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Seedlings of eight Prunus taxa were evaluated for variation in susceptibility to a single, 4- or 5-day flooding period and root rot caused by Phytophthora cryptogea Pethybr. & Lafferty. Survival, plant defoliation, disease severity index, root necrosis, and net photosynthesis indicated that the combination of flooding and pathogen was significantly more severe to all taxa than either individual treatment. Most response variables reflected early plant dysfunction but were not correlated with long-term survival. Long-term survival was 70% in the combination treatment compared to 99% in the control group. Flooding injured seedlings more than the pathogen in most taxa. Taxa differed only slightly in tolerance to the treatments, as measured by survival rate. Prunus takesimensis Nakai had the highest survival rate of 100% and along with P. mahaleb L. and P. yedoensis Matsum. showed some tolerance to flooding and the pathogen. Prunus sargentii Rehd. had the lowest survival rate of 81% and appeared to be least tolerant to the pathogen.
Since 1977, it was believed the grape strain of Xylella fastidiosa, Pierce's Disease (PD), was limited to sites receiving less than 800 hours of winter chilling below 45 °F. Warm winters since 1992–93 resulted in numerous PD-positive vineyards in central Texas which were previously nonaffected. Vine mortality ranges from minimal to over 80% dead vines. A Davis Mountains site receiving over 1,000 hours was also severely infected in 1996. The last severe winter in Texas was 1989–90; therefore, warm winters could be contributing. This climatic change could have affected vines, vectors, bacteria, and/or hosts. Recent work based on a study of 20 PD samples, 11 from Texas and 9 from other states, including California and Florida, indicates that the samples of PD grape strain of Xylella fastidiosa are clonally related. ELISA tests failed to identify PD from 1994–96; therefore, a sensitive REP-PCR test is needed before vine, bacteria, vector, and host management strategies can be developed.
Abstract
Trees of Malus domestica (Borkh.) ‘Miller Sturdeespur’ were hand thinned to achieve light, medium, and heavy fruit loads. A heavy European red mite (ERM), Panonychus ulmi (Koch), infestation was encouraged by mite seeding and predator elimination in half the trees for each fruit load. The effect of these treatments were determined on fruit number, number and percentage of drops, fruit size, color, soluble solids, titratable acidity, pH, firmness, and percentage of foliar concentration for 5 macronutrients. Mite feeding increased the percentage of drop and reduced red pigmentation, soluble solids, and leaf phosphorus and calcium. Deleterious effects of mite feeding increased with increasing fruit load. With light fruit loads, heavy mite feeding had a negligible effect on fruit quality.
Although transplanted trees typically establish and grow without incident in frequently irrigated turfgrass, their performance in precisely irrigated turfgrass in an arid climate is not known. We investigated the effect of precision irrigation scheduling on growth and water relations of balled-and-burlapped littleleaf linden (Tilia cordata Mill. `Greenspire') planted in buffalograss (Buchloë dactyloides [Nutt.] Engelm. `Tatanka') and kentucky bluegrass (Poa pratensis L.). Over 2 years, trees in turfgrass were irrigated either by frequent replacement based on local reference evapotranspiration, or precision irrigated by estimating depletion of soil water to the point of incipient water stress for each turfgrass species. Predawn leaf water potential and stomatal conductance of trees were measured during first-year establishment, and predawn leaf water potential was measured during a mid-season water-deficit period during the second year. Trunk diameter growth and total tree leaf area were measured at the end of each year. Values of predawn leaf water potential and stomatal conductance of trees in precision-irrigated buffalograss were lower (–0.65 MPa, 25.3 mmol·m–2·s–1) than those of trees in the other treatments near the end of the first growing season. The longer interval between precision irrigations resulted in mild water stress, but was not manifested in growth differences among trees across treatments during the first season. During the water-deficit period of the second year, there was no evidence of stress among the trees regardless of treatment. At the end of the second season, total leaf area of trees grown in precision-irrigated kentucky bluegrass (1.10 ± 0.34 m2) was 46% of that of trees grown in buffalograss (2.39 ± 0.82 m2) that were irrigated frequently. Trunk diameter growth of trees in frequently irrigated kentucky bluegrass (1.91 ± 2.65 mm) was 29% of that of the trees grown in buffalograss (6.68 ± 1.68 mm), regardless of irrigation treatment, suggesting a competition effect from kentucky bluegrass. We conclude that frequent irrigation of balled-and-burlapped trees in turfgrass, particularly buffalograss, is more conducive to tree health during establishment than is maximizing the interval between turfgrass irrigation. Regardless of irrigation schedule, kentucky bluegrass appears to impact tree growth severely during establishment in an arid climate.
The effect of irrigation management strategies on the quality and storage performance of `O'Henry' peaches [Prunus persica (L.) Batsch] was studied for two seasons. The deficit irrigation treatment induced a higher fruit soluble solids concentration and lower fruit weight. The excess irrigation treatment, compared to the optimum treatment, increased the rate of fruit water loss without altering fruit quality and storage performance. Scanning electron microscope observations indicated a higher density of trichomes on fruit from the deficit and optimum irrigation treatments than from the excess irrigation treatment. Light microscopy studies indicated that fruit from deficit and optimum irrigation had a continuous and much thicker cuticle than fruit from the excess irrigation treatment. These differences in exodermis structure may explain the high percentage of water loss from fruit from the excess irrigation treatment compared to the deficit and optimum irrigation treatments.
We have been examining the response of maize seedling roots to oxygen stress. Previously, we have shown that maize seedlings with primary root lengths of 10cm or greater require a pretreatment with low oxygen (hypoxia) for survival of greater than 12 hours of anoxia. During the pretreatment there is induction of mRNA and increase in enzymatic activity of alcohol dehydrogenase (ADH) and other enzymes that are necessary for alcoholic fermentation. However, we have found that younger seedlings do not need a pretreatment to survive anoxia. They appear to have high levels of ADH and other enzymes that are needed for anaerobic survival at levels equivalent to those that are induced in older seedlings. These results suggest that, at the time of seedling emergence, seedlings may be more adapted to oxygen stress than during later stages of growth.
Management of agricultural irrigation water is extremely important as fresh water resources are being depleted on a global scale. In anticipation of regulatory restrictions, several greenhouse and nursery operations in New Jersey have implemented systems that disinfect and recycle their irrigation water. This study compared the disinfection methods at two greenhouses and three container nurseries, focusing on the qualitative and quantitative benefits of using chlorine gas, ultraviolet light, ozone, and copper for water disinfection. The data were collected during on-site visits where the growers were interviewed on camera. A cost analysis was performed, but the most efficient disinfection technique could not be determined due to the variability between businesses and various unquantifiable benefits of proactive water management recycling, such as improved plant health, decreased fungicide and fertilizer use, a cleaner operation, reduced runoff, reduced pressure on aquifers, and increased customer satisfaction. The investment and maintenance costs per hectare and 1000 L were calculated, which can be useful reference tools for growers. The net present value (NPV) of each disinfection system was calculated to analyze the profitability of the investments. All three container nurseries had positive NPV values and profitable investments, which improved with cost sharing from the National Resource Conservation Service. This information will be useful in the future as growers throughout the state, and country, may be required to deal with the stricter regulation of their irrigation runoff.
Water used for peach irrigation can be reduced by supplying less than full evapotranspiration (ET) during a specific period of fruit growth (RDI). The effect of RDI technique of fruit quality, internal breakdown and storage performance was studied on `O'Henry' during the 1990, 1991 and 1992 seasons. The three irrigation regimes (50, 100 and 150% ET) imposed during the three seasons induced a higher soluble solids content in the fruit without reduction of postharvest life. Scanning and light microscope observations indicated a modification of cuticle and epidermal characteristics by the three irrigation treatments. These differences in exodermis structure may explain the lower percentage of water loss on fruit from the under irrigated (50% ET) compared to well irrigated (100% ET) and over irrigated (150% ET) treatments during the three seasons.
Differences in soil microenvironment affect the availability of N in small areas of large turfgrass stands. Optical sensing may provide a method for assessing plant N needs among these small areas and could help improve turfgrass uniformity. The purpose of this study was to determine if optical sensing was useful for measuring turfgrass responses stimulated by N fertilization. Areas of `U3' bermudagrass [Cynodon dactylon (L.) Pers.], `Midfield' bermudagrass [C. dactylon (L.) Pers. × C. transvaalensis Burtt-Davy], and `SR1020' creeping bentgrass (Agrostis palustris Huds.) were divided into randomized complete blocks and fertilized with different N rates. A spectrometer was used to measure energy reflected from the turfgrass within the experimental units at 350 to1100 nm wavelengths. This spectral information was used to calculate normalized difference vegetation index (NDVI) and green normalized difference vegetation index (GNDVI). These spectral indices were regressed with tissue N and chlorophyll content determined from turfgrass clippings collected immediately following optical sensing. The coefficients of determination for NDVI and GNDVI regressed with tissue N averaged r 2 = 0.76 and r2 = 0.81, respectively. The coefficients of determination for NDVI and GNDVI regressed with chlorophyll averaged r 2 = 0.70 and r 2 = 0.75, respectively. Optical sensing was equally effective for estimating turfgrass responses to N fertilization as more commonly used evaluations such as shoot growth rate (SGR regressed with tissue N; r 2 = 0.81) and visual color evaluation (color regressed with chlorophyll; r 2 = 0.64).