Day-neutral strawberries have the potential to fruit throughout the growing season as long as maximum air temperatures do not exceed 32.2 °C for extended periods. Appropriate temperatures for season-long production of day-neutrals occur in the southern Appalachians at 900 m elevations and above. Replicated studies were conducted at Laurel Springs (900 m elevation) in northwestern N.C. in 2002–04 to determine the most promising combinations of mulch types, planting dates and cultivars. Plasticulture establishment recommendations were followed and white/black plastic mulch compared to black. Dormant plants were established 15 Apr., 1 May, or 15 May at 12 × 12 inch spacing in 2002; plug plants on 30 Oct. 2002 at 12 × 12 inches and overwintered under rowcovers for 2003; and plug plants on 25 Sept. 2003 or 23 Oct. 2003 at 18 × 12 inches and overwintered under rowcovers for 2004. Plants came from commercial sources. Aromas, Diamante, Everest, and Seascape were included in 2002; Diamante, Everest and Seascape in 2003; and Everest and Seascape in 2004. Harvest season lasted 11 weeks in 2002, 12 weeks in 2003, and 10 weeks in 2004. Only main effects were statistically significant. White and black plastic mulch yields were significantly higher than black two years out of three. Fall planting resulted in earlier onset of production and higher yields in most cases. Planting date was important; for fall planting, midto late September was superior to October planting, and for spring planting, middle to late April was superior to mid-May. A plant spacing of 18 inches between plants in rows and 12 inches between rows was important to avoid crowding when planting in fall. Everest and Seascape had the best overall performance.
The genus Kalmia L. is endemic to North America. Kalmia latifolia is the best known species in the genus. It is a rounded evergreen shrub to small tree that ranges from northern Florida to New England. Flower color varies from white to pink, but at lower elevations in the southeastern U.S., pink flowers quickly fade to white. It is a diploid species with 2n = 2x = 24 chromosomes. Kalmia angustifolia var. caroliniana only occurs in the southeastern US. It is a thin upright evergreen shrub to 1.5 m tall. Flower color is either light pink or rosy purple, and the flower pigments appear to be heat stable. It is also diploid. Kalmia latifolia has not crossed readily with any other Kalmia species to date, but a small number of hybrids have been produced. The objective of the present study was to intercross K. angustifolia var. caroliniana with K. latifolia to attempt to develop color stable pink flowered Kalmia hybrids for warm climates. The crosses were made at Cary, N.C., from late April through mid May and included two clones of each species. Only one parental combination was successful and involved a rosy purple form of the former species. With this cross 15 mature seed capsules resulted from 38 pollinations. Numerous seedlings initially germinated, of which about 15% were albinos. Only 38 seedlings survived to transplanting. Thirty seedlings remain relatively vigorous 8 months after potting and are phenotypically intermediate between the parents. Their potential will depend on their ornamental characteristics once they reach maturity.
Thirty-three accessions of Fragaria virginiana collected from Mississippi in 1995 were evaluated for horticultural traits and leaf disease resistance at Reidsville, N.C., and strawberry anthracnose resistance (Colletotrichum acutatum and C. fragariae) at Poplarville, Miss., in 1997. The range of variability in berry shape, fruit flesh color, fruit skin toughness, and degree of sunkenness of seeds among accessions indicated probable introgression with F. xananassa in most all accessions. Seventeen of 29 accessions screened for resistance to C. acutatum were resistant, and an additional 10 were tolerant. Overall, these accessions appear to be good additional sources of resistance to this, the prevalent species of anthracnose in the southeastern United States. In addition, the majority of accessions appear to be tolerant-resistant to leaf scorch, leaf blight, and/or powdery mildew. Nine accessions were resistant to all three leaf diseases, and four were resistant to C. acutatum as well as the three foliar diseases. No accessions were resistant to C. fragariae and only five were tolerant. All five accessions tolerant to C. fragariae were also either resistant or tolerant to C. acutatum but the converse was not true.
As a first step in determining the phylogeny of the rabbiteye blueberry (Vaccinium ashei Reade), the potential fertility levels among its purported diploid ancestral species. Vaccinium atrococcum (Gray) Heller, Vaccinium caesariense MacKenzie, Vaccinium darrowi Camp, and Vaccinium tenellum Ait., were determined. Differences existed among species in female fertility as determined by total number of seeds and number of potentially viable seeds. The number of seeds per berry was lower than that reported for highbush and rabbiteye blueberry cultivars. No differences were found among species in potential male fertility as indicated by percent stainable pollen. Pollen diameter was not a good criterion for distinguishing species or ploidy levels. Comparison of fertility of diploid species with that of purported polyploid derivatives is suggested as a possible aid in determining phylogeny in Vaccinium. Unreduced pollen grains were detected in only 2 of the 4 species in this study. The average return from heterploid (4n × 2n) crosses was 3 seedlings per 1000 pollinations.
Five southeastern United States diploid Vaccinium species were examined in 1983 and 1984 for pollen viability, unreduced pollen frequency, and pollen diameter. Significant intraspecific variation occurred for all three characteristics. Pollen viability and 2n pollen frequency did not vary significantly among species or between years. The number of clones producing 2n pollen was low, 8 of 41 in 1983 and 3 of 41 in 1984. Vaccinium elliottii Chapm. accounted for at least half of the 2n clones each year and also exhibited the highest unreduced pollen frequencies in 1983 (1.9%) and 1984 (1.6%). All 1984 2n clones were diplandrous the previous year, suggesting a genetic basis for unreduced gamete production. Unreduced pollen was found in three of the five species studied. Pollen diameter was not a good criterion for distinguishing one diploid species from another. Significant pollen diameter differences from 1983 to 1984 may be attributable to differences in pollen storage procedures and not environment per se.
The comparative self-compatibility, intra-, and interspecific crossability of representative clones of V. atrococcum (Gray) Heller, V. caesariense Mackenzie, V. darrowi Camp, and V. tenellum Aiton was determined. The number of germinated seeds and number of vigorous seedlings proved to be the best criteria for evaluation of crossability. The 4 species were largely self-incompatible. Generally, intraspecific and interspecific crossability levels were singificantly higher than those of the self-pollinations. Interspecific crossability was significantly lower than intraspecific crossability. Crossability levels within species and the range in crossability in individual combinations among species were extremely variable. Although F1 hybrids were produced in each of the 6 species hybridizations attempted, the rate of success was highly variable, and the direction in which the cross was made was usually critical. Specific combining ability was considerably more important than general combining ability in achieving species hybridizations. The hypothesis of complete homoploid interfertility in Vaccinium was not valid for these 4 species. The ranking of species crossability (number of vigorous seedlings per 100 pollinations) from highest to lowest was: V. atrococcum – V. caesariense, V. atrococcum – V. darrowi, V. darrowi – V. tenellum, V. caesariense – V. tenellum, V. caesariense – V. darrowi, and V. atrococcum – V. tenellum.
A 24 or 48 hour soak in gibberellins (GA) did not influence the total germination of open-pollinated rabbiteye blueberry seeds (Vaccinium ashei Reade, cv. Tifblue). GA4+7 at 100-500 ppm stimulated early germination of seeds from the 2nd to 4th week after sowing, with the maximum effect occurring after 3 weeks. The 48-hour, GA4+7, 100 ppm treatment stimulated germination from the 2nd to 5th week after sowing. Stimulation of earlier germination by GA4+7 hastened seedling transplanting by 2 to 4 weeks. Germination of mature seeds (large, filled) was significantly higher than immature (medium-size, filled) or imperfectly (partially-filled) developed seeds. GA4+7 did not increase germination of immature or imperfectly developed seeds.
Fifty seedlings each of 8 tetraploid interspecific populations involving 6 Vaccinium species were examined for date of flowering, date of fruit ripening, fruit yield, color, firmness, and size. The 8 progenies contained from 25 to 75% highbush blueberry (V. corvmbosum L.) germplasm. There were significant differences among the 8 populations for all fruit characters and for the number of days from bloom to ripe fruit. Only 2 backcross progeny populations (75% high-bush blueberry) produced significant numbers of seedlings that met the selection criteria for 4 fruit characters.