, half-high blueberry cultivars and southern highbush cultivars, are mixtures using these species. Half-highs have been produced by hybridization of 4 x V. corymbosum with 4 x V. angustifolium and retain a significant but variable percentage
Mark K. Ehlenfeldt, Joseph Kawash, and James Polashock
Chad E. Finn, James J. Luby, Carl J. Rosen, and Peter D. Ascher
Thirty-three seedling progenies from crosses among Vaccinium corymbosum L., V. angustifolium Ait., and V. corymbosum/V. angustifolium hybrid-derivative parents, and `Northblue', `Northsky', and `Northcountry' were grown for 2 years at three soil pH levels at Becker, Minn. Iron sulfate and lime were incorporated to amend the soil to pH levels of 4.0 and 6.5, respectively; the native soil, pH 4.5, was the third pH regime. The plants grew well in the low pH regime, poorly in the high pH regime, and intermediately in the native pH regime. Variation among populations was significant for all traits except vitality 18 months after being planted, and pH treatment affected all traits. The pH regime × population interactions were not significant for any of the plant performance characteristics. Nondestructive subjective and objective measurements were positively and highly correlated with total plant dry weight. Therefore, populations could be effectively evaluated for tolerance to higher pH without destroying the plant. Vaccinium angustifolium was not a general source of tolerance to higher pH, but some populations derived from V. angustifolium were tolerant of high soil pH.
Gregory A. Lang and E. James Parrie
Pollen from six southern highbush blueberry cultivars derived from Vaccinium corymbosum L. and one or more other species (V. darrowi Camp, V. ashei Reade, and V. angustifolium Aiton) was incubated on nutrient agar to determine tetrad viability, pollen tube growth rates, and incidence of multiple pollen tube germinations. `Avonblue' pollen had a significantly lower tetrad germination percentage than `Georgiagem', `Flordablue', `Sharpblue', `Gulfcoast', or `O'Neal', all of which had >90% viable tetrads. The in vitro growth rate of `O'Neal' pollen tubes was significantly higher than the growth rates of `Sharpblue' and `Georgiagem pollen tubes. Of those tetrads that were viable, more than two pollen tubes germinated from 83% and 91% of the `Gulfcoast' and `Sharpblue' tetrads, respectively, while only 11% of the `Flordablue' tetrads produced more than two pollen tubes. The total number of pollen tubes germinated per 100 tetrads ranged from 157 (`Flordablue') to 324 (`Sharpblue'), resulting in actual pollen grain viabilities ranging from 39% to 81%. Genetic differences in pollen vigor, as indicated by pollen viability, pollen tube growth rates, and multiple pollen tube germinations, may influence blueberry growers' success in optimizing the beneficial effects of cross-pollination on fruit development.
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.
E. James Parrie and Gregory A. Lang
Pollen deposition on the stigmatic surface of blueberry pistils was studied with regard to maximum pollen load and stigmatic fluid production (stigma receptivity). Three hybrid southern highbush cultivars (Vaccinium corymbosum L. with V. darrowi Camp, V. ashei Reade, and/or V. angustfolium Aiton), two northern highbush cultivars (V. corymbosum), and one hybrid half-high cultivar (V. corymbosum with V. angustifolium) were selfand cross-pollinated with counted pollen tetrads until saturation of the stigmatic surface occurred. Stigmatic saturation generally required 200 to 300 tetrads and was characterized by the cessation of stigmatic fluid production and the inability to absorb further tetrads. The loss of stigmatic receptivity was irreversible. Cross-pollination resulted in cessation of stigmatic fluid production at lower levels of tetrad deposition than did self-pollination, suggesting a potential pollen-stigma recognition phenomenon. Northern highbush, half-high, and southern highbush cultivars required 7% to 10%, 12% to 17%, and 14% to 21%, respectively, more self-pollen to develop the stigmatic saturation condition. The potential relation of the pollenstigma phenomenon to self-incompatibility mechanisms is discussed.
Daniel J. Bell, Lisa J. Rowland, James J. Polashock, and Frank A. Drummond
Latreille) ( Stubbs et al., 1996 ). In Maine, however, due to the recent decline of native pollinators, rented honeybees are generally stocked at approximately two to four hives per acre to achieve adequate pollination ( Drummond, 2002 ). V . angustifolium
Arlen D. Draper, Gene J. Galletta, Nicholi Vorsa, and Gojko Jelenkovic
Elden J. Stang, Malcolm N. Dana, Gavin G. Weis, and Brent H. McCown
K. Haghighi and J.F. Hancock
Restriction fragment analyses of chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA) were carried out on the principal cytoplasms of northern highbush cultivars and one representative of Vaccinium ashei Reade. Twenty-three restriction enzymes were used to identify variation and clarify mode of organelle inheritance. All species and genotypes displayed identical cpDNA fragment patterns, but high degrees of polymorphism were observed in the mitochondrial genomes. `Bluecrop' and `Jersey' did not appear to have `Rubel' cytoplasm as was previously believed. All hybrids contained maternal-type mtDNA.