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- Author or Editor: M. Stevens x
Collection and estimation of root material are likely some of the greatest challenges of whole-plant sampling. As with other perennial crops, season of sample collection is also a challenge in grape whole-plant sampling. Our interest is in collecting grape whole-plant samples from an established (>25-year-old) vineyard to study plant nutrient partitioning. Before launching into routine sampling, two techniques were compared for very fine, fine, and coarse root distribution. For very fine and fine root sampling, soil cores were collected in a radial pattern around the vine trunk at eight sample points, each either 20, 60, 120 cm from the trunk or 50, 100, and 150 cm from the trunk. Roots were washed from the soil material, separated into fractions and weighed. For evaluation of techniques for sampling fine and coarse roots, roots were either excavated by tracing them from the trunk in about a 1-m3 soil volume or by extracting about the same soil volume using a backhoe and shaking the soil free of the roots. Overall, the more narrow soil core sampling gave a greater total root mass and both the tracing and backhoe methods gave similar results. In addition, pruning weight measurement is also frequently measured in grape research. We compared using the NDVI (Normalized Difference Vegetation Index) device, the “Greenseeker”™, with pruning mass to determine if this device could be used as a non-destructive measurement for grape pruning weight.
Past experiments have proven that meristem tip-cultured blueberry plantlets are extremely difficult to inoculate using laboratory-grown cultures of existing known isolates of Hymenoscyphus ericae, Scytalidium vaccinii, and Oidiodendron griseum; fungi that have been previously established as ericoid mycorrhizal symbionts. An experiment using both seedling and meristem tip-cultured plantlets was conducted using these proven fungal symbionts from the Canadian Fungal Culture Collection (DAOM), as well as fungi isolated from local blueberry populations at Little Flat, Pa. Treatments included inoculation using soil from the Little Flat population, the same soil (autoclaved), autoclaved soil that was reinoculated with fungi, as well as axenic treatments using H. ericae, S. vaccinii, O. griseum, Little Flat Hymenoscyphus sp., Little Flat Scytalidium sp., and Little Flat Oidiodendron sp. Sampling after 21 days revealed that only the nontreated soil plantlets were infected (≈4%). Results from later sampling dates will be presented, and the mechanism of infection discussed.
The ability to monitor plant nutrient status of high value horticultural crops and to adjust seasonal nutrient supply via fertilizer application has economic and environmental benefits. Recent technological advances may enable growers and field consultants to conduct this type of monitoring nondestructively in the future. Using the perennial crop apple (Malus domestica) and the annual crop potato (Solanum tuberosum), a hand-held leaf reflectance meter was used to evaluate leaf nitrogen (N) status throughout the growing season. In potato, this meter showed good correlation with leaf blade N content. Both time of day and time of season influenced leaf meter measurement, but leaf position did not. In apple, three different leaf meters were compared: the leaf spectral reflectance meter and two leaf greenness meters. Correlation with both N rate and leaf N content were strongest for the leaf reflectance meter early in the season but nonsignificant late in the season, whereas the leaf greenness meters gave weak but significant correlations throughout the growing season. The tapering off of leaf reflectance values found with the hand-held meter is consistent with normalized difference vegetation index (NDVI) values calculated from satellite images from the same plots. Overall, the use of leaf spectral reflectance shows promise as a tool for nondestructive monitoring of plant leaf status and would enable multiple georeferenced measurements throughout a field for differential N management.
Abstract
Sensory evaluations and chemical analyses were used to investigate the effects of various postharvest handling procedures on composition and flavor quality of ‘Cal Ace’ tomatoes (Lycopersicon esculentum Mill.) harvested at the mature-green and light-pink stages. Ethylene treatment to speed ripening of green tomatoes at 20°C resulted in a higher reduced ascorbic acid content at the table-ripe stage and did not influence flavor when compared with fruits ripened without added ethylene. Using a low-O2 atmosphere to retard ripening had less of an effect on flavor than stage of ripeness at harvest. No differences were found between fruits where ripening was delayed by using 4% O2-atmosphere at 20° or by using low temperature (12.5°). Exposing fruits to 5° for 7 days before ripening at 20° affected flavor; i.e., chilled fruits were more acid. Above the chilling range (0-12.5°); duration of holding after harvest was more important than storage temperature. Lower holding periods resulted in loss of characteristic “tomato-like” flavor and development of “off-flavors.” Mature-green fruits, ripened at 20° under restricted air flow, had increased “off-flavors” when compared to those ripened under accelerated air exchange. Light-pink fruits subjected to impact bruising before ripening had more “off-flavor” and less “tomatolike” flavor than those without physical damage. Quantitative differences in a few volatile components were found with certain treatments, but no qualitative differences were detected and there was no significant difference in total volatile content among any of the treatments tested.
Abstract
Four amino acids (glutamic, γ-aminobutyric, glutamine, and aspartic) make up about 80% of the total free amino acids in fruits of tomato (Lycopersicon esculentum Mill., cv. Cal Ace). Fruits harvested at the table-ripe stage contained more alanine and less glutamic acid than those picked green or at the breaker (incipient red color) stage and ripened at 20°C to table-ripe. The higher glutamic acid concentrations in fruit picked at the breaker or earlier stages were paralled to higher scores for “off-flavor,” as described by a taste panel, relative to fruits picked table-ripe. However, when monopotassium glutamate (60, 120, or 180 mg/l00g) was added to diced table-ripe fruits, the panelists were not able to detect flavor differences due to increased glutamic acid concn. Differences in amino acid composition associated with fruit ripeness when picked do not appear to be directly related to flavor differences.
Abstract
Composition and sensory characteristics were investigated to determine the effect of ripeness at picking on fresh market flavor of ‘Cal Ace’ (1974, 1975, 1976) and ‘Cherry’, ‘Calmart’, and ‘Early Pak 7’ (1976) tomato (Lycopersicon esculentum Mill.). Tomatoes picked at earlier stages of ripeness and ripened at 20°C were evaluated by panelists as being less sweet, more sour, less “tomato-like” and having more “off-flavor” than those picked at the table-ripe stage. Objective tests showed these fruits had less sugars and reduced ascorbic acid, and varied significantly in volatile composition. The magnitude of these differences varied greatly among the cultivars. In ‘Cal Ace’ the “off-flavor” characteristic was largely correlated with a volatile compound (peak 43) but in other cultivars seven other volatile compounds also appeared to play a role.
A three year study involving solar heating of soil (soil solarization) with clear polyethylene mulch demonstrated for two years, control of root-knot nematodes (Meloidogyne incognita). The population of M. incognita was reduced >90% in the 0-30cm depth of solarized soil. The number of eggs per gram root recovered and the root gall index from `Georgia-Jet' sweetpotatoes were reduced (92-98%) by soil solarization. Growth and yield were enhanced in solarized soil. The beneficial effects of solarization was observed in the second year following two additional cropping cycles of collard greens and sweetpotatoes.
Field plots on Norfolk sandy loam soil at Tuskegee and Eufaula, AL were treated by soil solarization (SS). Samples rhizsosphere (R) and nonrhizosphere soil from cole crop and strawberry plots were collected and assayed with selective media for population densities of microbes involved in organic decomposition and mineralization. Microflora population densities of bacteria, actinomycetes and fungi increased 2-7 folds in the solarized compared to the bare soil (BS). Microflora population densities in the soils involved in cellulose and protein decomposition, ammonification, nitrification, phosphate mineralization were greater in solarized soil compared to BS. Nitrogen-fixing bacteria in R soil 7 months after SS was higher when compared to BS at Tuskegee, but was reduced 50 folds 18 months after SS.
Understanding water and nutrient movement in arid climate-regulated deficit, drip-irrigated vineyards is imperative for understanding grape vine canopy management. However, little research has been conducted in these environments to aid in the understanding of where the vine accesses nutrients and/or soil water and how that translates into soil and/or plant tissue sampling approaches. We used bromide (Br) as a tracer to study nitrate movement in soils as well as into grape leaves in two ‘Merlot’ vineyards in central Washington State. Bromide movement closely followed water movement. Although Br was detectable in grape petioles, it was not detectable in leaf blades, likely as a result of a dilution factor related to the amount of tissue. Relationships between soil Br and soil moisture as well as petiole and soil Br concentrations suggests that soil sampling for nitrate should be taken from a diagonal position between the vine and the emitter, between 20 and 60 cm from the drip line. This is consistent with the recommendation for soil moisture sampling in a published companion study.
In 1988 and 1989 a muscadine vineyard at Tuskegee, Alabama was treated by post soil solarization (PSS) (covering of moist soil around muscadine plants with clear polyethylene plastic mulch to achieve high soil temperature) for 30 and 75 days, respectively. The average soil temperature in 1989 of 50 and 35 C at 5cm depth for solarized and bare soil, respectively during PSS. The results showed no visible detrimental effect on `Carlos' muscadine (Vitis rotundifolia) from the increased heating of the soil. And the grape plants grown in solarized soils showed increases in growth response e.g. increased yield, revitalization of new softwood vines, vine weight/plant, etc. Uneven ripening of muscadine grapes was reduced on plants grown in PSS over bare soil as indicated by the increases in the percent soluble solids content of grape berries.