St. augustinegrass (Stenotaphrum sp.) is a warm-season perennial turfgrass that grows widely in tropical regions around the world. St. augustinegrass is valued for both its turf performance and high levels of resistance to biotic and abiotic stresses. The current study was aimed at developing nuclear microsatellite markers for st. augustinegrass. Pyrosequencing of an enriched microsatellite library on the Roche FLX platform using a 454 Titanium kit produced 57,306 sequence reads; 2614 of which contained short tandem repeats. One hundred primer pairs were tested with 18 accessions from the U.S. Department of Agriculture National Plant Germplasm System st. augustinegrass collection grown in Griffin, GA. This collection contains both Stenotaphrum dimidiatum and Stenotaphrum secundatum accessions. Among revealed 100 primer pairs, 33 were polymorphic. A total of 175 alleles were amplified. The number of observed alleles per primer pair ranged from two to 10, with an average of 5.3. Shannon’s information index and Nei’s genetic diversity values were 0.4403 and 0.2873, respectively. This set of microsatellite markers is useful for assessment of genetic diversity and construction of molecular genetic linkage maps in st. augustinegrass.
Zhiyong Wang, Paul Raymer, and Zhenbang Chen
Diana Carolina Núñez-López, Augusto Ramírez-Godoy, and Hermann Restrepo-Díaz
The bean crop is of great importance for human consumption as a source of protein. One of the most limiting insect pests of this crop in Colombia is the whitefly, Trialeurodes vaporariorum (Westwood). Currently, various nonchemical pest control alternatives for cleaner production are being sought. This study aimed to determine the influence of kaolin on the development of populations of whitefly in greenhouses, and its effect on the physiological characteristics of the bean crop [Phaseolus vulgaris (L.)]. This work was conducted in the greenhouses of the Universidad Nacional de Colombia, in Bogotá. Three experiments were carried out and four treatments were evaluated: 1) control (without any insecticide), 2) synthetic chemical insecticides, and foliar applications of kaolin at 3) 2.5%, and 4) 5% (W/V). Generally, the results showed a high percentage of efficacy (≈91%) on whitefly control in plants treated with 5% kaolin, compared with the plants not treated with insecticides in the three different experiments. In addition, foliar applications of kaolin decreased transpiration by 40% and enhanced by 43% the contents of leaf chlorophyll without affecting bean yield. In conclusion, the use of kaolin particle can be considered as an alternative tool in a program of agricultural management on the bean crop since it can control a high percentage of whitefly and it may help the plant physiology, especially under conditions of abiotic stress such as drought stress.
James W. Cross, Stacy A. Bonos, Bingru Huang, and William A. Meyer
Heat and drought are two major abiotic stresses causing a decline in quality in cool-season turfgrasses during the summer. The objectives of this study were 1) to determine whether genotypic variations in turf performance during summer stress in New Jersey is related primarily to heat tolerance or drought tolerance of tall fescue; and 2) to make selections of plants tolerant to summer stress for breeding efforts. Twenty-four tall fescue genotypes exhibiting differential performance during summer months in field conditions (12 summer stress-tolerant and 12 summer stress-sensitive) were selected from the germplasm pool present at the New Jersey Agricultural Experiment Station. Plants of these 24 genotypes were exposed to heat, drought, or heat + drought. There were generally no significant differences in turf quality, photochemical efficiency, relative water content, or electrolyte leakage between summer stress-tolerant and -sensitive genotypes, except in the heat treatment in which the summer stress-tolerant selections performed significantly better. The results indicate that the superior performance of the summer stress-tolerant plants under field conditions is mainly the result of superior heat tolerance.
Wayne H. Loescher, Paolo Sabbatini, Guo-Qing Song, Kenneth Sink, and James Flore
Mannitol, a sugar alcohol that appears to serve as an osmoprotectant/compatible solute to cope with salt stress, is synthesized in celery (Apium graveolens L.) via the action of a NADPH dependent mannose-6-phosphate reductase (M6PR). To evaluate the abiotic stress effects of mannitol biosynthesis, we transformed celery with an antisense construct of the celery leaf M6PR gene under control of the CaMV 35S promoter. Unlike wild type (WT) celery, independent antisense M6PR transformants did not accumulate significant amounts of mannitol in any tissue, with or without salt stress. In the absence of NaCl, and despite the lack of any significant accumulation of mannitol that is normally the major photosynthetic product, antisense transformants were mostly phenotypically similar to the WT celery. However, in the presence of NaCl, mature antisense transgenic plants were significantly less salt-tolerant, with reduced growth and photosynthetic rates, and some transformant lines were killed at 200 mM NaCl, a concentration that WT celery can normally withstand. Although mannitol biosynthesis is normally enhanced in salt-treated WT celery, no such increase was observed in the antisense transformants. Like our previous gain of function results showing enhanced salt tolerance in Arabidopsis plants transgenic for a sense M6PR construct, these loss of function results, using an antisense construct in celery, demonstrate a major role for mannitol biosynthesis in developing salt-tolerant plants.
Kathryn Pickle, Rajasekaran Lada, Claude Caldwell, Jeffrey Hoyle, and Jeffrey Norrie
Consumer demand for chemically free produce has increased; however, producers have become increasingly dependent on unreliable chemical defenses for control of diseases and pests. These dilemmas, along with the desire to maintain healthy farmland, have led to the research and development of environmentally sound practices. It is hypothesized that predisposing plants to photo, physical, and mechanical (PPM) mechanisms can allow plants to better withstand stress. Plants exposed to one form of PPM mechanism could confer resistance to a range of biotic and abiotic stresses. Such cross-resistance is commonly seen, but not well-understood. In this study, various PPM factors, including UV-C radiation, leaf brushing, and canopy trimming, were applied to field-grown carrots (Daucus carotae L.). The degree of blight and white mold infection was measured. Preliminary analyses showed that UV-C radiation at 4 weeks post-emergence or brushing at 4 or 8 weeks significantly reduced carrot blight and/or white mold. This implies that certain PPM mechanisms may induce plant defenses, allowing the crop to better defend itself against future biotic stress.
Hrvoje Rukavina, Harrison Hughes, and Yaling Qian
Freezing is the major abiotic stress that limits geographical distribution of warm-season turfgrasses. Prior studies have indicated variation in freezing tolerance in saltgrass clones. Therefore, this 2-year study examined the freezing tolerance of 27 saltgrass clones as related to collection sites in three zones of cold hardiness. Furthermore, these clones were evaluated for time of leaf browning in the fall with the intent to determine if there was a correlation between this trait and freezing tolerance. Rhizomes were sampled during 2004 and 2005 midwinters from clones established in Fort Collins, Colo., and then subjected to a freezing test. Saltgrass freezing tolerance was highly influenced by the climatic zone of clone origin in both years of the experiment. Clones with greater freezing tolerance turned brown earlier in fall in both seasons. Ranking of zones for the average LT50 was: zone 4 (–17.2 °C) < zone 5 (–14.4 °C) < zone 6 (–11.1 °C) in 2004 and zone 4 (–18.3 °C) < zone 5 (–15.7 °C) < zone 6 (–13.1 °C) in 2005. Clones from northern areas tolerated lower freezing temperatures better overall. This confirmed that freezing tolerance is inherited. Large intraspecific variation in freezing tolerance may be effectively used in developing cold-hardy cultivars.
Matthew A. Jenks, Carole H. Gaston, Mark S. Goodwin, Jessie A. Keith, Rebecca S. Teusink, and Karl V. Wood
Cuticular waxes were analyzed on abaxial and adaxial leaf surfaces of three Hosta genotypes differing in leaf surface glaucousness; the glossy-leaved Hosta plantaginea, the glossy-leaved Hosta lancifolia, and the glaucous-leaved Hosta `Krossa Regal'. All three hosta had their highest total leaf wax quantity in the spring soon after full leaf expansion. The major wax constituent class on these hosta was primary alcohols, comprising up to 84.6% of the total wax. Many hosta leaves had unusually high C24 length primary alcohols, especially in the spring. However, the dominant chain length in this alcohol class varied with development and genotype. A unique class of ß-diketones were present on the glaucous `Krossa Regal', comprising as much as 28.7% of the total waxes on abaxial leaf surfaces in the summer. Interestingly, these ß-diketones were only 0.9% of total waxes on adaxial leaf surfaces of `Krossa Regal' in the summer. Studies are under way to determine whether the dramatic seasonal changes in the waxy leaf coatings described in this report are associated with biotic and abiotic stress resistance in hosta.
Madhulika Sagaram and Leonardo Lombardini
Pecan is a riparian species distributed over an area of geographic and climatic variation; such a wide distribution produces exposure to varied environmental conditions, providing a potential for genetic adaptation within the cultivars. Genotypes can be screened in order to obtain more drought tolerant cultivars using indirect screening parameters (chlorophyll fluorescence, osmotic adjustment, and abscisic acid assay) based on physiological responses of plants to abiotic stress conditions. A study was established at Texas A&M University, College Station, using a mixture of fritted clay (Quick dry) and pure sand in 1:1 (by weight) ratio to study the effects of drought on pecan rootstocks. The experiment was set up with the three water potential levels as treatments (–0.033 MPa, –0.1 MPa, –0.3 MPa) in a randomized complete-block design with three blocks. Measurements will include leaf water relations (relative water content, leaf water potential, osmotic adjustments, etc.), gas exchange parameters [net carbon dioxide assimilation rate (A), transpiration rate (E), stomatal conductance (gs)], chlorophyll fluorescence measurements [minimum (Fo), maximum (Fm), and variable fluorescence (Fv), quantum efficiency], water use efficiency, and abscisic acid assay on roots. Statistical analysis systems (SAS) package will be used for analysis. PROC GLM of the SAS will be used for statistical analysis of study involving plant response to water potential levels.
Dharmalingam S. Pitchay, John Gray, Jonathan M. Frantz, Leona Horst, and Charles Krause
Geranium (Pelargonium ×hortorum) typically follows the C3 metabolic pathway. However, it switches to CAM metabolism under certain abiotic stress environments. This switch may affect the nutritional requirement and appearance of visible deficiency symptoms of these plants. Because potassium (K) plays a key role in stomatal function, K-deficiency was studied in geranium. Plants were grown hydroponically in a glass greenhouse. The treatments consisted of a complete, modified Hoagland's solution with millimolar concentrations of macronutrients, 15 NO3-N, 1.0 PO4-P, 6.0 K, 5.0 Ca, 2.0 Mg, and 2.0 SO4-S and micromolar concentrations of micronutrients, 72 Fe, 9.0 Mn, 1.5 Cu, 1.5 Zn, 45.0 B, and 0.1 Mo, and an additional solution devoid of K. It took longer to develop the classic K deficiency symptoms than other bedding plant species commonly require. The K-stress plants' dry weight was 10% and 37% of control at incipient and advanced stage, respectively. When portions of geranium leaves were covered, symptomology on leaves with K stress developed rapidly (within 2 days) compared to the uncovered portion of the leaf blade. Control plants contained an abundance of marble-shaped K crystals in the adaxial surface of leaf mesophyll, but were lacking in the K-deficient plants. Geranium is more prone to K stress during short days than long days and an additional supply of K would be needed for normal growth in short days.
James F. Cahill and Eric G. Lamb
A plant's performance depends on its ability to deal with numerous, simultaneous ecological challenges. In both natural and production systems, dominant challenges include competition for soil resources and light, herbivory, and general abiotic stress. A central goal of research is to understand how these processes interact with each other and with plant phenotype (above- and belowground) to influence overall plant performance. Complicating these efforts is the reality that plants are phenotypically plastic with the phenotypic response to one challenge potentially altering the impact of a different challenge. Furthermore, factors external to the plant (e.g., the genotypic and phenotypic composition of the surrounding plants) can also influence the consequence of various ecological pressures. We have been using Arabidopsis thaliana as a model organism to help disentangle this complicated web of ecological interactions. Competitive ability can be influenced by small genotypic changes. A plant's ability to suppress competitors is driven mainly by size-related traits and soil fertility and a plant's ability to withstand harm coming from numerous sources. The relative importance of competition is contingent not only on the match between genotype and environment, but also on the diversity of genotypes within a given population. There is a need to consider alternative effects of plant traits along with the cascading consequences of plant responses to biotic and abiotic challenges.