Conifers represent a sizeable portion of nursery and landscape sales in the upper midwestern U.S. Several conifer species have been overplanted to the point where disease problems and insect pressures have developed. Although more than 40 true fir (Abies Mill.) exist throughout the northern hemisphere, use of firs in the landscape and Christmas tree industry has been limited to relatively few species. This is largely due to perceived intolerance of many site conditions. However, recent research suggests Abies are more tolerant of varying site conditions than originally thought. Successful introduction of new exotic fir species for landscape use will require a systematic approach to identify species that are adapted to environmental stresses. In this article we review the extent and nature of inter-specific variation among Abies species in traits commonly associated with tolerance of stresses found in the upper midwestern U.S. Specifically, we focus on cold hardiness, budbreak, photosynthetic gas exchange and water relations, and response to soil pH. It is important to match plants possessing necessary adaptive characteristics with the existing site conditions. Therefore, multiple screening factors should be met when identifying species or trees from different provenances for future introduction.
G.E. Jones and B.M. Cregg
Todd Rosenstock and Patrick Brown
Alternate bearing exerts economic and environmental consequences through unfulfilled yield potential and fertilizer runoff, respectively. We will discuss a systematic biological–statistical modeling management integration approach to address the concert of mechanisms catalyzing alternate bearing. New engineering technologies (precision harvesting, spatially variable fertigation, and mathematical crop modeling) are enabling optimization of alternate bearing systems. Four years of harvest data have been collected, documenting yield per tree of an 80-acre orchard. These results have shown variability within orchard to range from 20–180 lbs per tree per year. Results indicate irregular patterns not directly correlated to previous yield, soil, or tissue nutrient levels, or pollen abundance. Nor does significant autocorrelation of high or low yields occur throughout the orchard, suggesting that genetically dissimilar rootstocks may have significant impact. The general division of high- and low-yielding halves of the orchard may infer a biotic incongruency in microclimates. This orchard does not display a traditional 1 year-on, 1 year-off cyclic pattern. Delineation of causal mechanisms and the ability to manage effectively for current demands will empower growers to evaluate their fertilization, irrigation, male: female ratio, site selection, and economic planning. In comparison to annual crops, the application of precision agriculture to tree crops is more complex and profitable. When applied in conjunction, the aforementioned methods will have the ability to forecast yields, isolate mechanisms of alternate bearing, selectively manage resources, locate superior individuals, and establish new paradigms for experimental designs in perennial tree crops.
Stan C. Hokanson, Phil L. Forsline, James R. McFerson, Warren F. Lamboy, Herb S. Aldwinckle, and Aimak D. Djangaliev
Malus sieversii, the main progenitor of domesticated apple, is native to areas in Central Asia. To better represent Malus wild germplasm in the USDA–ARS germplasm collections, maintained in Geneva, N.Y., a cooperative project was initiated with the Republic if Kazakhstan to collect and assess that country's wild populations of M. sieversii and to develop more secure in situ reserves to complement ex situ holdings in the United States and Kazakhstan. To date, four exploration trips to the region have included participants from the United States, Kazakhstan, Canada, New Zealand, and South Africa. Four Kazkh scientists have toured USDA–ARS sites, exchanged information, and collected germplasm in the United States greenhouse screens of 1600 have revealed potentially new sources of resistance to apple scab, cedar apple rust, and fire blight. An isozyme analysis of maternal half-sib families from four regions suggests the populations of M. sieversii collected represent a single panmictic population, with over 85% of total genetic variation due to differences among families. The most recent collections in 1995 were directed towards more ecologically diverse regions, including a site (Tarbagatai) at the most northern limit for M. sieversii equivalent to northern Minnesota in the United States. Some trees in this region produced fruit nearly 70 mm in diameter with excellent aroma, firmness, and color. This germplasm is being systematically characterized for horticultural traits, pest and disease resistance, and molecular markers.
Philip L. Forsline, Warren F. Lamboy, James R. McFerson, and Cecil Stushnoff
The USDA–ARS germplasm collection of cold-hardy Vitis held at the Plant Genetic Resources Unit, Geneva, N.Y., has over 1300 clonal accessions maintained as field-grown vines. Security back-up using field-grown or potted vines at remote sites or via in vitro methods is costly. Cryopreservation offers a safe, cost-effective alternative. While we routinely employ cryogenic storage of dormant buds of Malus, dormant buds of Vitis generally do not appear to tolerate the desiccation levels required by our current cryopreservation protocol. Since tolerance to desiccation and cold appear to be correlated in Vitis, we tested desiccation tolerance of 60 germplasm accessions selected from the core subset to represent a range of cold hardiness. Budwood was collected in December 1995 in Geneva, stored at –4°C in sealed bags, and systematically desiccated to 30% and 20% moisture. In some treatments, additional desiccation was imposed by slow freezing to –25°C. Microscopic examination of rehydrated buds indicated 60% of accessions tolerated desiccation as low as 20% moisture. Freeze-desiccation at –25°C after desiccation at –4°C neither increased nor decreased viability in these accessions. Only slight modification so current protocols should be necessary for cryopreservation of this class. Of the remaining accessions, 25% tolerated desiccation to 30% moisture, but 15% were intolerant to any desiccation level tested. Techniques must be developed to successfully cryopreserve both these classes of accessions.
Patrick J. Conner
Germination of muscadine seed has frequently been low and irregular in the University of Georgia breeding program. A systematic study was undertaken to determine the best seed treatments and germination conditions for muscadine seed. Open-pollinated seeds of ‘Fry’ muscadine were used for all treatments. Stratification of seeds was performed by placing dry seed in damp vermiculite at 4 °C for periods of 0, 30, 60, and 90 d. The 90-d stratification period gave the highest germination percentage, with successively lower germination in the shorter stratification treatments. Pretreatment of seeds before stratification with three rates (0.5, 1.0, and 2.0 M) of hydrogen peroxide (H2O2) and four rates (1, 2, 4, and 8 g·L−1) of gibberellic acid (GA3) were used in an attempt to promote germination. Low rates of H2O2 (0.5 M) and GA3 (1 g·L−1) were beneficial in some instances, whereas high rates of GA3 were detrimental. Nicking the seedcoats before stratification and soaking seeds in running water after stratification were ineffective in promoting germination. Germination temperatures of 32/22 °C (8 h/16 h) were superior to 22/22, 27/22, and 37/22 °C.
J.B. Magee, B.J. Smith, and Agnes Rimando
Control of muscadine diseases is necessary to minimize yield loss and is especially important for highest quality if the berries are to be marketed fresh. Throughout the 1998 growing season, vines of five muscadine cultivars (`Noble', `Summit', `Cowart', `Higgins', and `Carlos') were treated under a systematic disease control spray program; four fungicides registered for use on grapes were applied sequentially at 10- to 20-day intervals from early bloom until just before harvest. Control plants received no fungicide. The objectives of the study were to determine the effects of the spray schedule on foliage and berry diseases and to study the relationship between disease incidence and resveratrol content of the berries. Resveratrol is a phytoalexin and has been favorably implicated in cardiovascular disease and certain cancer processes. Foliar diseases were rated visually twice during the season. Berry disease ratings were made at harvest. All fungal foliage and berry diseases were significantly reduced by the fungicide treatments. Resveratrol concentrations were determined separately on berry skins, seed and pulp/juice by GC/MS. Overall, resveratrol levels in berry skins from unsprayed vines were much higher than those of sprayed vines. Concentrations varied by cultivar and within cultivar by treatment. The relationship of skin concentration and total disease score or scores of specific diseases has not been established. Seed resveratrol concentrations differed by cultivar but were not affected by the fungicide treatments. Mean concentration of seed was lower than that of skins. Accumulation of resveratrol in juice/pulp was much lower than in skins and seeds.
Hirofumi Terai, Alley E. Watada, Charles A. Murphy, and William P. Wergin
Structural changes in chloroplasts of broccoli (Brassica oleracea L., Italica group) florets during senescence were examined using light microscopy, scanning electron microscopy (SEM) with freeze-fracture technique, and transmission electron microscopy (TEM) to better understand the process of chloroplast degradation, particularly at the advanced stage of senescence. Light microscopy revealed that chloroplasts, which initially were intact and green, became obscure in shape, and their color faded during senescence. Small, colored particles appeared in cells as the florets approached the final stage of senescence and became full- to dark-yellow in color. Scanning electron microscopy showed that stroma thylakoids in the chloroplast initially were parallel to each other and grana thylakoids were tightly stacked. As senescence advanced, the grana thylakoids degenerated and formed globules. The globules became larger by aggregation as senescence progressed, and the large globules, called “thylakoid plexus,” formed numerous vesicles. The vesicles ultimately were expelled into the cytosol, and the light microscope revealed many colored particles in the senescent cells. These results indicate that the degradation of chloroplasts in broccoli florets progresses systematically, with the final product being colored particles, which are visible in yellow broccoli sepal cells.
James L. Glancey, Edwin Kee, and Tracy Wootten
The vegetable industry is important to our nation as a provider of nutritious and safe food directly consumed by our citizens. It is also critical to a rich and vigorous national agriculture. During the 20th century, engineering innovations coupled with advances in genetics, crop science, and plant protection have allowed the vegetable industry in the U.S. to plant and harvest significantly more land with higher yields while using less labor. Currently, fresh and processed vegetables generate 16% of all U.S. crop income, but from only 2% of the harvested cropland. Yet, many of the challenges in production that existed a century ago still exist for many crops. Perhaps the most significant challenge confronting the industry is labor, often accounting for 50% of all production costs. A case study of the mechanized production system developed for processed tomatoes (Lycopersicon esculentum) confirms that systematic methodology in which the machines, cultural practices, and cultivars are designed together must be adopted to improve the efficiency of current mechanized systems as well as provide profitable alternatives for crops currently hand-harvested. Only with this approach will horticultural crop production remain competitive and economically viable in the U.S.
S.S. Miller, R.W. McNew, B.H. Barritt, L. Berkett, S.K. Brown, J.A. Cline, J.M. Clements, W.P. Cowgill, R.M. Crassweller, M.E. Garcia, D.W. Greene, G.M. Greene, C.R. Hampson, I. Merwin, D.D. Miller, R.E. Moran, C.R. Rom, T.R. Roper, J.R. Schupp, and E. Stover
Cultivar and planting site are two factors that often receive minimal attention, but can have a significant impact on the quality of apple (Malus ×domestica) produced. A regional project, NE-183 The Multidisciplinary Evaluation of New Apple Cultivars, was initiated in 1995 to systematically evaluate 20 newer apple cultivars on Malling.9 (M.9) rootstock across 19 sites in North America. This paper describes the effect of cultivar and site on fruit quality and sensory attributes at a number of the planting sites for the 1998 through 2000 growing seasons. Fruit quality attributes measured included fruit weight, length: diameter ratio, soluble solids concentration (SSC), titratable acidity (TA), flesh firmness, red overcolor, and russet. Fruit sensory characteristics rated included crispness, sweetness, and juiciness, based on a unipolar intensity scale (where 1 = least and 5 = most), and acidity, flavor, attractiveness, and desirability based on a bipolar hedonic scale (where 1 = dislike and 5 = like extremely). All fruit quality and sensory variables measured were affected by cultivar. The two-way interaction of cultivar and planting site was significant for all response variables except SSC, TA, russet, crispness, and sweetness ratings. The SSC: TA ratio was strongly correlated with sweetness and acidity sensory rating, but was weakly correlated with flavor rating. The results demonstrate that no one cultivar is ideally suited for all planting sites and no planting site is ideal for maximizing the quality of all apple cultivars.
Xin Zhao, C.B. Rajashekar, Edward E. Carey, and Weiqun Wang
Demand for organically grown produce is increasing, largely due to concerns of consumers about health and nutrition. Previous studies have not shown a consistent difference of essential nutrients, such as vitamins and minerals, between organic food crops and the conventional counterparts. However, to date, little consideration has been given to phytochemicals, secondary plant metabolites with potential health-promoting properties. We first discuss factors that can infl uence the levels of phytochemicals in crops, and then we critically review the results of published studies that have compared the effects of organic and conventional production systems on phytochemical contents of fruit and vegetables. The evidence overall seems in favor of enhancement of phytochemical content in organically grown produce, but there has been little systematic study of the factors that may contribute to increased phytochemical content in organic crops. It remains to be seen whether consistent differences will be found, and the extent to which biotic and abiotic stresses, and other factors such as soil biology, contribute to those differences. Problems associated with most studies tend to weaken the validity of comparisons. Given the limitations of most published studies, needs for future research are discussed.