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  • Author or Editor: Michele R. Warmund x
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Studies were conducted to characterize altered tissues of larvae-infested buds and stem and leaf galls induced by Dryocosmus kuriphilus Yasumatsu on Chinese chestnut trees (Castanea mollissima Blume) and to describe gall inhabitants. Bud and gall samples were collected from chestnut trees growing in Mantua, OH, on 2 Mar. and 3 May 2012, respectively, and prepared for microscopy. Uni- and multilocular larval chambers containing one D. kuriphilus larva per chamber were observed in buds and stem galls. Evidence of insect-modified Castanea cells was present as a two-layer zone of hypertrophied plant cells adjacent to the larval chambers before budbreak on 2 Mar. By 3 May, stem and leaf galls were in the growth and differentiation stage of development. Within galls, torn cell walls and disorganized organelles were visible in the protoplasm of cells surrounding ovoid-shaped larval chambers. A continuous layer of nutritive cells with large nuclei and nucleoli, abundant lipid bodies and mitochondria, and fragmented vacuoles was contiguous to larval chambers. At the outermost region of the nutritive tissue, cells had recently divided. Larger vacuolated cells, with slightly thickened walls, were observed surrounding recently divided cells. Thin-walled parenchyma cells in the chestnut gall cortex had large vacuoles with fewer organelles than those of the nutritive layer. Vascular tissue within the gall was connected with that of the plant host tissue outside the gall. In some chestnut galls, a single parasitoid larva was found attached to a D. kuriphilus larva. Each parasitoid larva had six pairs of setae on its head capsule, a pair of clypeal setae, a notched labrum, a semicircular lobed labium, 13 post-cephalic body segments, and rows of long, erect setae on all body segments.

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Chinese chestnut (Castanea mollissima Blume) is an exotic species that has potential as a niche crop. As a nut crop, it is relatively precocious in its bearing habit and has resistance to chestnut blight, tolerance to low winter temperatures, and relatively few pests. Current prices for fresh chestnuts are as much as $14/kg. Most U.S. chestnut growers (64%) have small orchards (less than 4 ha) and have been producing this crop for less than 10 years. Commercial chestnut production is low (≈680,000 kg) in the United States, but it is a relatively new industry in the central region. Limitations to growing this crop include a shortage of grafted trees, high tree costs, low yield efficiency, and high labor costs resulting from limited large-scale harvest equipment in the United States. However, results of ongoing research using cultivars on dwarfing rootstocks, thinning of secondary (2°) flowers, and improved tree nutrition will likely enhance profitability of production. In a 2003 Missouri survey, 67% of those interviewed had never consumed Chinese chestnuts but associated chestnut roasting with holidays. Chinese chestnuts provide health benefits. including a source of dietary fiber, a significant amount of vitamin C, no cholesterol, and are gluten-free.

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`Earliglow' strawberry (Fragaria × ananassa Duch.) plants were frozen to -5C to examine the distribution of ice in the crowns. Anatomical studies were also performed to characterize tissue growth in a greenhouse at 4, 8, and 16 weeks after freezing to -5C. Ice masses observed in fresh crown tissue corresponded to the presence of extracellular tissue voids in specimens fixed for scanning electron microscopy (SEM). Voids were present near the peduncle and adjacent to the vascular system in crown tissue. After plants were grown in the greenhouse, cell division and enlargement were observed near the voids in crowns subjected to -5C. By 15 weeks after freezing, a few small extracellular voids remained in the crowns.

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The time of rest completion of `Apache', `Arapaho', `Chickasaw', `Darrow', `Kiowa', `Navaho', and `Shawnee' blackberry (Rubus subgenus Rubus Watson) buds was compared and various models for estimating chilling were evaluated. `Kiowa' and `Arapaho' buds had the shortest rest periods, while those for `Shawnee', `Navaho', and `Chickasaw' buds were intermediate. `Apache' and `Darrow' buds had the longest rest periods. The model that accounted for the variation in percent budbreak among cultivars and temperatures during two dormant periods had the following two components: 1) a chilling inception temperature of –2.2 °C and 2) weighted chilling hours that accumulated after the chilling inception temperature. The chilling hours in this model were weighted as follows: 0 to 9.1 °C = 1; 9.2 to 12.4 °C = 0.5; 12.5 to 15.9 °C = 0; 16 to 18 °C = –0.5; >18 °C = –1. This study also elucidated that a blackberry model with a chilling inception temperature of –2.2 °C estimated chilling more accurately than one with chilling inception just after the maximum negative accumulation of chill units as used in the Utah chilling model. Also, temperatures between 0 and 2.4 °C must be weighted more heavily in a blackberry model than in the Utah peach model to accurately estimate chilling and rest completion.

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Experiments were conducted to determine the temperatures at which different densities of INA bacteria incite ice crystallization on `Totem' strawberry flowers and to determine if there is a relationship between densities of INA bacteria on strawberry flowers and floral injury. Primary flowers were inoculated with Pseudomonas syringae at 106 cells/ml buffer, incubated at 25°C day/10°C night and 100% RH for 48 h, and exposed to –2.0°C. No ice nucleation occurred on these inoculated flowers and all of the flowers survived. However, when inoculated flowers were subjected to lower temperatures, ice nucleation occurred at –2.2°C and few of the flowers survived. In contrast, ice crystals formed on the surface of most non-inoculated flowers at –2.8°C and 21% of the flowers survived exposure to –3.5°C. When INA bacterial densities were ≈105 colony forming units/g dry wt, floral injury occurred at a warmer temperature than to flowers that had lower bacterial densities.

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Inflorescences of `Earliglow' and `Honeoye' strawberry (Fragaria ×ananassa Duch.) plants were subjected to controlled freezing tests to determine the cold tolerance of styles, anthers, and receptacles of individual flowers at various stages of development. Flowers of both cultivars tended to deacclimate as the stages of development progressed. Styles and receptacles generally exhibited injury at higher temperatures than anthers. The greatest deacclimation of styles and receptacles of primary flowers occurred at earlier developmental stages of `Honeoye' than of `Earliglow'. However, at the sixth stage of development, the critical temperature for receptacle injury in primary and secondary fruit was -3C for both cultivars.

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Eastern black walnuts (Juglans nigra L.) were collected weekly in September and October to identify a method to determine the optimal harvest date and to develop a quantifiable color classification system for kernels. Husk hardness, measured by a durometer, decreased over a 5-week period. During the collection periods, the greatest percent kernel for ‘Emma K’, ‘Kwik Krop’, and ‘Sparrow’ was recorded when durometer values (i.e., force measurements) of husks were 5.2, 5.5, and 3.4 N, respectively. Husk softening was also detected using the denting method, but the perception of denting did not consistently correspond with a specific husk hardness value. Of the three cultivars, ‘Kwik Krop’ kernels were the most difficult to visually sort into light, medium, and dark colors. Kernel LCH sum (L* + chroma + hue angle values), measured by a handheld spectrophotometer, provided a reliable color classification for all black walnut cultivars in which light kernels had LCH sums ≥150, medium kernels had sums of 149 to 126, and dark kernels had values ≤125.

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Cryoprotectants were applied at labeled rates to primary flowers of `Honeoye' strawberry (Fragaria × ananassa Duch.) plants at full bloom to determine their effects on the floral organs. Frostgard at 50 ml/liter or KDL at 22 ml/liter injured pistils and resulted in misshapened fruit. Floral buds that were closed when cryoprotectants were applied were uninjured. In other experiments, efficacies of cryoprotectants were determined after floral tissues of `Honeoye' strawberry plants were inoculated or not inoculated with the ice-nucleation-active (INA) bacteria, Pseudomonas syringae van Hall and subjected to sub-freezing temperatures. None of the products protected primary or secondary flowers against freezing injury regardless of the occurrence of INA bacteria. INA bacteria were not recovered from primary flowers of treated plants that were killed by low temperature exposure, indicating that non-bacterial nuclei may incite freezing in these tissues.

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Cane dieback and foliar necrosis caused by an unknown pathogen were observed in elderberry (Sambucus nigra subspecies) plantings in early Spring 2016. Studies were conducted to identify the causal organism and determine the effects of infection on vegetative growth and fruiting of selected elderberry cultivars under controlled conditions. A Heterophoma sp. was isolated from symptomatic ‘Ranch’ elderberry canes growing in a commercial planting in Missouri. In the subsequent 2017 experiments, all canes of ‘Bob Gordon’ plants inoculated with this Heterophoma isolate had reduced cane lengths, reduced numbers of leaves and leaflets, and failed to produce fruit. In a study using ‘Scotia’, none of the 32 inoculated canes had symptomatic tissue; but in a subsequent study, one of 16 inoculated canes had slight cane dieback, indicating a potential difference in cultivar susceptibility to the pathogen. In 2018, seven elderberry cultivars (‘Adams II’, ‘Bob Gordon’, ‘Marge’, ‘Ozark’, ‘Scotia’, ‘Wyldewood’, and ‘York’) were inoculated with the same Heterophoma isolate, which was subsequently reisolated from the boundary of symptomatic and asymptomatic tissue, thereby confirming pathogenicity of the fungus. The fungus was tentatively identified as H. novae-verbascicola (Aveskamp, Gruyter & Verkley) Q. Chen & L. Cai based on analysis of genomic DNA from the internal transcribed space (ITS) region. Only two of 16 ‘Scotia’ inoculated canes had cane dieback in 2018, whereas inoculated canes of all other cultivars developed symptoms. Cane and foliar growth of each inoculated cultivar was less than the associated noninoculated control at 14, 30, and 60 days after treatment (DAT). Among inoculated symptomatic plants, ‘Marge’ canes produced more vegetative growth than all other cultivars, and ‘Adams II’, ‘Ozark’, and ‘York’ canes generally produced the fewest number of leaves and leaflets at 60 DAT. Flowering was observed on canes of noninoculated control plants, but not on inoculated symptomatic canes by 60 DAT. Thus, the newly reported cane dieback disease of elderberry, caused by Heterophoma sp., adversely affected plant growth and fruiting of Sambucus nigra subspecies. However, ‘Scotia’ elderberry plants were less susceptible to the fungal infection than other cultivars, indicating that it may be possible to use ‘Scotia’ to develop new elderberry cultivars with improved resistance to infection by Heterophoma.

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“Ambers” is a term used to describe poorly filled, shriveled eastern black walnut (Juglans nigra L.) kernels with a dark brown or black-colored pellicle that are unmarketable. Studies were conducted to determine the incidence of ambered black walnut kernels and to ascertain when symptoms were apparent in specific tissues. The occurrence of ambered kernels was evaluated in fruit harvested from mature ‘Football’ trees growing at three sites within a commercial black walnut orchard in 2008 to 2010. Mature walnut fruit sampled from trees at Site 2 had greater odds for ambered kernels than those on trees at two other sites within the same orchard with 27% of the walnuts sampled exhibiting symptoms when examined in October. Also, black walnut fruit in 2010 had more ambered kernels than those examined in Oct. 2008 or 2009. Cropload, soil type, ambient temperatures, or precipitation was not apparently associated with a high incidence of ambered kernels. When black walnut fruit from trees at Site 2 were examined from 25 June to 6 Oct. 2011, embryos were visible in 50% of the fruit without discoloration on the first date. Stenospermocarpy (e.g., aborted or rudimentary embryos after fertilization) was observed in fruit with discolored or ambered kernels as early as 7 July. Stenospermocarpic fruit with ambered kernels had shorter embryo axis lengths (root apex to shoot apex) than fruit with non-ambered kernels on 7 July and at successive sampling dates. Cotyledon widths of ambered kernels in stenospermocarpic fruit were narrower than those of non-ambered kernels on 21 July, but symptomatic cotyledons continued to enlarge until 15 Sept. All fruit enlarged during the growing season and nut diameters varied by only 3.4 mm at harvest. Thus, visible embryo degeneration, which was associated with ambered kernels in black walnut fruit, was detected in early July when shell hardening occurs and kernel tissues are enlarging.

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