To study the causes of low germinability in dried blackberry seeds, seeds harvested from fresh `Thornless Evergreen' (TE) blackberry (Rubus laciniatus Willd.) were either air-dried (12, 24, 36, 48, 60, 72, 96, or 120 hours) or explanted directly onto growth-regulator-free medium after bleach disinfestation. Seeds were either cut in half before explanting or kept intact. None of the intact seeds germinated. Fewer of the halved seeds dried 12 hours or more germinated than control (fresh moist) seeds (42.7% and 54.5%, respectively). Germination decreased to <12% following >48 hours of air-drying. In a separate study, fresh seeds of TE and `Navaho' were either dried as described or held in sealed petri dishes on moist filter paper (moist treatment) for up to 60 hours. After 60 hours, germination of dried seeds of both cultivars had decreased significantly; there was no significant change in germination percentage for moist seeds. Since moist halved seeds germinated well and dried halved seeds did not, the inability of dried blackberry seeds to germinate is due to more factors than just the hard seedcoat typical of the genus.
M.A.R. Mian, R.M. Skirvin, M.A. Norton, and A.G. Otterbacher
M. R. Warmund, M. F. George, M. R. Ellersieck, and J. V. Slater
Experiments were performed on ‘Cherokee’ blackberry (Rubus sp.) floral buds and cane tissue collected from field plantings on 12 Jan. and 18 Feb. 1987 to determine the susceptibility of floral primordia, phloem, and xylem to freezing injury after exposure to 16C for 0, 4, 12, 24, or 48 hr. Before rest completion in January, floral primordia, phloem, and xylem subjected to 16C were hardier than those tissues tested in February when rest was completed. Floral primordia and cane tissues dehardened slowly with time at 16C before rest completion. After rest was completed, the rate of deacclimation of floral primordia and xylem increased. Some blackberry canes were subjected to two thawing episodes at 16C for 4 hr. In January, phloem and xylem of canes thawed twice were as hardy or hardier than those tissues in samples thawed once. Conversely, two thawing episodes in February resulted in greater xylem injury than a single episode, but two episodes did not affect the hardiness of the phloem. The number of thawing episodes did not affect floral bud hardiness at either sampling date.
Jessica M. Cortell and Bernadine C. Strik
In Spring 1993 and 1994, treatments of 0, 4, 8, and 12 floricanes per plant were established in a mature `Marion' planting. Primocanes were measured weekly for the number and length of primocanes and primocane branches. Maximum hardiness of primocanes was determined in Jan. 1994 and 1995 by controlled freezing. Yield components were measured in both the current and following season. Additional plants were harvested in summer and winter for dry-weight partitioning. Plants with no floricanes had an increased number and length of primocanes and branches than plants with floricanes in 1993, with similar trends in 1994. Primocane growth on plants without floricanes showed a 65% increase in primocane dry weight in 1993. However, in 1994, there were no significant differences among treatments. Primocane branch dry weight generally increased with decreasing floricane number. The relationship between primocane growth and the following season's yield components will be presented.
Gerald M. Sapers, Anita M. Burgher, Susan B. Jones, and John G. Phillips
Fruits from thornless blackberry (Rubus sp.) cultivars were compared to determine causes of variation in drip losses during thawing after frozen storage. Drip was similar in composition to juice obtained by pressing. Drip losses for different cultivars ranged between 1% and 30% in 1984; increased losses in 1983 were attributed to poor fruit condition (e.g., deterioration during postharvest holding). Drip losses were greater in riper samples but did not depend on fruit size. Drip losses were correlated with low insoluble pectin. Microscopic examination revealed an inverse relationship between the tendency to drip and the epidermal cell layer thickness.
D.J. Donnelly, F.E. Skelton, and J.E. Nelles
Foliar anatomical comparisons were made between in vitro-grown plantlets and greenhouse-grown plants of ‘Silvan’ blackberry (Rubus sp.) using scanning and light microscopy. Each apex and marginal serration of in vitro- and greenhouse-grown leaves had a terminal hydathode region composed of a scattered, primarily adaxial, group of sunken water pores. Water pores and stomata of plantlet leaves were open, while greenhouse-grown plant leaves had closed water pores and stomata or comparatively small apertures. Internally, the hydathodes of both cultured plantlets and greenhouse-grown plants were delimited by a bundle sheath that flanked the vascular tissues and extended to the epidermis. Between the vascular tissues and the epidermis were loosely arranged epithem cells. The hydathodes of plantlet leaves were simpler than those of greenhouse-grown plants, with fewer water pores and reduced epithem. Water loss from detached leaves of plantlets occurred through both leaf surfaces, although more water was lost from the abaxial surface. In contrast, foliar water loss from severed leaf blades of greenhouse-grown plants was primarily abaxial.
Michael E. Compton and John E. Preece
The effects of catechol, juglone, phloridzin, phloroglucinol, and tannic acid were tested on tobacco callus growth and on axillary shoot proliferation and rooting of blackberry. Juglone (500 μM) promoted tobacco (Nicotiana tabacum L. ‘McNair 944’) callus growth, whereas catechol and phloroglucinol (500 μM) increased adventitious shoot formation, but not callus growth. Tannic acid increased the frequency of vitreous shoots. No phenolic compounds stimulated axillary shoot proliferation in blackberry (Rubus sp. ‘Dirkson Thornless’), and phloroglucinol (1 mM) inhibited shoot elongation. Auxin increased rooting of blackberry shoots irrespective of the presence or absence of incorporated phenols. On shoots derived from proliferation media void of phenols, root number and percent rooting were greater if they were treated with the phenolic auxin P-ITB compared to IBA. In contrast, shoots originating from proliferation media containing phenols rooted the same with both auxins. Chemical names used: 1,2-benzenediol (catechol); 5-hydroxy-1,4-naphthalendedione (juglone); 1-[2-(β-D-glycopyranosloxy)-4,6-dihydroxyphenyl-3-[4-hydroxyphenyl)-1-propanone (phloridzin); 1,3,5-benzenetriol (phloroglucinol); 1H-indole-3-butanoic acid (IBA); N-(phenylmethyl)-1H-purin-6-amine (BA): phenyl indole-3-thiolobutyrate (P-ITB); (1α,2β,4aα,4bβ,10β)-2,4a,7-trihydroxy-1-methyl-8-methylenegibb-3-ene-1, 10-dicarboxylic acid 1,4a-Iactone (GA3).
Chad E. Finn, Brian M. Yorgey, Bernadine C. Strik, Robert R. Martin, and Michael Qian
Jose Lopez-Medina and James N. Moore
Jose Lopez-Medina, James N. Moore, and Kyung-S. Kim
Scanning electron microscopy (SEM) and light microscopy (LM) were used to study the transition of meristems from vegetative to floral phase in erect primocane-fruiting (PF) blackberries [Rubus (Tourn.) L. subgenus Rubus] developed at the Univ. of Arkansas. Dormant root cuttings of A-1836 and APF-13 blackberries were dug from the field and planted on 28 Dec. 1996 and 1 Mar. 1997 to produce plants for use in a greenhouse study. In a field study, terminal buds of field-grown A-1836, APF-13, NC194, and summer-fruiting `Arapaho' were sampled on 21 Mar 1997 (before shoot emergence from soil), and then weekly from 14 to 28 May 1997. Flower bud primordia were first observed at five and six nodes of growth in greenhouse-grown A-1836 and APF-13 plants, respectively, 35 to 42 days after root cuttings were planted (DAP). Under field conditions, floral primordia were not observed until 21 May when A-1836 and APF-13 had at least 20 nodes of growth; NC194 did not differentiate floral structures until 10 July. The developmental patterns of the vegetative apical meristem in the PF selections, both field- and greenhouse-grown plants, were similar to those of `Arapaho'. Opening of the terminal flower of the inflorescence occurred 32 to 35 days after floral initiation in APF-13, and 8 to 10 days later on A-1836. Field-grown NC194 bloomed in late August. The first fruits of greenhouse-grown APF-13 were harvested 120 DAP. These findings demonstrate that PF blackberries form flower buds after a short period of vegetative growth.