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Paul E. Cappiello and Scott Dunham

Commercial lowbush blueberry production involves management of what have long been considered highly diverse populations of naturally occurring clones. Wide phenotypic variation evident in fields has often been anecdotally equated with variation in yield, cultural requirements, etc., however this has not been tested rigorously. Interest in selection of clones with superior low-temperature tolerance prompted this study to estimate population-wide variation within the species. Thirty six clones of Vacciniun angustifolium exhibiting most of the typical phenotypic classes were selected from two commercial production fields in Maine. Plants were evaluated for low-temperature tolerance of reproductive and vascular tissues on a monthly basis from November through April. In addition, variation in relative time of anthesis, flower structure, and floral low-temperature tolerance were determined. Results are discussed with respect to potential for selection of superior clones for both fruit production and ornamental use.

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John M. Smagula and Scott Dunham

A commercial lowbush blueberry (Vaccinium angustifolium Ait.) field deficient in leaf N and P was used to compare organic and inorganic fertilizers. In a RCB design with eight replications of 12 treatments, experimental plots received 33.6 or 67.2 kg·ha-1 rates of N (urea), P (23% phosphoric acid), N + P (DAP), N + P + K (5-10-5), or N + P + K (fish hydrolysate, 242). Fertilizer containing N alone was as effective in raising N leaf concentrations as those containing N and P. However, leaf P concentrations were raised more by fertilizer providing N and P than only P. Fish hydrolysate fertilizer was as effective as 5-10-5 in raising leaf N, P, and K concentrations in prune and crop year leaf samples. At the 67.2 kg·ha-1 rate, fish hydrolysate, N, NP and NPK increased stem length, N and NP increased flower bud density and fish hydrolysate, N and NPK increased yield compared to the control.

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John M. Smagula and Scott Dunham

Eight commercial lowbush blueberry fields received preemergent application of diammonium phosphate at 0, 44.8, or 89.6 kg P/ha. Leaf samples taken in July of the application year showed a linear increase in P concentration with increasing DAP application. However, P concentrations in soil samples were not raised by DAP. Stem length, branching, and the number of flower buds per stem increased with DAP application. Yield, obtained by hand raking the 3 × 9-m treatment plots, increased with increasing rate of DAP. The average yield increase in response to 44.8 and 89.6 kg P/ha from DAP was 824 and 1679 kg/ha, respectively.

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John M. Smagula and Scott Dunham

Flail mowing was compared to traditional pruning by oil fire over a 12-year period in two fertility experiments testing interactions with pruning method. In study one (1983–1986), urea at 0, 22.4, 44.8, 67.2, or 89.6 kg·ha–1 was applied preemergent in a split-block design with fertility as the main effect, and pruning method split within six blocks. Study two (1987–1994) continued the pruning and application of fertilizer on the treatment plots with similar rates, but diammonium phosphate (DAP) replaced urea as the fertilizer. Leaf tissue N concentrations were above the 1.6% standard and urea had no effect or decreased yield. There was no interaction of fertility and pruning and no effect of pruning method on yield. No interaction of fertility and pruning was found in study two, but DAP increased leaf P concentrations and yield and, after three cycles of mowing, yields had begun to decline in mowed plots compared to burned plots. No meaningful differences in leaf nutrient concentrations were found between plants in mowed and burned plots.

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John M. Smagula, Walter Litten and Scott Dunham

In three commercial fields with a history of low leaf P concentrations, triple super phosphate (TSP) (1 P: 0 N), monoammonium phosphate (MAP) (2.1 P: 1 N), and diammonium phosphate (DAP) (1.11 P: 1 N) with P at 67.2 kg·ha-1 were compared to a control in a randomized complete-block design with 12 blocks. In 1995, all fertilizer treatments were comparable in raising soil P concentrations, but MAP and DAP resulted in higher P leaf concentrations compared to the control. DAP was more effective than MAP in raising N leaf concentrations. Leaf concentrations of Mg, B, and Cu were lowered by MAP and DAP but not TSP. Stem density, stem length, flower buds per stem, flower bud density, and yield were raised by DAP. The same treatments were applied in May 1997 and in May 1999 to the same plots in the same fields. In 1997, by the time of tip dieback in the prune year of that cycle, foliar concentration of P and N averaged higher than in the previous cycle, but still were not up to the standard for N. Fruit yield for the second cycle averaged substantially higher for the controls and for all three treatments, most dramatically for the DAP. In 1999, with only two fields available, response to treatments depended on soil N availability. At the field where leaf N was lower in control plots, MAP and DAP were more effective than TSP in raising leaf P.

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Paul E. Cappiello and Scott W. Dunham

Seven Vaccinium angustifolium clones were tested for low-temperature tolerance over two dormant seasons. Flower primordia in the pseudoapical bud were damaged at higher temperatures than were stem tissue and primordia of the fourth floral bud. The flower primordia located at the stem tip also reacclimated earlier and seemed to show a stronger response to abrupt spring warming than did other tissues tested. Given the lowest survival temperatures determined and the ambient temperatures recorded, we recommend that the physiological and economic aspects of cryoprotectants and flower-delaying treatments be studied further.

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Youzhi Chen, John M. Smagula, Walter Litten and Scott Dunham

Twenty stems with four fruit buds were tagged in each of ten lowbush blueberry (Vaccinium angustifolium Ait.) clones in a commercial field to assess fruit set and fruit size and weight characteristics. The terminal bud produced the fewest blossoms and fruit but fruit set was equal among all buds (65%–70%). Fruit at bud 4 were slightly smaller in diameter and weighed less than those produced at other buds. Clones with buds producing more blossoms per bud tended to produce more fruit per bud (pearson corr. coeff., r = 0.49), but a stronger correlation was found between fruit set and fruit number (r = 0.81).

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Youzhi Chen, John M. Smagula, Walter Litten and Scott Dunham

In a managed field of native Vaccinium angustifolium Ait. clones, the effect of fall foliar sprays of B at 345 g·ha-1 and/or Ca at 3,450 g·ha-1 in remedying tissue deficiency of B varied among 12 clones, as seen in pollen germinability and on individual stems as seen in flower number, fruit set, and number of harvestable berries. With Ca applied alone, increased berry size did not overcome yield reduction due to fewer flowers and berries per stem. Berry diameter and mass correlated better to number of seeds of germinable size than to total number of seeds. Pollen germination averaged 17.4% on stigmata from untreated clones, and all three treatments (B, Ca, B + Ca) increased that average by 8%. More seeds per berry with the B-alone treatment implies more ovules fertilized when B deficiency is remedied. No relation was found between in vitro and in vivo pollen germination.