Efforts are underway to develop genetic linkage maps for two interspecific blueberry populations (Vaccinium darrowi × V. elliottii and V. caesariense-derived populations). To date, 72 RAPD markers have been mapped, and another 200 markers have been identified as suitable for mapping in the V. darrowi × V. elliottii-derived population. Inheritance of 40 RAPD markers has been followed, and additional 40 RAPD markers have been identified as suitable for mapping in the V. darrowi × V. caesariense population. These two populations are comprised of individual plants that should have a wide range of chilling requirements. At a later date, plants will be classified according to their chilling requirements to identify RAPD markers that cosegregate with chilling requirements. Presently, a bulked-segregant analysis is being performed on a tetraploid breeding population (primarily V. corymbosum) to identify RAPD markers linked to chilling requirement genes.
In the 1970s, the U.S. Department of Agriculture (USDA) began developing low-chill-adapted highbush blueberry (Vacchizium corymbosum L.) for the southern United States (lat. 29° to 32°N) by using germplasm of the native southern species, V. darrowi Camp. This breeding work resulted in the release of several low-chill southern highbush blueberry (SHB) cultivars in the mid-1980s. These cultivars have been evaluated for yield and adaptation at several locations through the southern regional blueberry germplasm evaluation trials. These trials have shown that organic mulch is required for good performance of SHB. The one-fourth V. darrowi composition of SHB cultivars presents problems of freeze damage at some locations. This problem may be resolved by breeding cultivars through several alternative approaches.
Fifteen highbush (or highbush hybrid) blueberry cultivars (Vaccinium corymbosum Linnaeus), two rabbiteye blueberry cultivars (V. ashei Reade), and one southern lowbush (V. darrowi Camp) selection from the wild were examined using seventeen 10-base RAPD and seven 15- to 18-base SSR-anchored primers (primers comprised of SSR motifs) in polymerase chain reactions (PCRs). Fifteen RAPD and three SSR markers resulting from these reactions were chosen to construct a DNA fingerprinting table to distinguish among the genotypes included in this study. Similarity values were calculated based on 132 RAPD and 51 SSR bands, and a dendrogram was constructed based on the similarity matrix. The V. ashei cultivars and V. darrowi selection grouped out separately from the V. corymbosum cultivars as expected. However, estimates of relative genetic similarity between genotypes within the V. corymbosum group did not agree well with known pedigree data and, thus, indicated that RAPD and SSR data did not accurately assess the genetic relationships of cultivars within this species.
A tetraploid blueberry population resulting from a cross of US 75 {a tetraploid hybrid of Fla 4B [a selection of Vaccinium darrowi Camp (2n = 2x = 24) × `Bluecrop' [(V. corymbosum L. (2n = 4x = 48)]} × `Bluetta' (4x) was used to generate a genetic linkage map of US 75 by randomly amplified polymorphic DNA (RAPD) analysis. One hundred and forty markers unique for Fla 4B that segregated 1:1 in the population were mapped into 29 linkage groups that cover a total genetic distance of 1288.2 cM, with a range of 1.6 to 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 used. Therefore, all the chromosomes of V. darrowi could be represented in the map.
Abstract
V. myrsinites Lam. is most susceptible to canker among the blueberry species native to Florida and survives by resprouting from underground rhizomes. V. darrowi Camp suffers less canker damage than V. myrsinites, some mature colonies showing little or no damage but others being nearly destroyed by the disease. Most mature V. darrowi colonies in the State have some stems cracked and swollen by canker. Old native plants of V. ashei Reade and V. fuscatum Ait. show light to moderate canker damage in many parts of the State but both species are more resistant than the previous two. V. elliottii Chapm. shows no canker over much of its range in Florida, but localized populations have moderate to high infection. Only one cankered plant of V. arborewn Marsh, has been found, and no canker has been found on V. stamineum L.
Abstract
Pollen morphology of 10 Vaccinium species, 10 interspecific hybrids, and 3 colchicine-induced polyploids were studied using scanning electron microscopy. Size, exine patterning, furrow and pore size and shape, and general appearance were investigated. Although differing morphological features were generally lacking, some interspecific differences and variation within hybrid populations were noted. Furrow and pore sizes, and the associating opericuli were the most valuable characters. Some species had large furrows with large rounded pores and others had small furrows with insignificant pores. Exine patterning was minimal and, when present, generally occurred in the inter-colporate regions. F1 populations of V. corymbosum × V. elliottii had the greatest exine variation and the degree of exine patterning revealed a possible dosage effect. Exine patterns suggest that the ancestors of V. myrsinites may be V. darrowi and V. elliottii rather than V. darrowi and V. tenellum as previously proposed by Camp.
Abstract
Adaptation to upland soils was investigated in a diallel study involving progeny of 4 blueberry (Vactinium) clones consisting of 1 highbush blueberry (V. corymbosum L.) clone and 3 interspecific hybrids. Both general and specific combining ability were significant. Seedling progenies of NJUS 11 (V. ashei × V. atrococcum) and US75 (V. darrowi × V. corymbosum) grew well on an upland soil. Although not included in the diallel crosses, NJUS 64 (V. myrsinites × V. angustifolium) progenies also grew well on upland soil.
Abstract
Three pentaploids produced from hybridizing hexaploid Vaccinium ashei Reade and diploid V. darrowi Camp were analyzed for fruit set, number of seeds/fruit, seedlings/pollination, pollen grains/sporad, 2n gamete production, pollen germination, leaf area and berry weight, color, scar, and firmness. The pentaploids were intermediate between the parental species in fruit size and leaf area. There was high variation in fertility and in fruit quality among the pentaploid hybrids.
Loss of freeze tolerance, or deacclimation, is an integral part of winter survival in woody perennials because untimely mid-winter or spring thaws followed by a hard freeze can cause severe injury to dehardened tissues. This study was undertaken to investigate deacclimation kinetics, particularly the timing and speed, of five blueberry (Vaccinium L.) cultivars (`Bluecrop', `Weymouth', `Ozarkblue', `Tifblue', and `Legacy'), with different germplasm compositions and mid-winter bud hardiness levels, in response to an environmentally controlled temperature regime. Based upon bud cold hardiness evaluations in 2000 and 2001, `Tifblue', a Vaccinium ashei Reade cultivar, was one of the least hardy and the fastest to deacclimate; `Bluecrop', a predominantly V. corymbosum L. cultivar, was the most hardy and the slowest to deacclimate; and `Ozarkblue', a predominantly V. corymbosum cultivar but including southern species V. darrowi Camp. and V. ashei, was intermediate in speed of deacclimation. `Weymouth' (predominantly V. corymbosum) and `Legacy' (73.4% V. corymbosum and 25% V. darrowi) were slow to intermediate deacclimators. Deacclimation rates did not correlate strictly with mid-winter bud hardiness. Data suggest that the southern germplasm component V. ashei may be responsible for the observed faster deacclimation whereas both southern species, V. darrowi and V. ashei, may contribute genes for cold sensitivity. Strong positive correlations between stage of bud opening and bud cold hardiness existed in both years (r = 0.90 and 0.82 in 2000 and 2001 study, respectively). Previously identified major blueberry dehydrins, 65-, 60-, and 14-kDa, progressively decreased in their abundance during incremental dehardening in `Bluecrop', `Weymouth', and `Tifblue'. However, down-regulation of the 14-kDa dehydrin most closely mirrored the loss in cold hardiness during deacclimation, and, therefore, may be involved in regulation of bud dehardening. Because differences in deacclimation rate were clearly evident among the genotypes studied, rate of deacclimation of the flower buds of blueberry should be an important consideration in breeding to improve winter survival.
Inbreeding coefficients were calculated for highbush blueberry (Vaccinium corymbosum L.) cultivars based on a tetrasomic inheritance model. This model yielded lower inbreeding coefficients than previous calculations based on a disomic tetraploid inheritance model. Recent trends in breeding have resulted in significant use of V. darrowi Camp as a source of low-chilling germplasm for use in the southern United States. There is also a trend toward increased inbreeding in several crosses from which recently released cultivars have been derived. Increased inbreeding coefficients do not represent a detrimental situation in blueberry per se.