Irregular germination and delayed emergence of blueberry, strawberry, blackberry and raspberry seedlings have been noted by various investigators. Seed treatments such as afterripening (1) and acid scarification of strawberry seed (2) improved rapidity of germination, but neither treatment fully overcame the delay in seed germination. In a study with blueberry seed, after-ripening did not improve germination (2). Sporadic germination and delayed emergence of seedlings complicates a breeding program when uniform size of seedlings is desired.
Three blueberry progenies from crosses of large-fruited X large-fruited parents were significantly larger in fruit size than 3 progenies from crosses of large-fruited X small-fruited parents. Mean fruit sizes of the 3 large-fruited X small-fruited populations were equal to the fruit size of the smaller fruited parents in each cross, indicating that small fruit size is a dominant character. Large fruit size is not linked with low yield.
Chromosome pairing in a derived decaploid, 2n=10×=120, (from a colchicine-treated, sterile pentaploid hybrid of Vaccinium ashei Reade × V. corymbosum L.) was chiefly bivalent. Multivalent associations were present in 5 of 16 cells scored at metaphase I, but only 23 chromosomes of the 1,920 observed were involved in multiple pairing. Most of the cells at anaphase I (33 of 35 observed) contained lagging chromosomes which appeared to be non-disjoined bivalents rather than univalents. The decaploid was selfed and crossed with hexaploid, tetraploid, and diploid species. The mean number of seedlings produced per flower pollinated for each ploidy level was low, ranging from 0.04 to 0.09. The mean seedling number produced per self-pollinated flower was considerably higher, 0.92. The percent of pollen which stained in propionocarmine was 8% for the pentaploid parent, 62% for the derived decaploid and 99% for plants of V. ashei and V. corymbosum used as standards for comparison.
Iron chlorosis often develops in blueberries (Vaccinium) grown on soils with a pH above 5.2. Seedlings of 4 blueberry intra- and interspecific progenies, involving V. ashei, V. corymbosum, and V. darrowii, were tested for Fe-efficiency (use of Fe) by growing them in nutrient solutions containing different concentrations of CaCO3 to vary the pH. Plants received Fe during the first 4 harvests (up to 75 days) but received no Fe during the subsequent 2 harvests. The Fe supply for plant growth in the last 2 harvests was limited to that available in the roots. T-65 × US 67 blueberry plants [a 3-species hybrid of V. ashei × (V.darrowii × V. corymbosum)] lowered the pH of the nutrient solution by releasing H+ from their roots which freed Fe from root accumulations and made it available for plant use. ‘Climax’ × T-151 (V. ashei × V. ashei) progeny did not do this. Seedlings of V. corymbosum and those from a cross of V. corymbosum with V. darrowii were intermediate in their response.
Studies were conducted on the feasibility of shortening the evaluation period of highbush blueberry (Vaccinium corymbosum L.) selections by propagating by softwood cuttings taken from each of the single-plant selections at the time of fruit evaluation row the following spring. Softwood cuttings were taken from a single plant of 5 early, 5 midseason, and 5 late ripening selections in June, July, and August. July cuttings (60%) rooted better than June (37%) and August (31%) cuttings. Early selections (34%) rooted about the same as midseason (32%) and late (35%) selections. The earlier the cuttings were potted, the larger the root system they developed before frost when grown in an unheated greenhouse. None of the rooted cuttings potted 30 Sept, developed root systems large enough to survive field planting. Supplemental heat and light after potting increased root growth of plants potted 25 Aug. but not those potted 10 Sept. Eighty percent of the plants transplanted to the field survived.
In a germination test with strawberry seed of different ages stored at 40°F, 23-year-old seed germinated as well as 1-year-old seed. Germination was relatively high for all of the seed lots, despite differences in age.
In a study of breeding of strawberry (Fragaria × ananassa Duch.) for resistance to red stele root rot caused by Phytophthora fragariae Hickman, two different composites of races of the fungus were used to screen seedlings, one with and one without race A-5. In the absence of race A-5, all resistant parents produced between 28.6 to 72.0% resistant seedlings depending upon parental combinations. When race A-5 was included in the composite, two breeding selections that were derived from Fragaria chiloensis Yaquina A clone transmitted more resistance to their seedlings than three other parents in a diallel comparison. Mean squares and variance components were higher for general than for specific combining ability. Resistance is partially dominant for the races involved in this study.
Inheritance of albino seedling was studied in progenies of 3 tetraploid cultivated highbush blueberry clones. This mutant character was found to be controlled by a recessive gene at a single locus. All 3 parental clones appeared to be duplex (AAaa) for the marker gene and upon crossing and selfing segregated with ratios that are most likely to occur with tetrasomic inheritance. They segregated approximately 43 normal : 1 albino which is a significant deviation from the expected 35:1 ratio. This deviation is probably due to nonrandom pairing at meiosis of the 4 homologous chromosomes bearing the marker gene.
A clone of the diploid blueberry species Vaccinium atrococcum Heller, was previously found to be highly resistant to the fungus tetraploid highbusy blueberry. The tetraploid V. atrococcum was highly root-rot resistant in a greenhouse study. It was crossed with ‘Earliblue’ and 85 seedlings were obtained. In general, the seedlings were fertile, had small, dark fruit with mild flavor, good scars and quite soft flesh consistency.
Blueberry selections Me-US 32 and Michigan Lowbush 1, and cultivars ‘Berkeley’, ‘Bluecrop’, ‘Earliblue’, and ‘Dixi’ were screened in the greenhouse for resistance to P. cinnamomi. Michigan Lowbush 1 was highly resistant to the root-rot fungus. Me-US 32 was resistant, but all the cultivars were susceptible. Michigan Lowbush 1 is a grandparent and probably the source of resistance of Me-US 32.
‘Spartan’ highbush blueberry (Vaccinium corybosum L.) is a new cultivar resulting from the cooperative efforts of Michigan grower Arthur Elliott, the Michigan Blueberry Grower’s Association, and the Science and Education Administration, of USDA.