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W.A. Erb, A.D. Draper and H. J. Swartz

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.

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W.A. Erb, A.D. Draper and H.J. Swartz

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.

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W.A. Erb, A.D. Draper and H.J. Swartz

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.

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Doru Pamfil, R.H. Zimmerman, S.K. Naess and H.J. Swartz

RAPD analysis was performed on 44 species of Rubus. These species included representatives from seven of the 12 subgenera within the genus and several series within the Idaeobatus (raspberries) and Eubatus (blackberries) subgenera. For all species, up to five plants were initially analyzed by two 10-mer primers. The most heterozygous of these individuals was then analyzed using 13 additional primers. Wide band diversity exists among Rubus species; these differences were analyzed using the PHYLIP software program. These differences are repeatable, for example color sports of `Heritage' red raspberry produced identical banding patterns. The genetic similarity between eastern United States blackberries (Eubatus) and numerous species was compared to the ability of these same species to act as a suitable pollen parent for eastern blackberries. These data were used to construct a dendrogram of the subgenera studied here.

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W.A. Erb, A.D. Draper, G.J. Galletta and H.J. Swartz

Data from a four-parent diallel, involving one highbush (Vaccinium corymbosum L.) clone and three interspecific hybrids grown on mineral soil unamended with organic matter, were analyzed to determine combining ability effects for six traits: plant size, berry size, the number of days between flowering and fruiting (# DBF&F), the ratio of total fruit weight to canopy volume (TFW: CYV), days to fruit ripe, and yield. General combining ability effects were significant for all characters tested, except yield and berry size in 1984. Specific combining ability effects were significant for plant size in 1983, #DBF&F in 1984, TFW: CYV in 1984, and berry size in 1985. Vigorous and productive highbush cultivars can be developed for mineral soils by using the interspecific clones from this study and their selected recombinant to combine the genes for plant vigor with the high-quality fruit traits of highbush cultivars.

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J. Cummaragunta, D.V. Schlimme, C.S. Walsh, H.J. Swartz and A.E. Watada

In 1993, we studied the postharvest behavior of 25 Rubus genotypes. Included in the study were named cultivars from Europe and North America, advanced selections from the Univ. of Maryland Cooperative Breeding Program, species and raspberry interspecific hybrids, with R. phenicolasius, R. pungens oldhamii R sumatranus, and R parvifolius. Wide variation exists in the ethylene production rates of these genotypes. The difference between the lowest ethylene producer, R. phenicolasius, and the highest ethylene evolver, HTCC-6t (R. lasiostylus), was four orders of magnitude. Ethylene evolution rate and percentage mold were not correlated. Ethylene production and respiration rates were also measured using a flowthrough system. No single pattern was characteristic of all genotypes. Red raspberries were the highest ethylene producers and showed an ethylene and respiratory climacteric. Blackberries were low ethylene producers. Interspecific hybrids showed varied postharvest behaviors. The behavior observed in these interspecific hybrids may explain some of the conflicting reports on the postharvest behavior of blackberries and raspberries. In general heattolerant species such as blackberry, R. occidentalis, R. parvifolius exhibited lower rates of respiration and ethylene evolution than species from cool, temperate areas like R. idaeus.

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G.J. Galletta, J.L. Maas, J.M. Enns, A.D. Draper, A. Dale and H.J. Swartz