We wanted to develop rapid and cost-effective drought tolerance screening methods for mass amounts of germplasm. In 2009 and 2010, we evaluated sixty-two maize inbred lines and their hybrid testcross progeny using seedling stress response and epicuticular wax accumulation as predictors of drought tolerance. The seedling screening method measured germination, survival and recovery percentages after a series of drought cycles in a greenhouse environment. Eight inbred lines had significantly (P < 0.05) lower germination than the mean estimate, but hybrid testcrosses were not significantly different. The second-to-last day of survival cycle and the second day of recovery cycle best explained genotypic differences for inbred lines and hybrid testcrosses respectively. One inbred line performed well as both an inbred line and hybrid testcross, but poor correlation over the sample set (R2 = 0.0097) was observed. Flag leaves taken at flowering from plants under full and limited irrigation regimes were sampled for epicuticular wax. Extracted wax weight for genotypes was compared as a percentage of leaf weight (percent wxlfwt) and leaf area (percent wxwta). Eleven genotypes had above average percent wxlfwt as both inbred lines and hybrid testcrosses. Thirteen genotypes had above average percent wxwta as either inbred lines or hybrid testcrosses. Irrigation treatment was not significant (P > 0.05). Heritability of percent wxlfwt was 0.17 (inbred lines) and 0.58 (hybrid testcrosses). Heritability of percent wxwta was 0.41 (inbred lines) and 0.59 (hybrid testcrosses). Correlations (R2) for percent wxlfwt and percent wxwta were 0.19 and 0.03, respectively. Heritability of grams of grain per ear and total grain yield was highest in hybrid testcrosses, with no correlation between inbreds and hybrids. The developed seedling screening method easily allowed visible drought tolerance observations in inbred lines and hybrid testcrosses but does not seem heritable in our germplasm. Epicuticular wax weight is not an ideal primary trait to evaluate for drought tolerance, but may be a good candidate to observe as a secondary trait in relation to grain yield production in hybrids. Results from this research best supports breeder selection of hybrid germplasm using seedling drought tolerance in conjunction with epicuticular wax.

Telomerase is the key enzyme synthesizing telomeric DNA in most eukaryotic organisms. In mammals, telomerase expression is abundant in the germline cells but is undetectable in most other differentiated organs. Intensive studies of telomerase have focused on human cancerous cells, where over 90% of all cancerous tissues examined have telomerase activity. In wild-type Arabidopsis, telomerase expression is abundant in reproductive organs and dedifferentiated tissues such as flowers, siliques and calli but barely detectable in vegetative tissues (both rosette and cauline leaves). In this study, a biochemical screen strategy was developed for isolation of telomerase activating mutants in Arabidopsis thaliana. Through screening of Arabidopsis activation-tagged lines by a PCR-based TRAP assay, two tac (for telomerase activator) mutants were isolated. RT-PCR analysis of AtTERT expression revealed that different mechanisms are involved in alternating telomerase activity in tac1 and tac2. We cloned and characterized the TAC1 gene. TAC1 encodes a single zinc finger protein and acts synergistically with auxin to induce telomerase expression without altering cell cycles. Telomere length was unperturbed in the mutant, but other phenotypes, such as altered root development and the ability of cells to grow in culture without exogenous auxin, indicated that TAC1 not only is part of the previously reported link between auxin and telomerase expression, but also potentiates other classic responses to this phytohormone. DNA microarrays were used to analyze the expression profile of the tac1 mutant and revealed that several drought-induced genes were up-regulated 3 to 10 fold in the tac1-1D mutant. RT-PCR analysis further confirmed this up-regulation for five of these genes. Investigation of root growth also indicated that tac1-1D roots were ~20% longer relative to wild-type. Further experiments demonstrated that over-expression of TAC1 does confer drought tolerance, but not salt tolerance. In addition, our preliminary result showed that treatment with a low concentration of IAA could induce drought tolerance in wild-type Arabidopsis. Although plants with constitutive expression of telomerase have no practical utility, the ability of TAC1 to confer drought tolerance could have significant agricultural applications.

No description available.

We compared water deficit responses of 'Tifsport', 'Tifway 419', 'Tifgreen 328', and 'MidIron' bermudagrass (Cynodon dactylon x Cynodon transvaalensis), and 'SeaSpray', 'SeaDwarf', and 'Sea Isle 1' seashore paspalum (Paspalum vaginatum Swartz) under a linear gradient irrigation system in the desert Southwest. Target irrigation levels were 100, 80, 60, and 40% (2009) and 100, 80, 70, 60, and 40% (2010) of standard reference evapotranspiration (ETo). Actual water applied (including rainfall) was 100%, 83%, 66%, and 49% of ETo (2009) and 100%, 83%, 75%, 66%, and 49% (2010). Canopy temperatures increased, and quality and dry matter production declined with reduced irrigation. For optimum turfgrass quality, 75 to 83% ETo replacement was required; for acceptable quality turfgrass, 66 to 75% ETo replacement was needed for bermudagrass, and 75 to 80% ETo for seashore paspalum. Spring green-up was delayed by drought. Bermudagrasses, particularly 'MidIron', performed better than seashore paspalums under water stress conditions.

Sorghum is the fifth most important cereal in the world and a staple food for humans. It is also a source of food and fodder for animals. In addition to the abiotic stresses such as drought, parasitic weeds of the genus Striga cause losses in sorghum production in sub Saharan Africa. Striga asiatica is a parasitic weed that attacks cereals in low input agricultural systems and is distributed throughout semi- arid regions of Africa. Most sorghum producing farmers rely on tolerance for their harvests in Striga infested fields yet the stability of tolerance in the face of a changing climate (recurrent droughts), new farming systems (mulch based agriculture) and existence of various Striga strains needs further investigation. Reduced strigolactones production was also studied as a resistance mechanism. The first study was focused on the determination of tolerance of Striga asiatica infested sorghum under drought in a pot study. Five sorghum lines were subjected to infestation with Striga and some were not infested while watering was done at 50 percent field capacity (FC) and 100 percent FC. The results showed that the five sorghum lines differed significantly in chlorophyll content and Normalised Differential Vegetation Index (NDVI). Infection did not lower chlorophyll content when it co-occurred with drought across all sorghum lines. Drought and infestation had mutually exclusive effects on chlorophyll content and NDVI. Under infestation, internode length was similar both at 100 percent FC and at 50 percent FC while under uninfested conditions, 100 percent FC gave the longer internode compared to 50 percent FC. Both infestation and irrigation regime reduced the sorghum head weight, illustrating that the two effects have synergistic effects on sorghum head weight. The second study sought to determine the effects of mulching and infestation on sorghum spp tolerance to Striga asiatica. The experiments were carried out in the seasons 2013/14 and 2014/15 summer seasons. The results indicated that mulching increased chlorophyll content in the 2014/15 season which was a drier season compared to 2013/14. In the 2014/15 season, mulching increased chlorophyll content in all varieties except Ruzangwaya, Mukadziusaende and SC Sila. When the same varieties were infested under mulch and infested without mulch, the results showed that mulching overcomes the effects of infestation in some varieties. Mulch also negates the effect of Striga parasitism and results in yield maintenance in sorghum varieties. The third study sought to determine the stability of sorghum lines when exposed to two Striga asiatica lines sourced from two places which are 500 km apart in Zimbabwe. The two strains were termed the Chiundura and Rushinga strains, based on where they were sourced. The experiments were conducted at Henderson Research Station (HRS) at Mazoe and at Bindura University of Science Education (BUSE). The results showed differential virulence for some traits while the two strains were equally virulent for some traits. The two strains were equally virulent on all sorghum lines with respect to chlorophyll content. The different sorghum lines responded differently to the effects of the two strains. The effects of the two strains were generally similar for head index, root index, and leaf index at all sites. Generally the Chiundura strain was more virulent to sorghum lines compared to Rushinga strain, confirming the existence of physiological strains of Striga in Zimbabwe. Therefore physiological speciation of Striga asiatica exists and this adds a further dimension to the complexity of Striga management in the smallholder sector. Quantification of strigolactone production by different sorghum genotypes was conducted in the laboratory using the agar gel assay. The genotype Mukadziusaende produced significantly the least (P<0.01) quantities of strigolactones, as inferred from the maximum germination distance (MGD) from the sorghum root. The MGD was negatively correlated to tiller numbers illustrating that the more the strigolactones the less the tillering capacity. Tiller numbers and MGD can therefore be used to select for reduced strigolactones production.

No description available.

>Magister Scientiae - MSc / Different nanoparticles have the ability to improve plant tolerance to drought stress. In the study we report for the first time novel morpholin-4-ium 4-methoxyphenyl (morpholino) phosphinodithioate capped- gold nanoparticles (GYY4137-capped AuNPs). The GYY4137 is a slow releasing hydrogen sulfide (H2S) donor. The GYY4137 AuNPs compared to preliminary experiments of L-serine and L-threonine gold nanoparticles. The nanoparticles were prepared using a simple reflux reduction method in a rolling boil flask at 80 oC. The uncapped GYY4137-AuNPs were relatively stable and had surface plasmon resonance at 562 nm compared to 524 nm and 560 nm of serine-AuNPs and threonine-AuNPs. The nanoparticles were capped with different concentrations (0.1-5 %) of water-soluble poly (ethylene) glycol (PEG) (Mw300) and 0.2% chitosan. The PEG did not fully encapsulate the gold nanoparticles, while the chitosan successfully produced positively charged gold nanoparticles. The formation of chitosan capped GYY4137-AuNPs were verified with UV-Visible spectroscopy (UV-Vis), High Resolution Transmission electron microscopy (HRTEM), Dynamic Light scattering (DLS) and the Zetasizer. The UV-Vis, HRTEM and STEM verified chitosan capped nanoparticles had a surface plasmon resonance peak at 560 nm, with icosahedral, tetrahedron and spherical shaped nanoparticles as the serine-AuNPs that absorb at 560 nm. The agglomerated threonine-AuNPs had a maximum absorbance peak at 524 nm. The chitosan GYY4137-AuNPs had hydrodynamic size of 347.9 nm and zeta potential of + 47 mV, while serine-AuNPs and threonine-AuNPs had hydrodynamic size of 110 nm, zeta potential of -2.9 mV and -230 mV respectively. The polydispersity index (PDI) of the chitosan capped gold nanoparticles was 0.357 compared to 0.406 of both the amino acid gold nanoparticles. The polydispersity index (PDI) showed that the nanoparticles were polydispersed nanoparticles with broad size range as confirmed by the HRTEM and STEM results/ of chitosan capped GYY4137-AuNPs. The sizes of the nanoparticles were 100 nm and 60 nm for GYY4137-AuNPs while the size serine-AuNPs were 60 nm. The gold nanoparticles structural compositions were further confirmed by energy-dispersive X-ray spectrometry (EDX) and Attenuated total reflection infrared spectroscopy (ATR-IR). EDX results proved successful gold nanoparticles synthesis by presence of the element Au in all three nanoparticles and the chitosan GYY4137-AuNPs had 48. 56 wt. % of gold. The FTIR-ATR new bands formation shows that new chemical bonds are formed between the reducing agents, the precursor gold salt solution and capping agents. The shifts showed successful encapsulation with chitosan in GYY4137-AuNPs. The chitosan encapsulation improved surface charge and reactivity of the gold nanoparticles to improve delivery of the hydrogen sulfide donor GYY4137 for later applications to plants.

Call number: LD2668 .T4 1985 M378 / Master of Science

The response of cassava (Manihot esculenta Crantz) to water stress was studied in two distinct sites (Tucson, Arizona and Santander de Quilichao, Colombia). A third experiment was conducted in Palmira, Colombia to evaluate the relationship between photosynthesis, relative humidity and yield of cassava cultivars HCol 1684. Plants stressed after 2 months of growth in Tucson reduced growth by reducing leaf formation, expansion and leaf area. Reductions in LAI due to stress imposed to MCol 1684 in Quilichao were attained by reducing leaf expansion rates and leaf formation in plants stressed after 3 months of age. Plants stressed later increased leaf fall and did not reduce leaf formation. Stress reduced dry matter production in all cultivars, especially when given to young plants. Stress also altered the patterns of dry matter partitioning in 3-month-old plants of MCol 1684, but not in those stressed at 6 months. Transpiration and diffusive conductances of MCol 1684 were reduced after 40 days of stress. These parameters were correlated to photosynthesis and leaf temperatures for non-stressed plants, and additionally with relative humidity in the plants stressed after 3 months of growth. Interestingly, leaf temperatures were lower in stressed plants of MCol 1684, which suggests that stressed cassava plants can avoid excessive heating caused by stomatal closure simply changing leaf orientation and increasing reflectance. Leaf water potential was slightly reduced by stress in Tucson except for MVen 218. Stressed plants of MCol 1684 in Quilichao showed lower values of (L) than those of non-stressed plants after 30-40 days of treatment, suggesting an adaptation of stressed plants acquired during the stress period. The effects of air humidity on stomatal functioning of MCol 1684 seems to be strong as suggested by the dependence of transpiration, conductances and photosynthesis on relative humidity.

This study sought to determine the effects of reselection on the adaptation of a grain sorghum (Sorghum bicolor (L.) Moench) population to heat and drought. A random-mating population, NP9BR, was subjected to selection under heat and moisture stress for nine generations to improve its resistance to drought. One hundred single plants selected from the original (C₀) and the reselected (C₉) population were grouped by maturity and evaluated for drought resistance by measuring morphological and agronomic characters under wet (normal irrigation) and dry (restricted irrigation) conditions at the University of Arizona, Marana Agricultural Center, Arizona. Eighty of the selections were grown under a sprinkler irrigation gradient system at Yuma Mesa Agricultural Center, Arizona. Selection under drought conditions reduced plant height, head exsertion, leaf width and length, and seed weight of the population. Blooming was evened out from predominantly early in C₀ to early, medium and late maturing in C₉. Moisture stress reduced grain yield by an overall 16%. The medium maturing selections suffered less yield reduction than the early and late. Although C₉ progenies showed a greater reduction in grain yield, several of them produced equal yields in wet and dry treatments. Leaf width and length were significantly correlated (p = .1%) with yield under dry conditions in all maturity groups. Most selections with very short narrow leaves had small heads and low yields. Some with medium leaf width and length out-yielded broad-leaved ones especially under dry conditions. Forty percent of the selections from C₉ had good head production characteristics under the irrigation gradient system, compared to only 20% from C₀. There were four times as many selections in C₀ unable to produce heads under the system as there were in C₉. The majority of genotypes with good head production in both populations came from the early maturing group. The highest grain yields came from C₀ selections but some C₉ selections with comparable yields were observed. This study indicates that phenotypic selection may still have potential for isolating high-yield genotypes from random-mating populations but may be inadequate for separating differences in drought tolerance among genotypes.