There has been an historic interest in blackberries (Rubus spp.) among small fruit researchers; however, the number of research reports written on blackberries during the past 50 years has been relatively low. This workshop on blackberries was developed to fill a 50-year literature gap which became evident following a thorough search of the literature. Its genesis began when I was assigned to develop and teach a course in small fruits and viticulture at the Univ. of Illinois in Fall 1981. I wrote to many individuals to obtain up-to-date reprints, handouts, and bulletins on the various small fruit for my class. A large number of references on strawberries, grape, and blueberries was found, but there were very few recent publications on blackberries. Specific technical information on particular aspects of blackberry breeding and culture was found, but these articles often were not suitable for teaching purposes. Many papers on blackberries were published in the 1920s and 1930s. Recent information was scarce. I spoke with several small fruit specialists across the United States and discussed this problem with them. Eventually we agreed that the topic of blackberry production, breeding, propagation, and diseases should be examined in light of new information. This workshop was designed on the basis of these discussions.
‘Velvet Rose’ is a high polyploid, tissue culture-derived line (calliclone) from ‘Rober's Lemon Rose’, a scented geranium (Pelargonium graveolens L’Heritier ex. Alton) released for its sturdy plant type, general attractiveness, and vigor.
Phyllotaxy (the arrangement of leaves on the stem) in scented geranium is typically 2/5, i.e., in order to reach a leaf directly above another, it is necessary to maneuver 2 complete turns around the stem and pass 5 other leaves. We have observed variable phyllotaxy of certain clones of Pelargonium. For instance, in ‘Rober’s Lemon Rose’ (RLR) (Pelargonium graveolens L’Heritier ex. Ait on) nearly all plants change their phyllotaxy from 2/5 to 1/2 (Fig. 1, 2) (3) on either the main axis or lateral shoots. Most plants show: a) a region of 2/5 (usually the oldest growth near the base of the plant), b) a region of 1/2 (the newest growth), and c) a variable (1/2 + 2/5) region between these two (Table 1). The 2/5 phyllotaxy is associated with vegetative growth, while the 1/2 or 1/2 + 2/5 phyllotaxy is associated with flowering. The phyllotaxy switch was reversible. Lateral buds developing within a phyllotactic region could segregate all 3 patterns (Table 1).
Rubus laciniatus Willd. `Thornless Evergreen' (TE) is a chimeral blackberry with a thornless epidermis that overlies a genetically thorny interior. Most canes of TE produce leaves with 5 finely cut (lacinate) leaflets. Occasionally, canes appear which produce leaves with entire leaflets. Genetically pure thornless plants were regenerated from epidermal cells of chimeral TE with lacinate leaves. These regenerants exhibited somaclonal variation for growth habit, degree of thornlessness, and fruitfulness. All had lacinate leaves. When moved to the field, some of these regenerants produced canes with entire leaflets.
To examine the stability of the entire leaflet characteristic, plants were regenerated from lacinate leaves and entire leaves of both dwarf and normal pure thornless TE regenerants. Regenerants were rooted, moved to soil, and grown in the greenhouse for observation. Stability of this characteristic will be discussed.
To isolate unique fruit colors and look for somaclonal variation among regenerants, a regeneration protocol was established for various cultivars of striped apples (`Mailing 26', `Mutsu', `Regal Gala', `Summerland Red', and `Fuji'). Leaves were harvested from in m-grown plants, transferred to regeneration media [MS + NAA (5.4 μM) + TDZ (3 μM)], stored in the dark for 3 to 4 weeks, then moved to controlled light conditions, where adventitious shoot regeneration was observed. Developing shoots were transferred to proliferation medium and screened for their red or green phenotype by placing them on MS media containing various concentrations of sucrose (30, 45, 60, 75 and 90 g\L) and BA (0, 2.5, 5, 7.5, 10, 12.5 and 15 μM). Some of the regenerated apple shoots exhibited red color soon after being taken from the dark treatment. Others were less distinct, with colors ranging from dull green to a green-pink mixture. The red and green shoots are now being rooted and will be transferred to the field, where they will be grown to maturity.
Adventitious shoots were regenerated from apple (`Wijcik', `McIntosh', `Macspur', `M-26' and `Mutsu') by excising leaves from in vitro-grown shoots, cutting them into three sections, and plating them onto regeneration media. Cultures were kept in the dark for 1 to 4 weeks and then moved to light for further shoot development. MS medium supplemented with thiadiazuron (2-3 μM) and napthaleneacetic acid (5 μM) produced the highest number of shoots per leaf segment. `Wijcik' and `M-26' regenerated best from big leaves, whereas `McIntosh' and `Macspur' regenerated best from small leaves. Shoot formation was enhanced by 3 to 4 weeks of dark treatment and by placing the leaf on medium with its abaxial surface uppermost. The cut surface of leaf segments produced the most regeneration sites. In vitro adventitious shoots were transferred to various concentrations of BA (5, 10, 15, 20, 25 and 30 μM to screen them for BA tolerance and to predict their adult growth habit. These shoots will be rooted and transferred to greenhouse and field conditions for long-term evaluations.
The occurrence of chimeras, which are often unstable, limits the use of mutants in fruit tree improvement. Several types of spontaneous pear (Pyrus communis L.) chimeras have been described: variegated mutants with a chlorophyll deficiency, red mutants, and cytochimeras. Those that have been studied have proved to be periclinal chimeras, the mutation being present in either the L I, L II, or L III histogenic layer. Two methods have been used to separate these chimeras into pure types: 1) irradiation, which produces homogeneous shoots with L II or L III phenotype and a few new chimeral rearrangements; and 2) root cuttings followed by adventitious shoot regeneration, which produce only pure types, most of them with the L III phenotype. Both methods are time- and space-consuming. In vitro adventitious regeneration is suggested as a new technique to separate pear chimeras into pure types, or to be integrated in a mutagenesis program.
The first occurrence of fire blight on thornless blackberries (Rubus spp.) was reported in Illinois in 1976 (7, 8). Infections appeared either at the cane tip and proceeded basipetally, at axillary buds, causing cane girdling, or on flower/fruit clusters. Diseased portions of the canes were necrotic, purplish-black, and the tips were curved. Lesions were characteristically water-soaked and produced abundant bacterial ooze. Infected fruits did not develop to maturity, became brown, dried, very hard, and remained attached to the fruit pedicel. Frequently entire fruit clusters were infected but generally 1 or 2 fruits in each cluster escaped (Fig. 1). Mummified berries were commonly present on the 4 commercial cultivars (‘Thornfree’, ‘Dirksen Thornless’, ‘Black Satin’, and ‘Smooth-stem’) as well as several unnamed selections of similar genetic background to these cultivars. One seedling selection (SIUS 68-6-15) exhibited about 65% fruit infection. A bacterium was isolated from these fruits and from infected stems. The organism was morphologically and physiologically identical to, but pathogenically different from Erwinia amylovora (Burr.) Winslow et al. isolates from apple and pear.
The objective of this research was to induce vitrification in onion (Allium cepa L. cv. `White Ebeneezer'); then use this information to make suggestions on how to avoid vitrification of micropropagated plants. There were no differences in vitrification percentage when shoot tip explants were isolated, sterilized and placed on MS medium (8 g.L-1 agar) supplemented with 0.16 uM NAA and varying (0.0 to 70.0 uM) levels of BA. When agar was replaced by gelrite (MS medium with 4.4 uM BA and 0.16 uM NAA), vitrification increased when gelrite concentrations decreased from 2.0 to 1.0 g.L-1. More vitrification occurred when shoot tips were supported on a synthetic cosmetic puff in liquid medium or when agar was reduced to 4.0 g.L-1 than when supported on a cosmetic puff in 8 g.L-1 agar or on 8 g.L-1 agar alone.