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Mark K. Ehlenfeldt and Matthew Kramer

Rabbiteye blueberry hybrids that the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS) program has bred for northern adaptation are combinations of 6x V. ashei Reade, 6x V. constablaei Gray, 4x V. corymbosum L., and 2x V. darrowii Camp germplasm at the hexaploid level and are generally composed of 50% or greater V. ashei (rabbiteye) germplasm. Four northern-adapted rabbiteye (NRE) selections (US 1043, US 1045, US 1056, US 1057), four rabbiteye standards (‘Brightwell’, ‘Climax’, ‘Tifblue’, ‘Woodard’), two rabbiteye × V. constablaei derivatives (‘Little Giant’, ‘Snowflake’), and two highbush standards (‘Duke’, ‘Bluecrop’) were pollinated under greenhouse conditions with either self-pollen or a multicultivar, bulk-pollen mixture (appropriate to ploidy level and species) to determine the relative requirements for cross-pollination among NRE selections. Fruit set, berry weight, and seed set were subsequently evaluated. The results suggest that NRE selections, in general, exhibit cross-pollination needs intermediate to the parent types such that: rabbiteye > northern rabbiteye > highbush (i.e., rabbiteye has the lowest self-fertility and the greatest need for cross-pollination). Considerable variation existed among the NRE selections tested, which suggests that it might be possible to select clones with good levels of self-fertility, potentially equivalent to that of highbush blueberry.

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James J. Polashock and Matthew Kramer

Stem diseases of blueberry (Vaccinium spp.) can cause significant crop loss as well as loss of entire bushes. Stem diseases are also more difficult to control with fungicides than foliar or fruit diseases. A screening program was initiated to test blueberry cultivars for resistance to two pathogenic fungi: botryosphaeria stem blight and phomopsis twig blight. An attached stem assay was developed to compare the host response with both fungi. The relative resistance of 50 blueberry cultivars was assessed using stem lesion lengths, analyzed on a log scale, taken at 4 weeks postinoculation. For Botryosphaeria stem blight, mean lesion length ranged from about 10 mm in resistant cultivars to about 140 mm in susceptible cultivars. The half-high cultivars Northsky, Northblue, and Chippewa, and the lowbush cultivar Putte were among the most resistant. Phomopsis twig blight lesions ranged in mean length from about 18 to 98 mm. Similar to results for Botryosphaeria stem blight, resistance was limited to half-high (`Northsky' and `Chippewa') and lowbush (`Blomidon', `Chignecto', and `Cumberland') cultivars. Individual cultivars resistant to one pathogen were not necessarily resistant to the other; although, overall, the resistances were correlated. Approximate 95% confidence intervals were established for all cultivars to predict mean performance across years. The cultivars tested varied in resistance, but the largest single factor affecting lesion length was the fungal isolate used for inoculations. These data enable us to identify cultivars resistant to both diseases that can be used for planting in problem areas, as well as selection of parental material for breeding cultivars with improved resistance.

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Yonghong Guo, Matthew Kramer and Margaret Pooler

Ornamental flowering cherry trees are important landscape plants in the United States but are susceptible to several serious pests and disease problems. Cherry leaf spot, incited by the fungus Blumeriella jaapii, is characterized by defoliating susceptible trees in late summer, leading to weakening or even death of the tree. To identify resistant plants for use in landscape plantings and in our breeding program, we used a detached leaf assay to screen 69 diverse ornamental flowering cherry taxa for resistance to cherry leaf spot. We found clear differences in susceptibility among the accessions, with seven accessions developing essentially no symptoms at all. A variance decomposition showed that most of the variance (59%) occurred among accessions, indicating that genotype, even more than species, determined susceptibility. The detached leaf assay used in this study is an effective method for screening large numbers of plants for relative resistance to cherry leaf spot. These methods will be particularly useful to characterize germplasm and screen hybrids in breeding and selection programs.

Open access

Matthew H. Kramer, Ellen T. Paparozzi and Walter W. Stroup

We examined all articles in volume 139 and the first issue of volume 140 of the Journal of the American Society for Horticultural Science (JASHS) for statistical problems. Slightly fewer than half appeared to have problems. This is consistent with what has been found for other biological journals. Problems ranged from inappropriate analyses and statistical procedures to insufficient (or complete lack of) information on how the analyses were performed. A common problem arose from taking many measurements from the same plant, which leads to correlated test results, ignored when declaring significance at P = 0.05 for each test. In this case, experiment-wise error control is lacking. We believe that many of these problems could and should have been caught in the writing or review process; i.e., identifying them did not require an extensive statistics background. This suggests that authors and reviewers have not absorbed nor kept current with many of the statistical basics needed for understanding their own data, for conducting proper statistical analyses, and for communicating their results. For a variety of reasons, graduate training in statistics for horticulture majors appears inadequate; we suggest that researchers in this field actively seek out opportunities to improve and update their statistical knowledge throughout their careers and engage a statistician as a collaborator early when unfamiliar methods are needed to design or analyze a research study. In addition, the ASHS, which publishes three journals, should assist authors, reviewers, and editors by recognizing and supporting the need for continuing education in quantitative literacy.

Free access

Yonghong Guo, Richard T. Olsen, Matthew Kramer and Margaret Pooler

Two simple and rapid in vitro bioassays using detached stems were developed for evaluating the susceptibility of boxwood genotypes to the blight disease caused by Calonectria pseudonaviculata (Crous et al.) L. Lombard et al. Individual leaves were inoculated on detached stems or entire detached stems were sprayed to assess susceptibility. Both assay systems were optimized for inoculum concentration and disease rating time. The assay methods described here require minimal plant material and inoculum, especially the leaf inoculation assay, which uses as few as six leaves per stem and 500 spores per leaf for inoculation. The stem spray inoculation produced less variable results and was easier for quantifying susceptibility but required more inoculum than the leaf inoculation assay. No differences between the assays were found for the cultivars tested. The leaf inoculation assay is best used when limited plant material or inoculum is available; the spray inoculation of detached stems is suitable when larger plants are available.

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Orville C. Baldos, Joseph DeFrank, Matthew Kramer and Glenn S. Sakamoto

Tanglehead (Heteropogon contortus) is a drought- and fire-tolerant native Hawaiian grass that possesses seed dormancy on shedding. Although a dry after-ripening period is known to break dormancy, specific storage conditions to optimize this are not known. This study examined the effects of storage temperature and equilibrium relative humidity (eRH) on tanglehead seed dormancy loss and viability. Fresh seeds harvested in Mar. and Oct. 2011 were stored for 30 days in three eRH levels (12%, 50%, and 75%) and then incubated for 0, 1, 3, 6, 9, and 12 months at three temperatures [10, 20 (ambient in laboratory), and 30 °C]. The eRHs were maintained during incubation by sealing seeds in airtight packages. Seed germination and tetrazolium tests were conducted after each incubation period to determine dormancy loss and seed viability. Analysis of germination and seed viability data indicated a significant interaction among eRH, storage temperature, incubation period, and seed harvest month. Storage at 12% eRH and 30 °C for 12 months optimized dormancy loss of tanglehead seeds. Seeds remained viable in all eRH and temperature combinations except those stored at either 75% eRH and 20 °C or 75% eRH and 30 °C. In these treatment combinations, significant seed deterioration and loss of viability were recorded. Harvest time (i.e., harvest month) within the year also affected the rate of dormancy loss of seeds. March-harvested seeds achieved maximum dormancy loss 3 months earlier than seeds harvested in October.

Open access

Matthew H. Kramer, Ellen T. Paparozzi and Walter W. Stroup

We examined all articles in volume 139 and the first issue of volume 140 of the Journal of the American Society for Horticultural Science (JASHS) for statistical problems. Slightly fewer than half appeared to have problems. This is consistent with what has been found for other biological journals. Problems ranged from inappropriate analyses and statistical procedures to insufficient (or complete lack of) information on how the analyses were performed. A common problem arose from taking many measurements from the same plant, which leads to correlated test results, ignored when declaring significance at P = 0.05 for each test. In this case, experiment-wise error control is lacking. We believe that many of these problems could and should have been caught in the writing or review process; i.e., identifying them did not require an extensive statistics background. This suggests that authors and reviewers have not absorbed nor kept current with many of the statistical basics needed for understanding their own data, for conducting proper statistical analyses, and for communicating their results. For a variety of reasons, graduate training in statistics for horticulture majors appears inadequate; we suggest that researchers in this field actively seek out opportunities to improve and update their statistical knowledge throughout their careers and engage a statistician as a collaborator early when unfamiliar methods are needed to design or analyze a research study. In addition, the ASHS, which publishes three journals, should assist authors, reviewers, and editors by recognizing and supporting the need for continuing education in quantitative literacy.

Open access

Matthew H. Kramer, Ellen T. Paparozzi and Walter W. Stroup

We examined all articles in volume 139 and the first issue of volume 140 of the Journal of the American Society for Horticultural Science (JASHS) for statistical problems. Slightly fewer than half appeared to have problems. This is consistent with what has been found for other biological journals. Problems ranged from inappropriate analyses and statistical procedures to insufficient (or complete lack of) information on how the analyses were performed. A common problem arose from taking many measurements from the same plant, which leads to correlated test results, ignored when declaring significance at P = 0.05 for each test. In this case, experiment-wise error control is lacking. We believe that many of these problems could and should have been caught in the writing or review process; i.e., identifying them did not require an extensive statistics background. This suggests that authors and reviewers have not absorbed nor kept current with many of the statistical basics needed for understanding their own data, for conducting proper statistical analyses, and for communicating their results. For a variety of reasons, graduate training in statistics for horticulture majors appears inadequate; we suggest that researchers in this field actively seek out opportunities to improve and update their statistical knowledge throughout their careers and engage a statistician as a collaborator early when unfamiliar methods are needed to design or analyze a research study. In addition, the ASHS, which publishes three journals, should assist authors, reviewers, and editors by recognizing and supporting the need for continuing education in quantitative literacy.

Free access

Hongmei Ma, Richard Olsen, Margaret Pooler and Matthew Kramer

Flowering cherries belong to the genus Prunus, consisting primarily of species native to Asia. Despite the popularity of ornamental cherry trees in the landscape, most ornamental Prunus planted in the United States are derived from a limited genetic base of Japanese flowering cherry taxa. A diverse collection of ornamental Prunus germplasm is maintained at the U.S. National Arboretum as part of an ongoing flowering cherry improvement program, but the genetic backgrounds of many trees are unclear. We characterized this germplasm using five simple sequence repeat (SSR) primer pairs, including one chloroplast primer pair. These primers generated 140 unique alleles that were used to assess genetic relationships among species, hybrids, and cultivars in this collection. We found that these markers followed expected Mendelian inheritance from parents to progeny in controlled hybridizations. In general, species clustered according to published taxonomic groupings, including a distinct separation of the ornamental cherries (Prunus subgenus Cerasus section Pseudocerasus) from other subgenera. Individual accessions of several taxa did not cluster with other samples of the species, indicating possible misidentification or interspecific combinations. The resulting information will be useful in guiding decisions on breeding methodology and germplasm preservation.

Free access

James J. Polashock, Robert A. Saftner and Matthew Kramer

Fruit of highbush blueberry (Vaccinium corymbosum L.) produce antimicrobial volatiles, including trans-2-hexenal, that may confer resistance to anthracnose fruit rot, an important postharvest disease caused by Colletotrichum acutatum J.H. Simmonds. To investigate whether aromatic volatiles in highbush blueberry fruit are associated with postharvest fruit rot resistance, we compared volatiles emitted from whole fruit and extracts from fruit kept in air at 20 °C for 0 to 6 days postharvest from cultivars having a wide range of resistance to anthracnose. Antimicrobial volatiles detected included the aldehydes, trans-2-hexenal and hexanal; the monoterpenes, limonene, linalool, 8-hydroxylinalool, α-terpineol, and terpinyl acetate; and the sesquiterpenes, cadinene, caryophyllene, and α-farnesene. There were significant correlations between some detected volatiles and these differed in whole fruit and extracts. Hexanal (in fruit extracts), trans-2-hexenal, terpinyl acetate, and cadinene emissions increased in most cultivars when fruit were kept in air at 20 °C for various times postharvest. Volatile emissions from whole fruit and extracts varied widely among the cultivars with early ripening cultivars generally showing higher volatile emissions than later ripening cultivars. Although the cultivars tested differed in quantities, and in some cases, the types of volatiles produced, these differences were not related to pedigree (i.e., species composition) nor to known anthracnose resistance ratings. Except for the confounded emissions of terpinyl acetate and cadinene, more than 80% of the variation observed for each volatile was attributable to the cultivar (genetic), year (environmental), and cultivar–by-year interaction. The results suggest that, although antimicrobial aldehydes and terpenes emitted from fully ripe highbush blueberry fruit and extracts might be important flavor and aroma components, they do not significantly contribute to disease resistance against anthracnose fruit rot.