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Luping Qu and J.F. Hancock

RAPD markers were used to determine the level of heterozygosity transmitted via 2n gametes from V. darrowi cv. Florida 4b (Fla 4B) to interspecific hybrids with tetraploid V. corymbosum cv. Bluecrop. The tetraploid hybrid US 75 was found to contain 70.6% of Fla 4B's heterozygosity, a value consistent with a first division restitution (FDR) mode of 2n gamete production. Crossovers during 2n gamete formation were evidenced by the absence of 16 dominant alleles of Fla 4B in US 75, and direct tests of segregation in a diploid population involving Fla 4B. RAPD markers that were present in both Fla 4B and US 75 were used to determine the mode of inheritance in a segregating population of US 75 × V. corymbosum cv. Bluetta. More than 30 homozygous pairs of alleles were located that segregated in a 5:1 ratio, indicating US 75 undergoes tetrasomic inheritance.

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S. Serce and J.F. Hancock

A common complaint with day-neutral strawberries is that they perform poorly in mid-summer heat. Since most modern day-neutral cultivars are derived from the same Fragaria virginiana ssp. glauca clone from Utah, we felt it prudent to search for alternate sources of day-neutrality that were more heat-tolerant. We compared the sexual and vegetative performance of nine F. virginiana clones from a wide range of environments including the Utah site, and four F. × ananassa day-neutral types (`Aromas', `Fort Laramie', `Ogallala', and `Tribute') under constant temperatures of 18, 22, 26, and 30 °C and 12-h days. `Aromas' and `Tribute' carry the Utah source of day-neutrality, while `Fort Laramie' and `Ogallala' are old cultivars that have a different, complex background. After a 4-week period of acclimation, we counted the number of crowns, inflorescences, flowers, stolons, and daughter plants that emerged over a 10-week period, and measured the dry weights of component parts. ANOVA tables revealed that temperature regime (T), genotypes (G), and T*G were significant for flower number (FLN) and total dry matter accumulation, while species and T*G were significant for daughter plant number (DPN). Mean FLNs across the four temperatures were 6.8, 3.7, 3.3, and 1.2, while mean DPNs were 0.7, 0.9, 0.7, and 1.8. F. virginiana clones averaged 3.8 FLNs and 1.8 DPNs, while the F. × ananassa clones averaged 4.1 FLNs and 0.2 DPNs. There was generally more variability among the F. virginiana clones than the F. × ananassa clones, but the F. × ananassa cultivars, `Fort Laramie' and `Ogallala', performed best at 30 °C. The Wasatch clone did not flower in any treatment, suggesting it is not day-neutral.

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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.

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J.D. Carlson and J.F. Hancock Jr.

Fifteen years of Michigan harvest data for highbush blueberry (Vacciniun corymbosum L.) were used in conjunction with daily maximum and minimum temperatures to determine appropriate heat-unit models for first-picking dates of 13 cultivars. For each cultivar, an optimal heat-unit model was chosen after evaluating the performance of a standard method with 72 combinations of three variables: a) starting date for the heat-unit accumulations (SDATE), b) low-temperature threshold (TLOW), and c) high-temperature threshold (THIGH). The optimal model sought to include the most important criteria values with respect to model performance and to minimize the average square of the prediction error (days) and the range in that error. Compared with a strict calendar-day method of estimating harvest dates, the heat-unit models reduced the standard deviation of the prediction error from 22% to 69%, depending on cultivar.

Open access

J. A. Siefker and J. F. Hancock

Abstract

The effect of pruning was evaluated by removing varying amounts of different-sized canes from 15-year-old highbush blueberry plants. As much as 40% of a bush could be removed before yield was reduced. There was a significant correlation (P < 0.05) between percent base area removed and berry weight, suggesting a compensation for reduced basal area by increasing berry weight. The number of new canes also was significantly correlated with the number removed. The size of canes removed was less important than the percent basal area removed, except in the most extreme treatment (40% removed), where the removal of medium-sized (1-2.5 cm) canes had a greater effect than the elimination of large canes.

Open access

J.H. Siefker and J.F. Hancock

Abstract

Yield component analysis of 9 Vaccinium corymbosum L. blueberry cultivars indicated that yield was more strongly determined by canes per bush and berries per cane than by berry weight. High numbers of berries per cane were associated with low berry weights in all cultivars. Component interactions ranged from slightly additive in ‘Bluecrop’ and ‘Spartan’ to highly compensatory in ‘Rubel’ and ‘Berkeley’. The consideration of component interactions in cultivar trials may enhance the accuracy in identification of desirable genotypes.

Open access

J. Scott Cameron and James F. Hancock

Abstract

Micropropagated mother plants of strawberry (Fragaria × ananassa Duchesne) often produce more flowers and runners than their runner-propagated counterparts (4, 5), but it is not clear how long this effect lasts. Swartz et al. (5) reported that the increase in runnering of tissue culture plants did not continue after the first flush of runner production in the field, and Marcotrigiano et al. (4) showed that, within the planting year, micropropagation increased runner production in mother plants and their primary runner plants, but not in attached secondary and tertiary runner plants. However, these studies examined runner plants still attached to plants directly out of culture, rather than detached, cold-hardened plants as they are delivered to the grower. In a study where detached runner plants of unknown age were compared, planting stock from micropropagated plants of 4 of 6 cultivars had significantly higher matted row densities ( X ¯ = 63%) than those derived from conventionally propagated stock (2). The goal of this study was to compare the performance of detached primary, secondary, and tertiary runner plants of micropropagated (MP) and standard (ST) mother plants grown under controlled conditions.

Open access

A. R. Putnam and J. F. Hancock

Abstract

Preplant-incorporated and post-transplant applications of napropamide [2-(α-naphthoxyl)-N, N-diethylpropionamide] were compared with 2 standard preemergent herbicides for safety on newly transplanted ‘Midway’ stawberries (Fragaria X ananassa Duch). Napropamide at rates up to 4.4 kg/ha caused no reduction in stolon or daughter plant production, or in rooting of daughter plants in the first season of growth. There was no adverse effect on fruit yield the following season when compared to hand-weeded controls. The plants responded similarly to the 2 application methods, except that slightly higher yields were obtained when all herbicides were preplant-incorporated.