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Water was withheld from 2-year-old seedlings or rooted cuttings of four birch genotypes (Betula alleghaniensis Britton, B. davurica Pall., B. nigra L. ‘Cully’, and B. papyrifera Marsh.) until the combined weight of the container and plant decreased below 40% of its original value to induce plant predawn water potential between −1.5 MPa and −2.1 MPa, after which plants were supplied with a requisite amount of water to reach 40% of its original value for 5 weeks under controlled conditions to investigate changes in gas exchange, osmotic solutes, leaf abscission, and growth compared with well-watered (WW) plants. Observations indicated that three of the four genotypes (except B. papyrifera) expressed three stages of photosynthetic response during water deficit: 1) a stress stage, 2) an acclimation stage, and 3) an adapted (or tolerance) stage. The stages were characterized by decreasing, increasing, and stabilized Pnws/ww (net photosynthesis presented as a ratio of water-deficit stressed (WS) plants to WW plants), respectively. A strong relationship between Pn and g S observed in the WS plants of the four genotypes, suggested inhibition of Pn by stomatal closure. After exposure to water deficit for 5 weeks, Pnws/ww recovered to 70% of the initial value for B. alleghaniensis and B. nigra ‘Cully’ and 98% for B. davurica and B. papyrifera. WS plants had higher foliar concentrations of chlorophyll a and b (nmol/g) and potassium (%) than the WW plants. Increased levels of polyols (mg/g) were detected only in the WS plants of B. allegahaniensis. Increased levels of carbohydrates or organic acid under water deficit were not detected. A significant increase in leaf abscission in the WS plants of B. papyrifera compared with the other genotypes could be a morphological adaptation to water deficit conditions and facilitate recovery of Pnws/ww during the acclimation stage.
Orchards established on weathered, acidic mineral soils in the Ozark Highlands must be managed to meet tree nutritional requirements. However, a common characteristic of Ozark Highland soils is a relatively low soil organic matter (SOM) concentration, a condition that can have detrimental effects on orchard productivity. Organic orchard management poses specific challenges to managing competitive under-tree vegetation and supplying appropriate supplemental nutrition to maintain tree growth and cropping. In Mar. 2006, an experimental apple orchard was established to evaluate the effects of under tree, in-row groundcover management system (i.e., shredded paper, wood chips, municipal green compost, and mow-blow), and nutrient source (i.e., non-fertilized control, composted poultry litter, and pelletized organic commercial fertilizer) on SOM, carbon (C), and nitrogen (N) concentration, and soil C and N sequestration over time in an organically managed orchard in the Ozark Highlands region of northwest Arkansas. Soil organic matter, total C, and total N concentrations (soil weight basis) and contents (area basis) in the top 7.5 cm increased in all groundcover management systems from 2006 to 2011. The greatest differences were observed with municipal green compost treatments. Significant interactions between groundcover management treatment and nutrient source were only observed for SOM concentration, whereas nutrient source did not affect total C and total N concentrations or contents. Soil C sequestration rates were 0.9, 1.0, and 2.8 Mg·ha−1 per year under the shredded paper, wood chip, and green compost treatments, respectively, whereas total C content did not change over time under the mow-blow treatment. The green compost treatment was the only treatment that had significant total N sequestration occur (0.25 Mg nitrogen/ha/year). Results of this study indicate that organic cultural methods can significantly augment near-surface soil C and N contents, which will likely increase productivity, of apple orchards in the Ozark Highlands over a relatively short period time after establishment. This study has implications for orchards in similar soils or environmental circumstance and for both organic and conventional management systems.
The broad mite (Polyphagotarsonemus latus) was found in association with leaf-curling symptoms on primocane-fruiting blackberry (Rubus rubus) in Arkansas in 2007–2009. Broad mite had not been previously reported on blackberry. The plots sampled in this study were part of a study comparing harvesting in the fall versus harvest in spring and fall, high tunnels versus ambient conditions, and three genotypes, all under organic production. Leaves were sampled, broad mites per leaf counted, and leaf area and trichome density measured. Results indicated that broad mite is capable of overwintering in a moderate temperate climate and that it reduces leaf area of primocane-fruiting blackberry. The fall-only harvest system had fewer broad mites than fall and spring harvest. There were a range of genotype effects on broad mite populations, including one genotype, ‘Prime-Jan®’, on which broad mite populations remained low, and one genotype, APF-46, on which mite populations grew significantly. Observations indicate that the broad mite may be a pest of ‘Prime-Ark® 45’, another primocane-fruiting cultivar.
Abstract
Spur leaf and fruit characteristics at harvest were measured near the central leader at 1, 2, and 3 m above ground on 17-year-old trees of ‘Oregon Spur Delicious’ apple (Malus domestica Borkh.). Percentages of full sunlight at 1 (bottom), 2 (middle), and 3 m (top) positions were 9, 23, and 48, respectively. Vegetative spurs at the top had greater average leaf dry weight, total leaf number, leaf area, leaf dry weight per spur, specific leaf weight (SLW), and bud diameter than spurs at the bottom. Fruiting spurs at the top had greater leaf dry weight, leaf dry weight per spur, SLW, bud diameter, and spur length than spurs at the bottom. Vegetative spurs had greater values than fruiting spurs for all spur traits except leaf number per spur. Fruit weight, size, and soluble solids were greater at the top than at the bottom. Fruit at the bottom had higher firmness and levels of starch, N, P, K, Zn, Ca, Fe, B, and Mg. SLW, leaf dry weight per spur, and average leaf dry weight of vegetative and fruiting spurs were correlated with percentage of full sunlight. Fruit size, weight, soluble solids, starch, and N content also were correlated with percentage of full sunlight. SLW was correlated with fruit size, weight, soluble solids, and starch, and N, P, Mg, Ca, and Fe content.
Southern organic fruit production is limited by a lack of regionally appropriate, scale-neutral, and market-focused research and technology. There has been limited research, outreach, and cooperation among universities on organic fruit crops in the southern region. Organic research and outreach activities, based on producer input, must be focused on the most limiting areas of the organic system in order to allow southern producers to receive the economic and environmental benefits that organic agriculture can provide. With funding from USDA-SARE and USDA-SRIPMC, researchers at the University of Arkansas have collaborated with scientists, extension specialists, growers, and representatives of the organic industry in Arkansas, Georgia, Kentucky, North Carolina, South Carolina, and Tennessee to create a Southern Region Organic Fruit Working Group (SROFWG). The SROFWG conducted in-state focus group meetings through which barriers to production and marketing, and opportunities for organic fruit in the region were identified. Prioritized research and outreach needs that were identified in the focus groups included use and understanding of organic fertilizers and nutrient management; methods, knowledge and awareness of pest disease and weed control including orchard floor management; information on transition to organic; consumer awareness and market development and the economics of organics. The planning activities of the SROFWG support the development and submission of grants for cooperative and collaborative research and outreach programs to sustain and expand organic fruit production in the southern region.
Breeding heat-tolerant spinach is an important project to meet the demand of increasing spinach production in heat conditions. Seed germination is the early stage to test, screen, and develop heat-tolerant spinach genotypes. The objective of this research was to determine temperature effect on the seed germination percentage and to select heat-tolerant spinach genotypes. A total of nine spinach genotypes were used in this research. The germination experiment was conducted using seven temperatures: 10, 15, 20, 25, 30, 32, and 35 °C under growth chambers. The temperature trials were conducted using completely randomized design (CRD) with three replicates. Spinach seed germination percentage varied among the nine spinach genotypes under the seven temperatures, indicating that genetic variation for heat tolerance existed in the nine spinach genotypes. ‘Donkey’, ‘Marabu’, and ‘Raccoon’ showed higher seed germination percentage with over 70% at 30 and 32 °C, indicating the three spinach genotypes had heat tolerance for germination. However, all spinach genotypes except ‘Ozarka II’ dropped their germination percentages sharply to less than 30%; ‘Ozarka II’ had 63% germination under 35 °C, indicating it is a good source of heat tolerance for seed germination. The higher germination percentages above 30 °C of ‘Ozarka II’, ‘Donkey’, ‘Marabu’, and ‘Raccoon’ may indicate their potential as donors of heat-tolerant traits in spinach breeding program.
Strawberry (Fragaria ×ananassa) production practices followed by growers in the United States vary by region. Understanding the challenges, needs, and opportunities in each region is essential to guide research, policy, and marketing strategies for the strawberry industry across the country, and to enable the development of general and region-specific educational and production tools. This review divided the United States into eight distinct geographic regions and an indoor controlled or protected environment production system. Current production systems, markets, cultivars, trends, and future directions for each region are discussed. A common trend across all regions is the increasing use of protected culture strawberry production with both day-neutral and short-day cultivars for season extension to meet consumer demand for year-round availability. All regions experience challenges with pests and obtaining adequate harvest labor. Increasing consumer demand for berries, climate change-induced weather variability, high pesticide use, labor and immigration policies, and land availability impact regional production, thus facilitating the adoption of new technologies such as robotics and network communications to assist with strawberry harvesting in open-field production and production under controlled-environment agriculture and protected culture.