Susceptibility to crown gall disease was tested in 14 clones of Rosa indica Lour. non L., nine clones of R. multiflora Thunberg, two clones of R. canina L., two clones of R. manettii Crivelli, and some additional rootstock cultivars. Plants were inoculated with virulent strains of Agrobacterium tumefaciens biovar 1 (Smith and Townsend) Conn., the cause of crown gall disease. The highly susceptible cultivar `Sonia' was used as a positive control. Although all the clones were susceptible to A. tumefaciens during replicated tests, we observed a great variability in the percentage of galled plants and in the size of the galls among the genotypes tested. Three clones had a proportion of galled plants significantly lower than the control and may be useful in a rootstock breeding program for increased tolerance to crown gall. We confirmed previous results showing a reduction of shoot growth in the galled plants.
-layer branch from the top to the bottom of the crown), the middle terminal bud (the terminal bud of the middle-layer branch of the crown), and lower terminal bud (the terminal bud of the bottom-layer branch of the crown). Samples were taken from four directions
Larvae of several insects injure and kill strawberry (Fragaria ×ananassa Duchesne) plants by burrowing into and hollowing out plant crowns. Occasionally, these infestations are serious enough to cause heavy economic losses to fruit producers and nursery plant growers. In 1997 in Beltsville, Md., we observed wilting and dying mature plants and unrooted runner plants in two experimental strawberry plantings. Injury by larvae was extensive; large cavities occurred in crowns, and the central pith tissues were removed from stolons and leaf petioles. Often, insect frass was seen at entrance holes. Larvae removed from hollowed-out parts of injured plants were identified as the European corn borer (Ostrinia nubilalis Hübner) in their fifth instar stage. Their presence in this instance also was associated with a cover crop of millet [Setaria italica (L.) P. Beauv., `German Strain R'] planted between the strawberry rows for weed suppression. This is the first published report of the European corn borer attacking strawberry. Although this insect may occur only sporadically in strawberry plantings, it may become important in the future. Growers and other professionals should become aware of this new strawberry pest and recognize that its management in strawberry will be different from management of other crown-boring insects.
Osha (Ligusticum porteri) is a Rocky Mountain native frequently used as a medicinal herb. It is currently harvested largely from the wild. Studies have been under way since 2001 to find ways to propagate and produce the plant. To potentially increase rooting success of crown cuttings of osha, two different rooting hormones were used, each at two concentrations. Treatments were controls, 2500 ppm, and 5000 ppm solutions each of indole-3-butyric acid (IBA) and α-naphthalene acetic acid (NAA). Cuttings were soaked in deionized water or treatment solutions for 2 min. After soaking cuttings were stuck in sterilized sand in 725-mL2 containers, one cutting per container. Containers were placed on a mist propagation bench at 21 °C in a completely randomized design under natural light and day lengths. Data taken were days to visible root and shoot, and presence or absence of root formation after 50 days. Results indicated only one of 70 cuttings (<1%) produced a shoot. Roots formed on 14% of control cuttings, 64% in 2500 ppm IBA, 86% in 5000 ppm IBA, 36% in 2500 ppm NAA, and 14% in 5000 ppm NAA. Days to rooting ranged from 14.9 (2500 ppm IBA) to 29.0 (5000 ppm NAA). Due to considerable variation in days to rooting, and the number of cuttings that did not root, analysis of variance showed no differences among treatments. Frequency analysis indicated differences among treatments in root presence or absence. The 2500 and 5000 ppm IBA treatments showed more root formation than the controls or either NAA treatment. This indicates IBA may enhance rooting of osha crown cuttings.
similar climate and soil conditions. The mutant was then increasingly propagated, and yellow fruits were sold at first under the name ‘Huanxing’ in 2003. Subsequent evaluation showed that this selection was stable and renamed ‘Crown’ in accordance with the
Crown gall is an important disease of many fruit and nut crops, but little is known about sources of resistance. We screened germplasm from Prunus armeniaca L., P. angustifolia Marsh., P. argentia L., P. avium L., P. besseyi Bailey, P. bokhariensis Schneid., P. brigantica L., P. cerasifera Ehrh., P. cerasus L., P. dulcis (Mill.) D.A. Webb, P. fruiticosa Pall., P. hortulana Bailey, P. insititia L., P. japonica Thunb., P. mahaleb L., P. persica (L.) Batsch, P. serotina Ehrh., P. simonii Carr., P. sogdiana L., and P. webbii (Spach) Vieh. When either main stems or lateral branches of seedlings were inoculated with strains K12 and C58 of Agrobacterium tumefaciens (Smith and Townsend) Conn., the incidence of resistance was less than 10% except in some accessions of P. mahaleb L. where up to 30% of the plants were resistant. Some resistant plants were identified in other species, with P. insititia L. being the most promising. Symptoms based on presence and size of galls should be allowed to develop for up to 90 days after inoculation to reduce the likelihood of misclassifying plants as resistant when they are slightly susceptible.
Abstract
Dipping asparagus crowns (Asparagus officinalis L.) in 1000 ppm (2-chloroethyl)phosphonic acid (ethephon) solutions before planting significantly increased the number and fresh weight of both shoots and roots in pot studies. Ethephon treatment did not affect time of emergence, height, diameter of the shoots and root length. Of the concentrations tested (0, 250, 500, 750 and 1000 ppm), the 1000 ppm was the most effective; 750 ppm was partially effective while 250 and 500 ppm were ineffective. Under field conditions, ethephon and/or the potassium salt of gibberellic acid (KGA3) at 1000 ppm, did not affect the time of emergence of shoots from crowns treated before planting. Ethephon was effective in increasing the number of shoots while KGA3 alone or in combination with ethephon was not. Both chemicals reduced stand. Increasing exposure from 15 to 60 minutes increased the effectiveness of ethephon at 1000 ppm on inducing shoot emergence.
Abstract
Two everbearing strawberry (Fragaria × ananassa Duch.) selections were sprayed with the morphactin chlorflurenol (methyl-2-chlor-9-hydroxyfluorene-9-carboxylate) at concentrations of 5 to 80 ppm. From 1.8 to 2.8 times more crowns developed in treated plants of clone 25P29 than in controls and 1.9 to 4.3 times more in clone 12R70. Growth was temporarily retarded at all concentrations. Flower numbers were reduced by high chlorflurenol rates.
The effect of crown diameter on the regrowth of `Earliglow' and `Honeoye' strawberry (Fragaria × ananassa Duch.) plants was evaluated following exposure to sub-freezing temperatures. Large-diameter (12-14 mm) crowns of both cultivars had greater leaf number and dry weight than medium (9-11 mm) and small (6-8 mm) diameter crowns when plants were grown in the greenhouse after the freezing test. Large diameter crowns of both cultivars and medium-diameter crowns of `Honeoye' plants produced greater root dry weight than those of small-diameter crowns. The number of days to bloom of the primary flower increased with exposure to lower temperatures only in the large-diameter crowns of `Earliglow'. However, in small-diameter crowns of `Honeoye', the time of bloom decreased with exposure to lower temperatures. The fruit weight of small- and large-diameter crowns of `Earliglow' plants decreased linearly with exposure to lower temperatures. `Honeoye' plants subjected to -7C and unfrozen control plants had similar fruit weight.
Short productive lifespan is a major problem with asparagus (Asparagus officinalis L.), whether harvested in the spring or forced in late summer in coastal South Carolina. A modification of the Taiwanese system of mother stalk (MS) culture might enhance asparagus longevity and yield. The objective of this research was to determine if modified MS culture improved plant survival and yields in spring or summer-forced harvests compared with conventional spring clear-cut (CC) harvesting or with nonconventional summer-forced CC harvesting. `Jersey Giant' asparagus was harvested for 3 years (1994-96) using the following harvest systems: 1) spring CC (normal emergence in February in this location); 2) spring MS followed by summer MS (mow fern down on 1 Aug. and establish new mothers); 3) spring MS only; 4) summer CC only (mow fern on 1 Aug. and harvest); and 5) summer MS only. All systems were harvested for ≈7 weeks. All MS plots produced 40 mother stalks per 12-m row length each year before harvesting began. All mother stalks were trellised and tied to prevent lodging. Three-year total yields (kg·ha-1) and stand reduction (%) for nonharvested controls, spring CC harvesting, spring MS culture, spring MS combined with summer MS, summer CC, and summer MS were: 0 and 54%, 1621 and 96%, 779 and 99%, 1949 and 86%, 4001 and 58%, 3945 and 58%, respectively. All spring harvesting systems failed because by midsummer, aged fern, harvest pressures, and, apparently, higher rates of crown respiration reduced crown carbohydrate reserves. Yearly repetition of these stresses ultimately killed the spring-harvested plants. The MS culture did not ameliorate stand loss by significantly increasing carbohydrate reserves. Yields of summer-forced asparagus were consistently acceptable because aged ferns were removed at about the time they apparently became inefficient photosynthetically. After termination of the summer harvest season and with recovery in the following spring, ample carbohydrates were produced well before summer forcing began again in August the following year. Therefore, plant longevity was better sustained by summer forcing than by traditional spring harvesting.