Search Results

You are looking at 41 - 50 of 51 items for

  • Author or Editor: J. A. Flore x
Clear All Modify Search

`Imperial Gala' apple trees on M.9 EMLA, MM.lll and Mark rootstocks were subjected to two drought and recovery periods in a rainshelter. The objectives were to determine rootstocks adaptation and parameter sensitivity to drought stress. Leaf growth rate, area, emergence; shoot length, trunk cross sectional area and gas exchange were measured for each stress and recovery period. Leaf growth rate was most consistently reduced by drought and returned to control levels when irrigated. Length of less vigorous shoots was consistently reduced by stress but did not recover upon irrigation. Leaf emergence and trunk cross sectional area were inconsistent in response to stress. Growth of trees on Mark rootstock was reduced to the greatest extent by drought followed by MM.lll and M.9 EMLA. At termination plants were separated into roots, 1-year and 2-year shoot growth and rootstock to determine dry weights. Dry weights confirmed the growth measurements with a 34%, 27% and 16% reduction in total plant dry weight for drought stressed trees on Mark, MM.lll and M.9 EMLA, respectively. The greatest differences in estimated whole plant photosynthesis were for trees on Mark rootstock followed by MM.lll with the least differences for M.9 EMLA which reinforced the growth measurements. It was concluded that Mark was most sensitive followed by MM.lll with M.9 EMLA being most tolerant to drought.

Free access

Seven highbush blueberry (Vaccinium corymbosum L.) cultivars were evaluated for their photosynthetic heat stability. Ail showed significant reductions in CO2 assimilation rates (A) as leaf temperatures were raised from 20 to 30C, although `Blue-crop', `Jersey', `Elliot', and `Rubel' (22% to - 27%) were significantly less affected than Spartan', `Bluejay', and `Patriot' (-41% to -51%). To determine whether temperature adaptations of highbush types can be broadened through hybridization with native, heat-tolerant species, `Bluecrop' was crossed with the V. darrowi Camp. selection Florida 4B, and F2, BC1, and BC2, populations were generated. This approach showed promise as genotypes were identified in all the derivative populations that were more heat tolerant than `Bluecrop' and had a high A.

Free access

Both berries and roots of grapevines are powerful carbohydrate sinks. However, during periods of soil-moisture stress, the relative strength of these two sinks is not known. This experiment was conducted to evaluate interrelationships between differing crop loads on carbohydrate partitioning for above and below-ground tissues. Root development, depth, and rate of turnover were determined by quantifying root images from video recordings taken to depths of 75 cm at two week intervals throughout the growing season. Two-year old own rooted Seyval grapevines, and Seyval grafted to 5-BB and Seyval, were grown under a rain exclusion shelter and provided with 10 or 2.5 liters of water/plant/week. Treatments were cropping level, either 0 or 6-clusters/vine. Shoot length, number of mature nodes, and dry leaf weight of vines under high cropping level were significantly reduced compared to vines growing under the low cropping level; so was root number and depth of root penetration. These data suggest that conditions of low soil moisture result in carbohydrate partitioning in favor of the clusters at the expense of the roots.

Free access

Abstract

(2-Chloroethyl)phosphonic acid (ethephon) applied as a foliar spray to sweet cherry trees within 2 weeks of fruit maturity promoted fruit abscission at the lower (fruit:pedicel) zone, as indexed by a reduction in the fruit removal force (FRF). There was no significant effect, at the concn studied, on abscission at the upper (pedicel:peduncle) zone. Promotion of abscission with ethephon was time and concn dependent. Ethephon concn of 100 to 1000 ppm were effective with a greater response from the higher concn. Absorption periods of 4 and 24 hr resulted in responses equal to 73 and 94% of that observed when ethephon was present for the entire experimental period. Of 9 sweet cherry cultivars evaluated, all responded similarly in terms of reduction in FRF. Ethephon enhanced fruit enlargement and pigmentation when applied early in Stage III of fruit growth. The increase in wt was most pronounced in the fleshy pericarp tissue.

Open Access

Abstract

Second-order rectangular hyperbolic and asymptotic models which predict spur and terminal leaf expansion of ‘Montmorency’ sour cherry (Prunus cerasus L.) were developed from leaf area observations and temperature records made in orchards near East Lansing, Mich. Average leaf area per leaf was more highly correlated with degree-day accumulation at a base of 4°C starting April 19, than with day of the year. Leaf area per leaf increased linearly with degree-day accumulation until full leaf expansion. Final spur or terminal leaf size was not constant between years.

Open Access

Three systems of peach production have been established (Flore, et al., 1991, HortScience 26(6):747) utilizing three levels of chemical input: conventional input, moderate level, and low level. The moderate and low levels of chemical input use increasing degrees of IPM. In 1992, data were collected on yield, insect and disease impact on fruit quality, vegetative growth, nitrate and simazine levels in the soil, and insecticide residues in the fruit. The yield per tree was substantially higher in the conventional treatment but this effect could be attributed to an early spring frost, local topography, or the treatment system. The percentage of fruit free from insect and disease damage was highest in the conventional treatment (95.1%), but the low input had a relatively high percentage of fruit free of damage (79.6%). Shoot cold hardiness of one year old shoots was not affected by treatment. Bud survival after a spring frost was greater in the conventional orchards, but topography may have influenced this parameter. Nitrate levels 2 m in the soil and sim-azine residues in the A horizon were not affected by treatment. Lorsban®, Guthion®, and Asana® residues in fruit are currently being analyzed and will be discussed. Additional data collected in 1993 and future years will contribute more information on the use of the low and moderate chemical input treatments on peach production.

Free access

`Jonnee' on M.9 EMLA, M.26 EMLA and Mark rootstocks were subjected to flooding for 2, 4, 8, 16 and 32 days duration. Recovery was monitored after each stress period until 28 days after the 32 day flood stress. The objectives were to determine growth and physiological adaptation of the three rootstocks to flooding. Gas exchange, root dynamics, leaf area and emergence, and shoot length were measured for each stress and recovery period. CO2 assimilation initially was increased for flooded treatments of Mark and M.9 EMLA up to 300% and 200% of controls until three days after flooding. After 4 days of flooding, CO2 assimilation decreased to 30% or less of controls for both rootstocks. No initial increase was seen for flooded M.26 EMLA, rather a steady decline until net respiration occurred. Root number was not affected until 32 days of flooding where all flooded treatments had fewer roots counted compared to controls. After release from flooding trees on Mark recovered root growth while M.9 EMLA and M.26 EMLA continued to decline in root numbers. Shoot system growth of flooded trees on M.26 EMLA was reduced first and to the greatest extent followed by Mark and then M.9 EMLA.

Free access

Abstract

A 2nd order equation relating net photosynthesis (Pn) to photosynthetic photon flux density (PPFD), temperature, and CO2 was determined from single leaf CO2 depletion measurements made with an open gas analysis system. From this information, a photosynthetic optimization equation was used as the basis for computer regulation of greenhouse environment control using 2 strategies. In strategy 1, both temperature and CO2 setpoints were reset every 15 min based on the PPFD in the greenhouse. In strategy 2, only the temperature setpoint was reset, CO2 was ambient. The calculated setpoints represented temperature and/or CO2 values, where predicted Pn was maximized at the particular PPFD. Both strategies were compared to a typical commercial chrysanthemum environment of 16/20/24°C (night/day/vent) with ambient CO2. Chrysanthemum morifolium Ramat. (‘Bright Golden Anne’) grown in the temperature and CO2 optimized environment had significantly greater leaf, stem, and total dry weight at flowering compared to the other 2 environmental strategies. The percentage of stem dry weight and the stem length also were increased. For all 3 planting dates the percentage of flower dry weight was reduced but statistically significant on 1 date only. Flowering date was not affected. No consistent statistical differences in plant development were observed between the temperature optimized environment and the traditional environment.

Open Access

When sweetpotato chlorotic stunt crinivirus (SPCSV) and sweetpotato feathery mottle potyvirus (SPFMV) infect sweetpotato [Ipomoea batatas (L.) Lam.], they interact synergistically and cause sweetpotato virus disease (SPVD), a major constraint to food productivity in east Africa. The genetic basis of resistance to these diseases was investigated in 15 sweetpotato diallel families (1352 genotypes) in Uganda, and in two families of the same diallel at the International Potato Center (CIP), Lima, Peru. Graft inoculation with SPCSV and SPFMV resulted in severe SPVD symptoms in all the families in Uganda. The distribution of SPVD scores was skewed toward highly susceptible categories (SPVD scores 4 and 5), eliminating almost all the resistant genotypes (scores 1 and 2). Likewise, when two promising diallel families (`Tanzania' × `Bikilamaliya' and `Tanzania' × `Wagabolige') were graft inoculated with SPCSV and SPFMV at CIP, severe SPVD was observed in most of the progenies. Individual inoculation of these two families with SPCSV or SPFMV, and Mendelian segregation analysis for resistant vs. susceptible categories led us to hypothesize that resistance to SPCSV and SPFMV was conditioned by two separate recessive genes inherited in a hexasomic or tetradisomic manner. Subsequent molecular marker studies yielded two genetic markers associated with resistance to SPCSV and SPFMV. The AFLP and RAPD markers linked to SPCSV and SPFMV resistance explained 70% and 72% of the variation in resistance, respectively. We propose naming these genes as spcsv1 and spfmv1. Our results also suggest that, in the presence of both of these viruses, additional genes mediate oligogenic or multigenic horizontal (quantitative) effects in the progenies studied for resistance to SPVD.

Free access

Twenty-one western and 13 eastern strawberry [Fragaria × ananassa (Duch.)] cultivars were grown in a polyethylene-covered greenhouse (polyhouse) in deep beds at either 10 × 10 or 25 × 25 cm spacing. Runners were removed weekly from the closest-spaced plants (hills), and the more open-spaced plants were allowed to set four runners on each side of the mother plant before the runners were removed (matted rows). Temperatures were allowed to fluctuate normally in the polyhouse, except that winter temperatures were maintained above 0C. The average yield of eastern and western cultivars did not differ significantly in most comparisons, but the average fruit weight of the Californian cultivars was significantly higher than the eastern ones, and Californian cultivars allocated a higher proportion of their biomass to reproduction. Nonbearing plants of eastern and western cultivars produced similar numbers of runners per plant and daughters per runner. There was no significant relationship between CO2 assimilation rate and yield. Interbreeding eastern cultivars with the most productive western genotypes might result in increased yields, but only if the higher reproductive efforts of the western types can be captured and transferred.

Free access