Germination of plants is one of the most important stages during their growth which is often influenced by environmental stresses, especially drought and salinity. This study was conducted to investigate the effects of salinity and drought on seed germination and growth of Lathyrus sativa. The experiment was laid out in a completely randomized design with factorial arrangement in 4 replications. Salinity treatments were 0, 2, and 4 dS/m and drought treatments included 0, 0.4, 0.8, 1.2 MPa. Salinity and drought treatments were prepared by using sodium chloride and polyethylene glycol 6000, respectively. The results showed that salinity and drought stresses decreased germination percentage, root and radicle length.

The chromosome substitution (CS) lines constitute an important genetic and breeding resources, increasing the genetic diversity of Upland cotton from other alien tetraploid species. Two experiments were conducted to quantify low temperature and drought stress effects during early growth stages in 21 cotton CS-lines with parent, Texas Marker (TM)-1. In Experiment I, plants were grown at optimum (30/22°C) and low (22/14°C) temperatures under optimum water and nutrient conditions. In Experiment II, plants were grown at optimum water and drought conditions. Above- and below-ground growth parameters including several root traits were assessed at 25 days after seeding. CS-lines varied significantly varied for many traits measured. Combined low temperature and drought response indices, derived from all measured parameters, showed CS-T04 and CSB08sh showed significantly higher and lower tolerance to low temperature, respectively, while CS-T04 and CS-B22sh showed significantly higher and lower tolerance to drought condition compared to TM-1.

Heat shock proteins (HSPs) are expressed in response to environmental stresses. Compared to other kingdoms, plant HSP families are larger, presumably the result of adaptation to a wide range of stresses. Following on an analysis of drought stress characteristics in loblolly pine (Watkinson et al., 2003), expression patterns of HSP gene expression during photosynthetic acclimation were examined. One cycle of mild (-1Mpa) followed by two cycles of severe stress (-1.7Mpa) were probed for conditioning effects. Photosynthetic acclimation occurred after the first cycle. No acclimation occurred without the first mild cycle. Microarray/RT-PCR analyses showed that a pine homolog to GRP94 (ER-resident HSP90) was up-regulated after rehydration coincident with acclimation. This GRP94 is closely related to GRP94 from the desiccation tolerant plant X. viscosa, supporting the importance of this gene during acclimation to water deficit. HSP genes whose products localized to the mitochondrion showed gradual up-regulation after consecutive cycles of severe drought. The Arabidopsis pine GRP94 homolog, (AtHSP90-7) was then analyzed, using bioinformatics (Pati et al., 2006) and laboratory tools. Genes encoding putative candidate co-chaperones for GRP94 and other HSP90s were discovered, which contained water stress-related cis-elements. Arabidopsis (Col-0) wild type and two T-DNA insertion mutants in HSP90-7 were used to study the importance of this gene for photosynthetic acclimation. Only the mutants were able to acclimate to drought stress, with the level of AtHSP90-7 expression in the mutants being reduced compared to the wild type. AtHSP90-7 may have a different role in Arabidopsis, and its reduced expression activated other protective genes (Klein et al., 2006). Responses to extreme drought in resistant (Sullu) and susceptible (Negra Ojosa) lines of Andean potatoes were also compared in order to identify relationships between HSPs gene expression, and tolerance, defined as the ability to maintain photosynthesis at 50% after 25 days of drought and to recover from the stress. Tolerance was correlated with up-regulation of HSPs (mostly chaperonins) and antioxidant genes all of whose gene products are located in the chloroplast. / Ph. D.

Urban soils are typically degraded due to land disturbance. The poor quality physical and chemical properties of the soil can benefit from application of organic amendments. Local sources of such amendments are biosolids, which are treated domestic wastewater sludges. The objective of this experiment was to compare effects of various high quality biosolids-based soil amendments with synthetic fertilizer on the growth and quality of tall fescue (Schedonorus arundinaceus) under two different soil moisture regimes. The research site was a disturbed soil at the Virginia Tech Turfgrass Research Center in Blacksburg, Virginia. The experimental design was a split plot with irrigation regime as the main factor and soil amendments as the split factor. All treatments were arranged in four randomized complete blocks. The study was established in late summer 2013. Soil amendment treatments, applied prior to seeding in September 2013, were: 1) inorganic N, P, K applied according to soil test laboratory recommendations; 2) anaerobically digested, dewatered biosolids to supply agronomic N rate; 3) anaerobically digested, dewatered biosolids blended with sand and sawdust to supply agronomic N rate; 4) anaerobically digested, dewatered biosolids blended with sand and sawdust to supply agronomic P rate; and 5) composted biosolids to supply agronomic N rate. The agronomic N rate for the turfgrass was 224 kg of estimated plant available nitrogen (PAN) ha-1. Inorganic fertilizer was applied to supply annual P and K requirements prior to seeding in late summer, and the N was split into three application timings (September 2013, April 2014, and June 2014). Supplemental fertilizer N to achieve full agronomic N rate was applied to the treatment plots that received the agronomic P rate of blended biosolids-sand-sawdust. The area was seeded on September 13, 2013 with a tall fescue blend at a rate of 488 kg ha-1. Following full tall fescue establishment, in June 2014, two irrigation regimes, consisting of 0% and 80% evapotranspiration replacement every three days, were initiated. The study had three phases denoted as the pre-drought, drought, and recovery phases which started in April and concluded in August of 2014. Turfgrass color and quality, volumetric soil moisture percentage to a 5 cm depth, normalized difference vegetative index (NDVI), clipping yield, and turfgrass N uptake were measured bi-weekly throughout the growing season. During the first May through July 2014 irrigation season, results were that the fertilizer control consistently provided improved responses relative to the biosolids amended treatments. Clipping yield, quality, and NDVI were all significantly greater in the inorganic fertilizer treatment, but volumetric soil moisture percentages were slightly greater in the biosolids treatments. Turfgrass responses appeared to have been associated with plant available nitrogen, which was lower in the biosolids treatments than in the fertilizer treatment. Calculated PAN for the biosolids products was too low to achieve ideal turfgrass growth and quality. Improving the estimated PAN and/or splitting the organic amendment application times should improve the growth and quality of the turfgrass. / Master of Science

No description available.

Herbivory by Western Flower Thrips (Frankliniella occidentalis Pergande) (WFT) and drought-stress due to limited water availability are currently two major factors that can severely impact cotton (Gossypium hirsutum L.) production. This dissertation examines the effects of drought-stress on cotton and host-plant resistance (HPR) to WFT in laboratory conditions, and seeks to identify the physiological and morphological mechanisms that underlie drought-tolerance and HPR. A life-history systems-approach was developed that provides a new level of detail for understanding how environmental variation impacts adult female WFT. The approach was illustrated by investigating the combined effects of cotton genotype, periodic drought-stress, and prey availability on the adult female omnivorous thrips using a factorial design. Three treatment conditions were significantly different, none of which were predicted based on prevailing ecological-hypotheses. At the same time, the approach produced three novel insights about WFT life-history and reproductive strategy. The roles of negative photo-taxis and leaf biomechanical properties were investigated as potential mechanisms that influence WFT foraging-decisions on individual cotyledons. Results showed that WFT foraging-decisions could be considered adaptive, but there was limited support for either of the mechanisms investigated. The physiological responses to drought stress and drought recovery were investigated for three transgenic cotton cultivars and an untransformed wild-type (WT). At peak drought, ABA levels, stomatal area, and stomatal apertures in the transgenic isolone, AtRAV1-1 were 48% lower, 27.7%, and 16.3% smaller than WT. These results suggest that AtRAV1-1 was the most drought-tolerant and support the hypothesis that changes in stomatal morphology may have functionally contributed to drought-tolerance. Lastly, I investigated whether changes in phytohormone concentrations associated with periodic-drought stress in four cotton cultivars (three transgenic and WT) were correlated with WFT feeding, fitness and state-dependent reproductive responses (i.e., the relationship between initial weight and reproduction). Results showed that JA-Ile and JA were positively correlated with state-dependent egg viability and fecundity, respectively, and negatively correlated with total egg viability and fecundity, respectively, supporting the hypothesis that JA and JA-Ile underlie the negative effects on WFT reproduction and the associated shift to state-dependent reproduction.

Le tocophérol, le phytostérol, le pourcentage de protéines des graines, l'huile et les teneurs en acides gras ont été mesurés dans une population de lignées recombinantes (RILS) de tournesol, cultivées sous conditions de sécheresse, irrigation et semis tardif. Une analyse génétique de QTL a été réalisée à partir de ces mesures, en utilisant une carte génétique basée sur des marques SSR et avec des gènes candidats (1) impliqués dans la voie métabolique de tocophérol et phytostérol, (2) des gènes codant des antioxydants enzymatiques, (3) des gènes liés à la sécheresse et (4) des gènes homologues à SEC14 chez Arabidopsis. Trois gènes candidats importants (VTE4, VTE2 et HPPD), qui codent pour des enzymes impliquées dans la biosynthèse du tocophérol, ont été cartographiés sur les groupes de liaison LG8 et LG14. Quatre SNPs sont identifiés pour PAT2, le gène homologue chez Arabidopsis SEC14, entre les deux parents (PAC2 et RHA266) et un SNP, identifié par alignement de séquences est converti en marqueur CAPS pour permettre l'analyse génotypique des RIL. Les gènes homologues à SFH3, HPPD, CAT et CYP51G1 ont été cartographiés grâce à la mise au point de marqueurs dominants, tandis que des marqueurs co-dominants ont permis la cartographie des gènes homologues à SEC14-1, VTE4, DROU1, POD, SEC14-2 et AQUA. Les gènes POD, CAT et GST, codant pour des antioxydants enzymatiques, ont également été cartographiés sur les groupes de liaison 17, 8 et 1, respectivement. Le QTL majeur pour la teneur en tocophérol a été identifié sur le groupe de liaison 8, qui explique 59,5% de la variation phénotypique (6.TTC.8). Il colocalsie également avec le QTL identifié pour la teneur en phytostérol (7.TPC.8). Sous condition de semis tardif, un QTL spécifique de la teneur en acide palmitique a été identifié sur le groupe de liaison 6 (PAC-LS.6). Il est situé entre les marqueurs ORS1233 et SSL66_1. Les QTLs pour le pourcentage d'huile de graines et la teneur en acide stéarique colocalisent sur les groupes de liaison 10 (PSO-PI.10 et SAC-WI.10) et 15 (PSO-PI.15 et SAC-LS.15). Sept QTLs associés à teneur en acides palmitique, stéarique, oléique et linoléique sont identifiés sur le groupe de liaison 14. Ils sont liés à l’homologue du gène HPPD. Par ailleurs, les caractères agronomiques tels que les jours du semis à la floraison, la hauteur des plantes, le rendement et la morphologie foliaire ont été étudiés. Des analyses association génétique ont permis d’identifier des QTLs intérêts sur les groupes de liaison 2, 10 et 13 pour les caractères étudiés, d’autres QTLs identifies sur les groupes de liaison 9 et 12 mettent en avant l'importance de ces régions génomiques pour les caractères de morphologie foliaire. Nous avons finalement identifié des marqueurs AFLP et quelques gènes candidats liés aux caractères impliqués dans la qualité des graines sous conditions irriguée et stress hydrique chez une population de mutants (M8). Deux lignées mutantes, M8-826-2-1 et M8-39-2-1, produisent un niveau significativement élevé d'acide oléique peuvent être utilisées dans les programmes de sélection en raison de la haute stabilité à l'oxydation et des propriétés cardiovasculaire apportés par l’acide oléique qu’elles produisent. L'augmentation du niveau de tocophérol dans les lignées mutantes, M8-862-1N1 et M8-641-2-1, est justifiée par le polymorphisme observé pour le gène, MCT, impliqué dans la voie métabolique du tocophérol. Le marqueur le plus important pour le contenu en tocophérol total est E33M50_16 qui explique 33,9% de la variation phénotypique. Un des gènes candidats les plus importants concernant la biosynthèse des acides gras, FAD2 (FAD2-1), est lié à la teneur en acides oléique et linoléique. Il explique plus de 52% de la variation phénotypique. / The genetic control of tocopherol, phytosterol, percentage of seed protein, oil and fatty acids content in a population of recombinant inbred lines (RILs) of sunflower under various conditions are studied through QTL analysis using genetic-linkage map based on SSR markers and introducing some important tocopherol and phytosterol pathway-related genes, enzymatic antioxidant-related genes, droughtresponsive family genes and Arabidopsis SEC14 homologue genes. Three important candidate genes (HPPD, VTE2 and VTE4), which encode enzymes involved in tocopherol biosynthesis, are mapped to linkage group 8(LG8) and LG14. One of the most important candidate genes coding for sterol methyltransferase II (SMT2) enzyme is anchored to LG17 by CAPS marker. Four SNPs are identified for PAT2, Arabidopsis Sec14 homologue gene, between two parents (PAC2 and RHA266). PAT2 is assigned to LG2 by CAPS marker. Squalene epoxidase (SQE1) is also assigned to LG15 by InDel marker. Through other candidate genes, POD, CAT and GST encoding enzymatic antioxidants are assigned to LG17, LG8 and LG1, respectively. The major QTL for total tocopherol content on linkage group 8 accounted for 59.5% of the phenotypic variation (6.TTC.8), which is overlapped with the QTL of total phytosterol content (7.TPC.8). Under late-sowing condition, a specific QTL of palmitic acid content on linkage group 6 (PAC-LS.6) is located between ORS1233 and SSL66_1 markers. Common chromosomic regions are observed for percentage of seed oil and stearic acid content on linkage group 10 (PSO-PI.10 and SACWI. 10) and 15 (PSO-PI.15 and SAC-LS.15). Overlapping occurs for QTLs of oleic and linoleic acids content on linkage groups 10, 11 and 16. Seven QTLs associated with palmitic, stearic, oleic and linoleic acids content are identified on linkage group 14. These common QTLs are linked to HPPD homologue, HuCL04260C001. QTLs controlling various traits such as days from sowing to flowering, plant height, yield and leaf-related traits are also identified under well-, partial-irrigated and late-sowing conditions in a population of recombinant inbred lines (RILs). The results do emphasis the importance of the role of linkage group 2, 10 and 13 for studied traits. Genomic regions on the linkage group 9 and 12 are important for QTLs of leaf-related traits in sunflower. We finally identified AFLP markers and some candidate genes linked to seed-quality traits under well-irrigated and water-stressed conditions in gammainduced mutants of sunflower. Two mutant lines, M8-826-2-1 and M8-39-2-1, with significant increased level of oleic acid can be used in breeding programs because of their high oxidative stability and hearthealthy properties. The significant increased level of tocopherol in mutant lines, M8-862-1N1 and M8- 641-2-1, is justified by observed polymorphism for tocopherol pathway-related gene; MCT. The most important marker for total tocopherol content is E33M50_16 which explains 33.9% of phenotypic variance. One of the most important candidate genes involving fatty acid biosynthesis, FAD2 (FAD2-1), is linked to oleic and linoleic acids content and explained more than 52% of phenotypic variance.

Doctor of Philosophy / Department of Agronomy / P. V. Vara Prasad / Sweet sorghum (Sorghum bicolor L. Moench) is an important bioenergy crop. There is a wide array of genetic diversity in sweet sorghum germplasm collections. However, information on traits associated with sugar yield, optimum harvesting time for maximum sugar yield, effects of abiotic stresses on sugar yield is scarce. The objectives of the present study were: to identify traits that are associated with sugar yield, to determine the optimum harvesting time for maximum sugar yield and to understand the physiological responses of different sweet sorghum genotypes to drought and high temperature. In order to meet these objectives, five independent field and greenhouse studies were conducted. Field experiments were conducted using 280 sweet sorghum germplasm and were evaluated for 2 years. From this study, 30 genotypes representing high and low sugar yielders were selected for the subsequent experiment. We observed a significant variation in physiological, morphological and sugar yield traits associated with biofuel production. In the selection experiment, investigations on the morphological, physiological attributes helped to identify those characters which influence or limit sugar yield in the sweet sorghum. Another field study was conducted to optimize the harvesting time for obtaining highest sugar and juice yields in sweet sorghum. Sweet sorghum variety M81E was harvested at ten growth stages. Our results suggest that the optimum time for harvesting of sweet sorghum cultivar M81E is between milk and hard dough stages when highest sugar yield was observed. Studies on different levels of water stress were studied under greenhouse conditions. Four sweet sorghum genotypes (Awanlek, Smith, Tracy and Wray) were subjected to three water stress treatments (100% pot capacity (PC); 70% PC and 30% PC) for 20 days at early seed filling (Milk) stage. The results showed that genotypes differed significantly for all growth and yield, biochemical and physiological traits. Severe water stress significantly decreased juice and sugar yields by decreasing net photosynthetic rate, transpiration rate, stomatal conductance and sucrose content in the stem juice. Genotypes Tracy and Wray produced significantly highest brix, stem fresh weight, juice and sugar yield under both irrigated and water stress conditions. In another greenhouse study, we quantified the effects of drought, high temperature, and their combinations on growth, physiology and yield of sweet sorghum genotypes. The same four genotypes above were subjected to four treatments, T1 - control, T2 - drought stress, T3 - high temperature stress and T4 - combination of drought and high temperature for 16 days after anthesis. The result showed that significant difference was observed for growth and yield traits, physiological traits and non-reducing and total sugar content in juice for genotypes and treatments. Among the genotypes Tracy recorded higher juice and sugar yield. Among the various treatments, combination of drought and high temperature was found to be more deleterious in reducing most of the biofuel traits followed by drought and high temperature stress. The above studies gave significant findings with regards to the identification of superior sweet sorghum germplasm, their tolerance capacity to different abiotic stresses, which allows better selection for the use of bioenergy production.

Doctor of Philosophy / Department of Horticulture, Forestry, and Recreation Resources / Dale Bremer / Greg Davis / In 2005, turfgrass was estimated to cover approximately 20 million ha of urbanized land. That area is increasing with rapid urbanization, stressing the importance of water conservation in the lawn and landscape industry. Turfgrasses have been identified for replacement by presumably more water-efficient ornamental plant species to conserve water. However, research comparing drought resistance and evapotranspiration (ET) of turfgrasses with ornamental landscape plants is limited. Two studies were conducted to evaluate water use and performance under drought stress of several ornamental and turfgrass species. An online course was developed to educate students about critical water issues related to irrigation in urbanizing watersheds. In a field study, ET was measured using lysimeters and plant water status was evaluated under deficit irrigation (100%, 60%, and 20% ET) in Festuca arundinacea Schreb., Buchloe dactyloides (Nutt.) Engelm. ‘Sharps Improved’, and Ajuga reptans L. ‘Bronze Beauty’. Evapotranspiration was similar between A. reptans and F. arundinacea, and was 32 and 35% greater than ET of B. dactyloides. In a greenhouse study, the performance of one turfgrass (Poa pratensis L. ‘Apollo’) and eight landscape species (Achillea millifolium L., Ajuga reptans L. ‘Bronze Beauty’, Liriope muscari Decne., Pachysandra terminalis Siebold and Zucc., Sedum album L., Thymus serpyllum L., Vinca major L., and Vinca minor L.) was evaluated during a severe dry down and subsequent recovery. S. album, L. muscari, and P. terminalis performed the best, requiring 86 to 254 d to decline to a quality rating of one (1-9 scale: 1=dead/dormant, 9=best quality). The remaining species required 52 to 63 d. The only species to recover were P. pratensis [46% pot cover (PC) after 60 days], S. album (38% PC), and V. major (35% PC). A survey was developed to measure student learning as it relates to the level of sense and meaning present in the content of a new online course entitled “Water Issues in the Lawn and Landscape.” Survey results were compared with student learning as measured through a post-test. Post-test scores declined as the difference between sense and meaning increased (r =-0.82; P=0.03), indicating student learning is higher when both sense and meaning are present.

Entre os vegetais existem duas estratégias distintas para superar as condições de estresse hídrico que condicionam a sensibilidade a dessecação (SD) que está associada a mecanismos de evitação e a tolerância a dessecação (TD) que envolve suportar o estresse hídrico diretamente no nível dos tecidos e no nível subcelular. Sabe-se que os custos acoplados aos mecanismos de dessecação e reidratação em espécies TD são elevados, e provavelmente superiores aos de espécies SD. Desta forma, a coexistência de espécies com estas estratégias, como ocorre no ambiente epifítico da Cidade Universitária Armando Sales de Oliveira (CUASO), induzem questões quanto a as vantagens relativas de espécies TD sobre SD. Devido aos altos custos da estratégia TD é possível propor que estas deveriam apresentar um ganho médio de carbono superior a de espécies SD durante o período favorável (com disponibilidade hídrica). Além disso, também é razoável esperar que as distintas formas de uso da água, vinculadas às estratégias, poderiam facilitar o convívio de espécies TD e SD através da segregação de nichos. Com intuito de verificar essas hipóteses, foram realizadas análises relacionadas a estrutura de comunidade de epífitas da CUASO e, a partir destas, a detecção da associação espacial mais freqüente, que resultou composta por Pleopeltis hirsutissima (TD) e Microgramma squamulosa (SD). Estas espécies foram então selecionadas para avaliar parâmetros associados à dinâmica do uso da água, assimilação líquida de carbono, dinâmica da capacidade de uso da luz, estado de hidratação foliar e pigmentos fotossintéticos. Os resultados apontaram que espécies de ambas as estratégias não apresentam sinais de estresse crônico no ambiente estudado. Os dados reforçaram as respostas contrastantes de TD e SD, refletindo as formas distintas de lidar com os recursos e condições do ambiente. Ao contrário do esperado, P. hirsutissima não apresentou uma assimilação de carbono superior a M. squamulosa, indicando que o ganho de carbono não é um dos fatores possíveis na compensação dos custos acoplados a sua estratégia (TD). Porém, os resultados apresentados quanto a dinâmica da capacidade de uso da luz sugerem que a coexistência é facilitada pela segregação de nichos de luz, sendo a espécie TD mais heliófila do que a espécie SD / In land plants the resistance to drought can be accomplished by two main strategies. One involves mainly dehydration avoidance mechanisms and the other is based on the ability to withstand drought at the tissues and down to subcellular levels. The former is found on the desiccation sensitive plants (DS) and the last describes the desiccation tolerant plants (DT). The metabolic costs of the desiccation tolerance mechanisms are probably high, at least when considering the cessation of photosynthesis during anabiosis - a condition that is absent in drought avoidance strategies. The coexistence of drought avoiders and desiccation tolerant plants in the same substrate and condition can rise some questions about the relative advantages of each strategy when submitted to similar water regime. We ask whether desiccation tolerant plants have a compensatory carbon gain under a watering regime that induces frequent anabiosis or cumulative damage in drought avoidance have a detrimental effect comparable to the costs of the desiccation tolerance. An analysis of the epiphytic plant community associated to the trees of the CUASO urban landscape showed a very frequent co-occurring species pair including the desiccation sensitive Microgramma squamulosa and a desiccation tolerant Pleopeltis hirsutissima, both cryptogams of the same plant family. These species were thoroughly examined regarding the patterns of light, water and carbon dynamics together with pigments concentration during cycles of natural drought and wet climate field conditions. These observations were complemented with experimental induction of different water and light regimes. The results showed no sign of chronic stress in both plants living at the same condition but allowed us to identify large distinctions in resource use patterns. A compensatory carbon assimilation was not found in P.hirsutissima. Both species have similar CO2 assimilation values. Experimental induction of drought in different light regimes allowed to verify a relative advantage in desiccation tolerant P.hirsutissima in comparison to the desiccation sensitive M.squamulosa under high irradiance values. Furthermore, light curve analysis suggest that they share the same tree but their niches differ in light intensity regime allowing the high frequency of co-occurrence observed in the field