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Elliot H. Norden, Paul M. Lyrene, and Jose X. Chaparro

A progeny of 55 blueberry seedlings produced by pollinating 4301 flowers of tetraploid highbush blueberry cultivars with pollen from 19 different diploid Vaccinium elliottii plants was studied to determine hybridity and ploidy. Of the 21 seedlings whose phenotypes were intermediate between parental types, indicating hybridity, 18 were triploid and three were tetraploid. Pollen of the triploids, when viewed at ×250, was almost all shrunken and aborted, although some triploid hybrids produced a few large, plump microspores in dyads or monads. Triploids produced no seed when pollinated with pollen from 4x highbush or 2x V. elliottii or when open-pollinated outside the greenhouse in the presence of fertile diploid and tetraploid blueberries. Tetraploid hybrids produced large populations of vigorous seedlings when intercrossed. Both triploid and tetraploid F1 hybrids were intermediate between the parents in leaf size and flower size. The triploids produced no berries; the tetraploids were intermediate between the parents in berry size but averaged lower in Brix and berry firmness than either parent. Seven additional F1 hybrids from reciprocal crosses were obtained by pollinating 2309 flowers of 2x V. elliottii with pollen from tetraploid highbush cultivars. Although five V. elliottii clones served as female parents in these crosses, only one produced any seedlings. Six of the seven hybrids flowered and were fertile tetraploids; one was a sterile triploid.

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Thomas G. Beckman, Jose X. Chaparro, and Wayne B. Sherman

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Dennis J. Werner, Michael A. Creller, and José X. Chaparro

Inheritance of the blood-flesh (red-violet mesocarp) trait in peach [Prunus persica (L.) Batsch.] was investigated in S1, S2, F1, F2, F3, BC1P1, and BC1P2 families derived from `Harrow Blood', a clone showing anthocyanin accumulation in fruit about 45-50 days after anthesis. This trait invariably was associated with the red midrib leaf phenotype in `Harrow Blood', an S1 family from `Harrow Blood', and in green leaf F2 progeny derived from `Harrow Blood' × `Rutgers Red Leaf 2n'. A segregation ratio of about 3 blood-flesh : 1 wild-type was observed in the S1 family, but F1 progeny produced only wild-type fruit. Examination of F2 progeny segregating for the blood-flesh and red leaf traits revealed no evidence of epistasis. Based on segregation ratios in F1, F2, F3, BC1P1, and BC1P2 families from this cross, the F1 family from `Contender × (`Harrow Blood' × `Rutgers Red Leaf 2n'), and six additional F1 families from crosses between `Harrow Blood' and green leaf clones with wild-type fruit, we propose that blood-flesh is controlled by one gene, designated bf (blood-flesh). The blood-flesh phenotype was associated with reduced tree height in S1 and F2 progeny derived from `Harrow Blood'. Segregation for leaf blade color deviated significantly (P = 0.05) from the expected 3 red : 1 green ratio in six of the F2 families derived from selfing seven F1 trees from `Harrow Blood' × `Rutgers Red Leaf 2n'.

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Dario J. Chavez, Eileen A. Kabelka, and José X. Chaparro

Phytophthora capsici causes seedling death, crown and root rot, fruit rot, and foliar blight on squash and pumpkins (Cucurbita spp. L.). A total of 119 C. moschata accessions, from 39 geographic locations throughout the world, and a highly susceptible butternut squash cultivar, Butterbush, were inoculated with a suspension of three highly virulent P. capsici isolates from Florida to identify resistance to crown rot. Mean disease rating (DR) of the C. moschata collection ranged from 1.4 to 5 (0 to 5 scale with 0 resistant and 5 susceptible). Potential resistant and tolerant individuals were identified in the C. moschata collection. A set of 18 PIs from the original screen were rescreened for crown rot resistance. This rescreen produced similar results as the original screen (r = 0.55, P = 0.01). The accessions PI 176531, PI 458740, PI 442266, PI 442262, and PI 634693 were identified with lowest rates of crown infection with a mean DR less than 1.0 and/or individuals with DR = 0. Further selections from these accessions could be made to develop Cucurbita breeding lines and cultivars with resistance to crown rot caused by P. capsici.

Open access

Shirin Shahkoomahally, Jose X. Chaparro, Thomas G. Beckman, and Ali Sarkhosh

The rootstock is an essential element for orchard management, influencing scion growth, nutrient concentration, and fruit quality. Seasonal variations in leaf nutrients of ‘UFSun’ grafted on five different rootstocks (‘Flordaguard’, ‘Barton’, ‘MP-29’, ‘P-22’, and ‘Okinawa’) were investigated during the 2017–18 growing season in Citra, FL. There was no significant variation in the macronutrient concentrations (N, P, K, Mg, Ca, and S) among different rootstocks; however, ‘UFSun’ on ‘Okinawa’ and ‘Flordaguard’ showed greater concentrations of Ca, K, and Mg concentration than other rootstocks. In contrast, ‘Flordaguard’ showed less potential to accumulate P as compared with other rootstocks. The Ca concentration was lowest in ‘MP-29’ and ‘Barton’ in April and June. The concentration of macronutrients (N, P, K, Mg, Ca, and S) in leaves was greater in April and October than in December and June. With respect to rootstocks, macronutrients in December and June were the highest in ‘Okinawa’ and the lowest in ‘Barton’. In April, the lowest concentration of macronutrient was recorded in ‘Barton’, whereas the highest concentrations were found in ‘P-22’, ‘Okinawa’, and ‘Flordaguard’. The highest leaf micronutrient concentrations were found in ‘MP-29’ and ‘Barton’, and the lowest in ‘Okinawa’ and ‘Flordaguard’ in June and October. For all rootstocks, concentrations of micronutrients increased between leaf growth in April and senescence in October. The micronutrient concentrations of leaves decreased during December. The widest dynamic changes during the vegetative cycle were found on ‘P-22’. Seasonal trends were more consistent for micronutrients than for macronutrients.

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Dario J. Chavez, Thomas G. Beckman, and José X. Chaparro

Prunus phylogeny has been extensively studied using chloroplast DNA (cpDNA) sequences. Chloroplast DNA has a slow rate of evolution, which is beneficial to determine species relationships at a deeper level. The chloroplast-based phylogenies have a limitation due to the transfer of this organelle by interspecific hybridization. This creates difficulties when studying species relationships. Interspecific hybrids in Prunus occur naturally and have been reported, which creates a problem when using cpDNA-based phylogenies to determine species relationships. The main goal of this project was to identify nuclear gene regions that could provide an improved phylogenetic signal at the species level in Prunus. A total of 11 species in Prunus and within section Prunocerasus were used. Two peach (Prunus persica) haploids were used to test the reliability of the molecular markers developed in this project to amplify single-copy genes. A total of 33 major genes associated with vernalization response, 16 with tree architecture, and 3 with isozymes, were tested. Similarly, 41 simple sequence repeat (SSR) markers, seven cpDNA regions, and the internal transcribed spacer (ITS) region, were used. Multiple gene regions were identified and provided the greatest number of characters, greatest variability, and improved phylogenetic signal at the species level in Prunus section Prunocerasus. Out of those, trnH-psbA, PGI, MAX4, AXR1, LFY, PHYE, and VRN1 are recommended for a phylogenetic analysis with a larger number of taxa. The use of potentially informative characters (PICS) as a measure of how informative a region will be for phylogenetic analyses has been previously reported beneficial in cpDNA regions and it clearly was important in this research. This will allow selecting the region(s), which can be used in phylogenetic studies with higher number of taxa.

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Todd W. Wert, Jeffrey G. Williamson, Jose X. Chaparro, E. Paul Miller, and Robert E. Rouse

The effect of climate was observed on fruit quality of four low-chill peach cultivars (Flordaprince, Flordaglo, UFGold, and TropicBeauty). The cultivars were evaluated in three locations (north–central, central, and southwest Florida). Soluble solids content (SSC), titratable acidity (TA), SSC:TA ratio, fruit weight, blush, and fruit development period (FDP) were determined. Longer FDPs were observed at the north–central location than at the southwest location. Fruit development and the expression of quality attributes were affected by location during fruit growth with higher color and SSC and shorter FDP occurring under warmer conditions. Within locations, ‘UFGold’ had the shortest FDP except at the southwest location where its chilling requirement may not have been met. At the central and southwest locations, ‘UFGold’ also tended to have lower TA values and higher SSC;TA ratios than the other cultivars.

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Gerard W. Krewer, Thomas G. Beckman, Jose X. Chaparro, and Wayne B. Sherman

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Todd W. Wert, Jeffrey G. Williamson, José X. Chaparro, E. Paul Miller, and Robert E. Rouse

Fruit shape of four low-chill peach [Prunus persica (L.) Batsch] cultivars was evaluated in north-central, central, and southwest Florida. During 2005, measurements were taken at all locations for cheek diameter, suture diameter, and tip protrusion. A suture deformation index was calculated (suture diameter/cheek diameter) to determine suture deformation. Fruit had more protruding tips and suture deformation was more pronounced at the southwest location than at the north-central or central locations. Overall, ‘TropicBeauty’ had more protruding tips than the other cultivars. It was concluded that warmer temperatures at the southwest location during fruit development affected fruit shape by increasing the incidence of protruding tips and pronounced sutures.

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Todd W. Wert, Jeffrey G. Williamson, Jose X. Chaparro, E. Paul Miller, and Robert E. Rouse

The effect of climate was observed on the relative frequency of vegetative and floral buds in four low-chill peach cultivars (‘Flordaprince’, ‘Flordaglo’, ‘UFGold’, and ‘TropicBeauty’). The trees were planted in north–central, central, and southwest Florida. The percentage of blind nodes, mixed nodes (nodes with vegetative and floral buds), and nodes with only vegetative buds were determined from three representative shoots per tree at each location. In general, higher percentages of blind nodes were observed in central and southwest Florida and higher percentages of mixed nodes were observed in north–central Florida. ‘TropicBeauty’ tended to have a greater percentage of blind nodes than the other cultivars. Higher temperatures during bud formation most likely contributed to the increased amounts of blind nodes observed in the central and southwest locations and to the reduced amounts of mixed nodes. However, stresses imposed by bacterial spot and hurricanes may have contributed to the higher incidence of blind nodes in 2005. Our results indicate that certain genotypes have a predisposition for the formation of blind nodes. Advanced selections having low chilling requirements and potentially being adapted to a wide diversity of tropical or subtropical climates need to be tested in multiple locations to evaluate blind node formation.