low sand suction showing soil water deficit to plant uptake. Hence, the rainfall distribution would determine the growth of acacias in sand tailings. Dry periods significantly reduced (P<0.05) the shoot length and stem diameter growth rates and leaf area of both acacias. Dry periods also significantly increased leaf and branch number shedding rates of both acacias. Generally, shading did not improve the growth rates of both acacias in dry periods but significantly delayed leaf shedding of the two acacias in dry periods. <I>A. auriculiformis </I>had significantly higher shoot length and stem diameter growth rates as the result of higher leaf and shoot numbers. The superiority of <I>A. auriculiformis</I> compared to <I>A. mangium </I>in adapting to high sand tailings was explained by its growth patterns that had characteristics of drought avoidance, and/or tolerance. Greater vegetative growth was observed in <I>A. auriculiformis </I>than <I>A. mangium </I>in wet periods. The effects of atmospheric and soil water fluctuations on some physiological responses of the two species were also examined.

In the first year, two upland rice varieties (Azucena and Bala), were screened for root response to drought at the West Africa Rice Development Association (WARDA), Cote d’Ivoire, in two fields of slightly different soil penetration resistance (PR) characteristics.  Changes in soil PR and soil water content were monitored during the drought period.  Root density and depth were significantly greater for Azucena than Bala, and on the irrigated plots compared to the droughted plots, although no consistent site differences in root density were observed.  At each site, on the droughted subplot, soil PR quickly increased near the surface (0-30 cm) in response to reduction in soil water content and soil matrix potential caused by root water extraction.  It is likely that this increase in PR would have either prevented or reduced the rate of downward growth of new roots entering or growing within this layer.  Under these conditions, varietal differences in root response to impedance would be important for drought avoidance. In the second year, also at WARDA, a mapping population based on a cross between Azucena and Bala were tested in two fields of contrasting soil physical properties and QTL for root density at 35 cm were identified.  There was no agreement between sites.  Site characterisation prior to field screening revealed the two sites to be very different in terms of soil texture and water relations.  These site differences would have restricted root growth in different ways and are likely to be reasons behind the lack of agreement in root density QTL between sites. In the third year, near-isogenic lines (NILs) differing only in single or multiple root growth QTL were screened in fields at the International Rice Research Institute (IRRI), Philippines, in soils of lower mechanical impedance than sites used at WARDA.  No major differences were observed for root density indicating the importance of interaction between root traits and the environment when considering contribution to drought resistance.

A combination of root morphology and plant physiology with drought/or salt tolerance should affect drought resistance in cotton (Gossypium hirsutum L.). This experiment was developed to evaluate early vegetative and seedling growth of cotton from the unselected parents with two selected populations of M-8844-0100, DPL 50, and TAM 94L-25 across two cycles for seedling drought. Three genotypes from three generations of selection were grown in tubes to evaluate early growth and in containers to evaluate seedlings for drought resistance in a greenhouse at College Station, TX in 2008 and 2009. The experiment during the winter months of 2008 resulted in shorter tap root length, fewer lateral roots, and lower fresh and dry weight for total root, lateral roots, and shoots. The drought selections in these genotypes affected the tap root fresh weight, and the number and weight of lateral roots. TAM 94L-25 averaged higher tap root fresh and dry weight, lateral root fresh weight and shoot fresh weight. DPL 50 exhibited greater weight of lateral roots and shoot fresh weight. No difference was found in percent wilting across generations for drought at 75 percent apparent wilting and recovery at 90 percent apparent wilting.

No description available.

Effects of mineral nutrition on drought and cavitation resistance of poplars were examined in two sets of greenhouse-grown trees. First, two drought-sensitive and two drought-resistant hybrid clones of black cottonwood (Populus trichocarpa Torr. & Gray) and eastern cottonwood (P. deltoides Bartr.) were grown at three concentrations of nitrogen (N) applied factorially with two concentrations of phosphorus (P) in a sub-irrigation sand-culture system. The trees were subjected to 0, 4, 6, and 8 days of gradual drought stress before measurements of cavitation, anatomical features affecting cavitation, and nutrient mobilization during drought. High foliar concentrations of N increased cavitation compared to barely adequate concentrations, whereas high concentrations o f P decreased cavitation as measured by both hydraulic flow apparatus and dye perfusion techniques. For one test, cavitation was 48% at high N and low P, but only 28% at high N and high P. Vessel pit membrane mean pore diameters were 0.132 μm at low P and 0.074 μm at high P: smaller pores would decrease air-seeding cavitation. No other significant effects of mineral nutrition on vessel dimensions were observed. Scanning election microscopy showed less damage to pit membranes, suggesting greater membrane strength in drought-resistant clones than in drought-sensitive clones. In the second experiment, three drought-resistant and three drought-sensitive poplar clones (including P. trichocarpa) were grown at two levels of N and three levels of potassium (K) and either well-watered, cyclically droughted, or droughted once. Cavitation, osmotic potential, gas exchange, and nutrient mobilization were measured at each stage of drought and re watering, and fall nutrient retranslocation was monitored. Cavitation was greater with adequate foliar N than at deficiency levels. Moderate supplies of K increased cavitation, but luxury levels sometimes reduced cavitation by decreasing foliar water loss and thus xylem tension. Preconditioning did not reduce vulnerability to cavitation, but there was some evidence of cavitation reversal in a drought resistant clone at high N supply. Vessel diameters were 36.6 μm at low N but 45.2 μm at high N, so within Populus, larger diameter vessels correlated with susceptibility to cavitation. High N supply increased water stress during the first drought, but also increased instantaneous water use efficiency (WUE) before drought occurred, and osmotic adjustment and hardening after drought. Increased K also increased WUE before drought and decreased water stress (decreasing transpiration and wilting) at luxury levels, but did not influence osmotic adjustment or hardening. Mobilization of nutrients differed with speed and intensity of drought. Gradual drought led to resorption of N and P. In the second experiment, drought was too rapid for retranslocation. Nutrients became more concentrated; some (e.g., N) facilitated hardening and osmotic adjustment, and some (e.g., K) moved out of the leaves on re watering. In fall, N, P, Cu and K were resorbed, the latter more proficiently with greater N supply at low levels of K. Clones which were more productive on dry sites resisted severe, but not moderate cavitation. Cavitation-resistant clones maintained high transpiration rates (and less negative water potentials) in drought, especially after hardening, had more, but smaller, stomata and decreased leaf loss in drought, but did not have increased WUE or osmotic adjustment. Nitrogen fertilization increased cavitation, greater P supply reduced this effect, and K fertilization may make vessels more vulnerable to cavitation but decrease the tension on the xylem that causes cavitation. Nitrogen fertilization levels should be tailored to site water supplies, and appropriate P, and possibly K additions may increase drought resistance. / Graduate

Bibliography: leaves 187-216.

This dissertation is comprised of three essays that generate methods to measure the ex-ante economic impacts of agriculture technology innovations. The first essay entitled 'Valuing Intellectual Property Rights in an Imperfectly Competitive Market: A Biopharming Application' presents a method for valuing the intellectual property rights (IPRs) for an innovation that lowers product production costs below those associated with the patented process of a monopolist. The application to Glucocerebrosidase enzyme from transgenic tobacco suggests an intellectual property rights (IPRs) value of about $1.75 billion. Despite the innovator's market power, significant surplus gains also accrue to consumers. Further, U.S. antitrust laws that prohibit IPRs acquisition by the current monopolist increase consumer welfare by almost 50 percent. The second essay entitled 'Ex-Ante Analysis of the Benefits of Transgenic Drought Tolerance Research on Cereal Crops in Low-Income Countries' develops a framework to examine the ex-ante benefits of transgenic research on drought in eight low-income countries, including the benefits to producers and consumers from farm income stabilization and the potential magnitude of private sector profits from IPRs. The framework employs country-specific agroecological-drought risk zones and considers both yield increases and yield variance reductions when estimating producer and consumer benefits from research. Benefits from yield variance reductions are shown to be an important component of aggregate drought research benefits, representing 40 percent of total benefits across the eight countries. Further, estimated annual private sector benefits of $US 178 million suggest that significant incentives exist for private sector participation in transgenic drought tolerance research. The third essay entitled 'Ex-Ante Evaluation of Alternative Strategies to Increase the Stability of Cropping Systems in Eastern and Central Africa' examines the ex-ante economic impact of transgenic drought resistance maize breeding and of conventional maize, millet and sorghum drought resistance breeding in Kenya, Uganda, and the Amhara region in Ethiopia. An expected utility framework is combined with a partial equilibrium model and a spatial drought risk zonation scheme to estimate benefits from mean yield increases and yield variance reductions at the market level as well as at the household level for maize, millet and sorghum producers in the administrative regions of each country. Results suggest that annual ex-ante benefits of $87 million, $6.8 million and $4.8 million can be generated from public sector conventional breeding research on maize, sorghum and millet, respectively. Private sector transgenic drought tolerance research may also generate substantial benefits of $97 million for maize producers and consumers, particularly through the reduction of yield variance arising from drought, and an additional $21 million as profits from intellectual property rights protection. / Ph. D.

A four-year drought, increasing population and shifting climate has spurred water conservation practices within Virginia. Creeping bentgrass (<i>Agrostis palustris</i> "L93"), Kentucky bluegrass (<i>Poa pratensis </i>"Midnight"), and tall fescue (<i>Festuca arundinacea</i>) Dominion blend were evaluated under deficit irrigation and upon exogenous application of plant growth stimulants (PGS), seaweed extract (SWE) + humic acid (HA), glycinebetaine (GB) and a commercial SWE product (PP). The objectives were to determine crop coefficients (K_c) for creeping bentgrass fairways and tall fescue home lawns, to determine if PGS application allowed for more water conservation, and to determine if they impacted physiological function and/or root morphology. A preliminary greenhouse experiment was conducted with creeping bentgrass and Kentucky bluegrass irrigated with 100%, 85% and 70% of evapotranspiration (ET). The study determined that an additional deficit irrigation level should be included for the field study and that GB application and 100% and 85% ET irrigation level produced the greatest creeping bentgrass root mass. The two–year field study evaluated creeping bentgrass and tall fescue. Tall fescue home lawns could be irrigated every five days with a K_c of 0.55 or once a week with a K_c of 0.70. Creeping bentgrass fairways could be irrigated every four days with a K_c of 0.85. Glycinebetaine application increased bentgrass rooting after planting and showed osmoprotectant properties. Another greenhouse study evaluated five GB rates on bentgrass and tall fescue. No differences were found between the five rates and concluded that the rate utilized in the field study may be appropriate for turfgrass application. / Master of Science

Bibliography: leaves 187-216 / xxi, 216 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Physiology, 1987