Potato crops are generally sensitive to drought. Even a short period of water shortage can affect tuber production and quality. However, field potato crops undergoing mild water deficit conditions may acclimate to subsequent severe water deficits. While responses may be both acclimation and genotype-dependent, few studies have examined whole plant physiological factors leading to enhanced drought stress resistance. Identification of these key factors may increase selection efficiency in breeding programs. This study examined the effects of drought acclimation on drought stress resistance in three potato genotypes [‘Fv12246-6’ (Fv), ‘Vigor’ (V) and ‘Russet Burbank’ (RB)] in a low relative humidity greenhouse. Non-Acclimated and Non-Stressed (NA), Drought Acclimated and Drought Stressed (DAS) and Non-Acclimated and Drought Stressed (NAS) treatments were applied. Tuber yield and number were genetically determined and acclimation had no effect on increasing these components under drought stress. However, water conservation mechanisms based on leaf and stem characteristics were both genotype and treatment-dependent. When leaves were drought stressed while attached to the stem, genotype V and RB maintained a higher percentage of leaf water content (%LWC) than Fv, likely from the greater water stored in their stems that may have been delivered through continued leaf transpiration. Acclimation induced a thicker leaf cuticular layer and partially open stomata under drought stress in both RB and Fv. Nevertheless, Fv was the most drought sensitive potato genotype, displaying the highest degree of leaf wilting and lowest %LWC under drought stress. The observed drought stress-induced smaller stomatal size in Fv did not confer greater resistance. In addition, Fv displayed the lowest percentage shoot water content (%SWC) and slowest recovery time after drought stress. RB underwent the fastest recovery from drought stress, possibly due to its equivalent xylem to pith ratio which might have enhanced greater water uptake in RB than in V and Fv. Finally, compared to application of drought stress directly (NAS), a pre-treatment of drought acclimation cycles followed by drought stress (DAS) reduced leaf wilting, induced thicker cuticular layer and more open stomata under stress. Without a DAS approach, potentially key drought stress resistance mechanisms will be missed. The role of the stem as a potential water reservoir to adapt against drought stress should be examined to further identify key elements for drought stress survival and recovery at the level of the potato whole plant.

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.

No description available.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1991. / Includes bibliographical references (leaves 112-124) / Microfiche. / xiv, 124 leaves, bound ill. 29 cm

Thesis (M.S.)--Ohio University, June, 1990. / Title from PDF t.p.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 89-93). Also available via the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 104-107). Also available on the Internet.

Thesis (Ph.D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 104-107). Also available on the Internet.

Thesis (Ph.D.)--University of Delaware, 2005. / Principal faculty adviser: David R. Legates, Dept. of Geography. Includes bibliographical references.