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  • Author or Editor: H. J. Swartz x
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Abstract

Russet on ‘Golden Delicious’ apple (Malus domestica Borkh.) was induced by sprays of butanedioic acid mono-(2,2-dimethylhydrazide) (daminozide), Diazinon, superior oil, and by environmental factors. Russet severity was reduced by application of a silicon dioxide formulation and by protecting fruit from environmental conditions by bagging, plastic covers, or by filtering ambient air.

Open Access

Abstract

The cover is a color photograph of a painting of a ‘Tristar’ strawberry plant by Lynda Chandler at the end of the Beltsville 1980 fall harvest season. ‘Tristar’ and its sister cultivar, ‘Tribute’, are new strawberry introductions from the U. S. Department of Agriculture — University of Maryland breeding program (see also p. 792–795 for more details). These cultivars are the first to combine red stele and verticillium resistance from octoploid cultivated strawberry cultivars with a strong, cyclic expression of the everbearing character from a wild selection of octoploid Rocky Mountain strawberry. ‘Tribute’ and ‘Tristar’ are related through a common grandparent to the ‘Brighton’, ‘Hecker’, and ‘Aptos’ day-neutral cultivars recently introduced in California by Bringhurst and Voth.

Open Access

Abstract

Vigor, petiole length, stand, runner production, yield per square meter of matted row, and numbers of trusses per crown were greater in tissue culture-produced plants when compared to runner plants of strawberry (Fragaria × ananassa Duch). Leaf area and shape, number of serrations per leaflet, petiole pubescence density, flowers per truss, yield per crown, harvest time, small fruit weight, and percent imperfect fruits did not vary appreciably between propagation methods. Size of large fruit and mean fruit weight were less in tissue culture-produced plants. All changes in performance were caused, at least in part, by the increased vigor and axillary bud activity of tissue culture-produced plants. Tissue culture propagation of strawberry is particularly adapted to production of planting stock for nurseries because 60% more runner plants are produced from tissue culture plants. Production of variant plants from tissue culture was largely limited to 1 meristem-tip line. For certain cultivars, some adjustment of nursery inspection procedures for off-type plants will be required.

Open Access

Abstract

Comparative field performance of thornless blackberry plants produced by tissue-culture (TC) and standard (ST) methods (tip layers or stem cuttings) was studied to determine any effect of TC propagation on clonal phenotypic stability. In general, TC plants performed as well as, and were phenotypically similar to, ST plants. Some differences in leaf size and pattern were observed; however, the differences were related to the increased vigor of TC plants of these cultivars. Total growth of TC and ST plants of ‘Black Satin’, ‘Hull Thornless’, ‘Thornfree’, and SI-US 68-6-17 was similar. ST plants of ‘Dirksen Thornless’ and ‘Smoothstem’ failed to grow as rapidly as TC plants of these cultivars or ST plants of the other cultivars, resulting in significantly reduced 2nd-year yields. First-year growth of all TC plants was more uniform than corresponding ST plants. On the average, fruit size was smaller on TC plants; however, this was true in both years only for ‘Black Satin’. The response varied for other cultivars with TC plants of ‘Dirksen Thornless’ actually having larger fruits in one year. No consistent differences in bloom date or median harvest date due to propagation method were observed. No variant plants were observed in the field; however, one sectorial leaf chlorotic variant was observed after TC propagation but prior to field planting.

Open Access

A GUS marker was used in earlier experiments to show that crown gall resistant Vitis genotypes show significantly lower rates of transformation by A. vitis than the crown gall susceptible Vitis vinifera. In recent experiments a reporter gene (lacZ) fused with the virB promoter was used to determine whether the lower frequency of transformation resulted from reduced induction of Agrobacterium vitis virulence (vir) genes. With some A. vitis strains, addition of medium conditioned with grape tissue enhanced vir induction by the known inducer acetosyringone and significant vir induction also resulted without addition of acetosyringone when grape tissue was included in the induction medium. Enhancement of vir induction by grape extracts was not correlated with genotypic susceptibility to crown gall.

Free access

Abstract

Two methods of evaluating seedling drought resistance in Vaccinium (blueberry) spp. were examined. Twenty interspecific populations were greenhouse-grown and either matric-stressed in a dry 1 sand : 1 soil medium or osmotic-stressed in a nutrient solution containing polyethylene glycol (PEG). In both tests, population means were separated statistically by shoot damage ratings. The correlation (r = 0.46) between the two tests was positive and significant. Progenies of clones JU64 and JU62, which are sister seedlings (V. myrsinites Lamark × V. angustifolum Aiton), were the most drought-resistant. The soil screening test appeared more accurate because it grouped populations with common parentage. These tests indicated that the progenies differ in genetic capacity to resist drought.

Open Access

Progenies and clones of interspecific hybrid blueberries were evaluated for annual fraction of canopy volume (FCYV) and for difference in fraction of canopy volume between control and stressed plants [FCYV(C) - FCYV(S)] in a moderate water-deficit environment. The FCYV(C) - FCYV(S) data were used to determine combining ability effects. In addition, physiological processes of attached leaves of the clones were monitored with a portable photosynthesis apparatus. Specific combining ability (SCA) effects were significant for FCYV(C) - FCYV(S). The clone with the lowest mean for FCYV(C) - FCYV(S) was US75, a hybrid of Vaccinium darrowi Camp × V. corymbosum L. Clone JU64 (V. myrsinites Lamark × V. angustifolium Aiton) also had a low FCYV(C) - FCYV(S) mean, and its two progenies (JU64 × JU11 and G362 × JU64) had low progeny means. Stomatal conductance was lowered when blueberries were exposed to atmospheric and/or soil moisture stress that resulted in lower transpiration and photosynthesis and increased or equal water-use efficiencies (WUE). Blueberry plants adjusted to moisture stress as the season progressed by lowering stomatal conductance and increasing WUE. In particular, stressed plants of US75 and JU64 had equal or higher WUE values than control plants. US226 was the most drought-susceptible clone in the study, and its stomata did not appear to be as responsive to moisture stress as the other clones. Breeding for higher WUE in a dry environment appears possible with the germplasm used in this study.

Free access

Interspecific blueberry (Vaccinium spp.) progenies were examined to determine combining abilities and genetic variability for seedling root system size and shoot vigor and to establish whether a large root system is correlated with good growth when plants are grown on a mineral soil and exposed to a moderate soil water deficit. General combining ability (GCA) variance components for root system size and shoot vigor and specific combining ability variance components for shoot vigor were significant. US226, a tetraploid hybrid of V. myrtilloides Michaux × V. atrococcum Heller, had the highest GCA effect for root system size and the lowest GCA effect for shoot vigor. US75 (V. darrowi Camp × V. corymbosum L.) had the highest GCA effect for shoot vigor and was second in GCA effect for root system size. Comparison of the crosses containing G111 (V. corymbosum) with those containing G362 (V. corymbosum) indicates that selecting for the best V. corymbosum clone to start a breeding program seems as important as selecting the mineral soil-adapted parent. Root system ratings were highly correlated with total dry weight of field-grown plants (r = 0.89). The method used in this study to evaluate seedlings for root system size and shoot vigor could be used to eliminate the less vigorous plants from a population before field planting and to evaluate mineral soil adaptability.

Free access

The relationship between moisture stress and mineral soil tolerance was studied by placing 10 blueberry (Vaccinium) clones in a Berryland sand soil high in organic matter (Berryland) and a Galestown sandy clay loam soil (Galestown) and subjecting them to one of two moisture regimes. The Berryland and Galestown soils represent an excellent blueberry soil and a mineral soil, respectively. A moderate degree of water stress influenced biomass partitioning in blueberries in a similar manner as stress induced by culture on mineral soil. Berryland control plants on Berryland partitioned more biomass into leaves and produced more dry matter and leaf area than plants on Galestown or those moisture stressed. Net assimilation rate and relative growth rate were not significantly different between soil or moisture treatments. The primary reason for the reduction in absolute growth rate due to soil type or moisture stress was a significantly lower leaf area duration on Galestown soil and in-moisture stressed plants. Clones differed in instantaneous transpiration, leaf conductance, and apparent photosynthesis and the ability to partition biomass into various plant parts. By selecting for increased leafiness, a high photosynthetic rate, and a more energy efficient root system, improvement in mineral soil tolerance should be possible.

Free access

Regeneration of adventitious shoots from in vitro-derived leaves of several Rubus genotypes was tested with various concentrations of cytokinins and auxins, different basal media, duration of dark incubation periods, temperatures and photosynthetic photon fluxes (PPF). Thidiazuron (TDZ) was significantly more effective than benzyladenine (BA), and indolebutyric acid (IBA) more effective than naphthaleneacetic acid (NAA). Leaves of `Summit' and `Sentry' raspberries and MD-ETCE-1 blackberry were most responsive (percentage of leaves responding, number of shoots formed) to 1 μM or 10 μM TDZ plus 0.5 μM or 1 μM IBA; MD-ETCE-1 leaves did not respond to BA or TDZ with either 2.7 or 5.4 μM NAA. More organogenesis occurred on MS than on half-strength MS, Anderson modified, WPM or N6 media. For the five cultivars tested (`Autumn Bliss', `Canby', `Sentry', `Summit', MD-ETCE-1), the most shoots formed when leaves were incubated at 20°C (vs. 25°C) for 1 week in the dark before they were exposed for 16 h per day to a PPF of 40 μmol·m-2·s-1. Significant differences in regeneration frequency were observed among four cultivars with the highest 71% for `Autumn Bliss' and the lowest 29% for `Summit'.

Free access