Mark K. Ehlenfeldt

Fertility of somatic hybrids from protoplast fusions of Solanum brevidens and S. tuberosum.

SummaryTwo sets of somatic hybrids between Solanum brevidens (2x) and S. tuberosum (2x and 4x) were evaluated for male fertility, meiotic regularity and female fertility. The somatic hybrids were tetraploids from 2x + 2x fusions and hexaploids from 2x + 4x fusions. Pollen stainability ranged from 0 to 83% in tetraploids and from 0 to 23% in hexaploids. The tetraploids had more regular meiosis, lower levels of micropollen and fewer unassociated chromosomes than hexaploids. However, except for a low level of selfing, the pollen of both sets of hybrids was ineffective in pollinations. The tetraploids, as females, crossed poorly with 2x and 4x tester species and selfed only at low levels. The hexaploid fusion hybrids also crossed poorly with the 2x tester species and selfed only to a limited degree; however, they crossed well with 4x testers. Seed set in crosses with S. tuberosum Group Andigena, and S. tuberosum Group Tuberosum cultivars ‘Kathadin’ and ‘Norland’ averaged 16.7, 15.6 and 28.6 seeds per fruit, respectively. Progeny from these crosses had 5x or nearly 5x ploidy levels. The results indicate that reasonable levels of female fertility can be obtained in somatic fusion hybrids of S. brevidens and S. tuberosum.

Sexual progeny of somatic hybrids between potato andSolanum brevidens: Potential for use in breeding programs

Hexaploid somatic hybrids have been obtained by fusion of protoplasts fromSolanum brevidens (PI 218228, 2x = 2n = 24) andS. tuberosum (PI 203900 or cv. Russet Burbank; 2x = 4n = 48). In the work reported here, pentaploid progeny derived from sexual crosses between the somatic hybrids and the potato cultivar, Katahdin were assessed for transfer of disease resistances and improvement of agronomic traits. Segregation was noted in disease resistances to race 0 ofPhytophthora infestans and to tuber soft rot caused byErwinia spp., indicating that sexual transfer of traits captured by protoplast fusion had occurred. The pentaploid progeny showed substantial variation in and often improvement of some agronomic traits as compared to the somatic hybrids. The results indicate that interspecific somatic hybridization can produce material with potential for use in a potato breeding programCompendioSe han obtenido híbridos somáticos hexaploides por fusión de protoplastos deSolanum brevidens (PI218228, 2x = 2n = 24)yS. tuberosum (PI203900 o cv Russet Burbank; 2x = 4n = 48). En el trabajo, cuyo informe se presenta aquí, las progenies pentaploides se obtuvieron de cruzamientos sexuales entre los híbridos somáticos y el cultivar de papa Katahdin y se evaluaron para transferencia de resistencias a enfermedades y el mejoramiento de atributos agronómicos. Se notó segregación en las resistencias a enfermedades, a la raza 0 dePhytophthora infestans y a la pudrición suave de los tubérculos causada porErwinia spp., indicando que la transferencia sexual de atributos capturada al usar fusión de protoplastos había ocurrido. En comparación con los híbridos somáticos, la progenie pentaploide mostró una variatión sustancial, y frecuentemente, la mejora de algunos atributos agronómicos. Los resultados indican que la hibridación somática interespecífica puede producir material con potencial para ser utilizado en un programa de mejoramiento de papa.

Intra-specific fusions in Solanum tuberosum

SummaryPlants were regenerated from callus arising from protoplast fusion of two S. tuberosum diploids. Tetraploid progeny from the fusion of the two diploid partners had increased vigor. Isozyme analysis confirmed the presence of proteins from both partners in the fusion progeny. Pigmentation of tubers and anthers was heightened substantially in the fusion products. This fusion, the first intra-specific fusion within S. tuberosum, indicates that somatic fusion may be useful for transferring traits within this group.

Anthracnose Fruit Rot Resistance in Blueberry Cultivars

Anthracnose fruit rot (causal agent, Colletotrichum acutatum) is an important disease in most blueberry growing regions of North America. Losses caused by the disease are usually seen as a postharvest rot with orange spore masses appearing on the surface of affected fruit. One hundred cultivars/selections of blueberry were screened for resistance to fruit rot between 1993 and 2003 by inoculating container-grown plants bearing green fruit. Visible rot symptoms on ripe fruits were evaluated after a 1-week incubation at room temperature. Our analyses revealed that infection levels were affected by mean May temperatures in New Jersey, generally increasing as temperatures increased; however, this effect was not consistent among all cultivars. A generalized linear mixed model was developed to predict resistance at the historic mean May temperature, conservatively explaining 59% of the variance in resistance. Percent infection ranged from 9 to 91% with a mean of 51% across all cultivars. Results for common cultivars corresponded well with field reports of their relative susceptibilities. An estimate of narrow-sense heritability of 0.32 suggested additive inheritance of resistance. Since very high inoculum loads were used in this study, cultivars exhibiting a low percentage of fruit rot are predicted to show superior field resistance to the disease and will be incorporated into an ongoing breeding program.

Molecular Detection and Discrimination of Blueberry red ringspot virus Strains Causing Disease in Cultivated Blueberry and Cranberry

Blueberry red ringspot virus (BRRV) causes red ringspots on the stems, leaves, and ripening fruit of infected highbush blueberry (Vaccinium corymbosum) plants. The disease was originally observed in New Jersey and has now been reported in other blueberry growing regions in the United States, as well as several locations in Europe. A disease with similar symptoms occurs in American cranberry (V. macrocarpon), but BRRV has never been confirmed as the causal agent. Serological detection of BRRV in infected plants has been unsatisfactory. Using a primer set designed for routine detection (RRSV3/RRSV4), we successfully amplified a fragment of the virus from all tissues of infected highbush blueberry plants. Using the same primer set, we confirmed natural infection of BRRV in rabbiteye (V. virgatum) blueberry cultivars and the rabbiteye × V. constablaei hybrid cultivar Little Giant. These species have not been previously reported as hosts for this virus. Viral fragments were cloned from representative blueberry and cranberry plants exhibiting ringspot symptoms. Phylogenetic analysis of sequence data showed that cranberry strains of BRRV are precursors to the more derived blueberry strains. The techniques reported in this paper are being used to evaluate strain variation in Vaccinium species and to identify the as yet unknown vector(s) of this virus.

Resistance of Diploid Vaccinium spp. to the Fruit Rot Stage of Mummy Berry Disease

Mummy berry disease caused by Monilinia vaccinii-corymbosi is the most widespread economically important problem of cultivated blueberry in North America. In an attempt to identify new sources of resistance to the fruit rot (mummification) phase of mummy berry, 140 accessions from a total of 21 populations from seven wild diploid species of blueberry were evaluated for resistance under greenhouse conditions. Six isolates of M. vaccinii-corymbosi from three states were used as inoculum. A highly resistant response to mummy berry fruit rot was exhibited by all accessions of Vaccinium boreale, V. myrtilloides, V. pallidum, and V. tenellum, and by most accessions of V. darrowi. Most of the V. corymbosum and V. elliottii accessions were moderately to highly susceptible. Introgression of the resistance found in the wild diploid species into horticulturally desirable cultivars could significantly improve available resistance.

Simultaneous LC-MS quantification of anthocyanins and non-anthocyanin phenolics from blueberries with widely divergent profiles and biological activies

A sensitive and straightforward LC-IT-TOF-MS method was validated for the profiling and simultaneous quantification of anthocyanins, flavan-3-ols, flavonols, phenolic acids, and resveratrol in blueberry genotypes with fruit color ranging from deep purple (Vaccinium angustifolium) to various shades of pink (crosses of V. corymbosum, V. darrowii, and V. ashei). Standard calibration curves were linear for all analytes with correlation coefficients >0.99. The relative standard deviation for intra- and inter-day precision was lower than 10%. The method allowed an easy and selective identification and quantification of phenolics in blueberries with divergent profiles. The in vitro antioxidant assay results were strongly correlated with total phenolics and total anthocyanin content. Lowbush blueberry extracts (50 μg/mL) reduced ROS and NO production, and inhibited the transcription of the proinflammatory cytokines IL-6β, COX2, iNOS, and IL-6 in the in vitro assays at much lower concentrations than pink fruited berries (250 μg/mL).

LT25, LT50, and LT75 floral bud cold hardiness determinations for a diverse selection of Vaccinium genotypes

Ehlenfeldt, M. K., Rowland, L. J., Ogden, E. L. and Vinyard, B. T. 2015. LT25, LT50, and LT75 floral bud cold hardiness determinations for a diverse selection of Vaccinium genotypes. Can. J. Plant Sci. 95: 491-494. Freeze-bath cold hardiness results were used to calculate LT25 and LT75 values (temperatures causing 25% and 75% lethality, respectively) for a diverse selection of Vaccinium genotypes which had been previously analyzed for LT50 values. Overall, LT25 and LT75 values paralleled the LT50 values. Across genotypes, the LT25 was approximately 1.7°C (3.1°F) higher than the LT50, and the LT75 approximately 1.6°C (2.9°F) lower than the LT50 for any given date.