Genomic differentiation and evolution in blueberry: An examination of an interspecific hybrid of diploid Vaccinium darrowi and tetraploid V. corymbosum

A series of experiments were conducted to study the genomic differentiation and evolution of blueberry using an interspecific hybrid, US 75, derived from Fla 4B (a wild selection of Vaccinium darrowi (2x)) x 'Bluecrop' ((a cultivar of V. corymbosum (4x)).; US 75 was found to contain about 70% of Fla 4B's heterozygosity, a value attributed to a first division restitution (FDR) mode of 2n gamete production. Crossovers during 2n gamete formation were evidenced by the absence of 33 dominant alleles of Fla 4B in US 75, and direct tests of segregation in a diploid 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 tetraploid segregating population of US 75 x V. corymbosum cv. 'Bluetta'. Sixty-five duplex loci were identified which segregated in a 5:1 ratio, indicating US 75 undergoes tetrasomic inheritance.; Second, a genetic linkage map of US 75 was generated. One hundred and forty markers unique for Fla 4B that segregated 1:1 in the tetraploid population were mapped into 29 linkage groups that cover a total genetic distance of 1288.2 cM, with a range 1.6-33.9 cM between adjacent markers. The map is essentially of V. darrowi because US 75 was produced via a 2n gamete from Fla 4B and only unique markers for Fla 4B were utilized.; Third, the meiotic pairing configurations and genomic similarity of US 75 and its (GISH). US 75 was found to have a lower than expected number of multivalents for an autopolyploid, but it had a significantly higher number of quadrivalents than V. corymbosum, and one PMC (pollen mother cell) was observed with 11 of all 12 homologous groups being paired in quadrivalents. Normal distributions of chromosomes were observed at anaphase I and II by both cytological observation and pollen viability. GISH revealed that both parents labeled all the chromosomes in the hybrid.; Finally, four new mechanisms of 2n pollen formation were found in blueberry by examining the cytogenetics of PMCs and sporad configurations of selfed progenies of US 75. These were: (1) Premeiotic doubling (PD), where chromosome doubling in a PMC during mitosis resulted in the formation of four 2n gametes; (2) Tripolar spindle (TPS), where the spindles at anaphase II were fused at one pole resulted in one 2n and two n gametes; (3) Incomplete spindle at anaphase I (IS1), where the spindle functioned briefly at anaphase I and then failed producing two 2n gametes; and (4) Incomplete spindle at anaphase II in one daughter nuclei (IS2-1), where the spindle at anaphase II in one daughter nuclei functioned briefly and then failed resulting in one 2n and two n gametes. (Abstract shortened by UMI.)...