Abstract
Ficus benjamina L. and F. stricta Miguel. were exposed to various concentrations of ethylene gas and ethephon to determine their sensitivity to defoliation. F. stricta was more sensitive to ethephon, whereas F. benjamina was more sensitive to ethylene gas. Plants growing in medium exposed to ethylene gas depleted ethylene from the ambient atmosphere. Double-autoclaving the peat : perlite growing medium prevented ethylene depletion, indicating soil microbes as the source of depletion. Bacterial isolates from the medium depleted ethylene in vitro; fungal isolates did not deplete ethylene. The eight species of bacteria isolated into pure culture depleted 9% to 46% of the ethylene from the flask atmosphere over 5 days, with two Enterobacter spp. and one Pseudomonas sp. being the most effective depleters. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).
Use of biological amendments in vegetable transplant production may affect plant development. Rhizosphere bacteria can alter conditions in the root zone and affect plant growth even if root tissue is not colonized. Arbuscular mycorrhizae (AM) affect plant development through symbiotic relations. Abiotic factors may mediate effects of biotic amendments. Organically certified potting medium was inoculated with a mix of Sinorhizobium sp. bacteria or a mix of AM fungi. Controls consisted of no amendment. Bell pepper, Capsicum annuum L., cv. Jupiter, seed were sown in the medium and irrigated either twice a day for 3 minutes per application or three times a day for 2 minutes per application. Seedlings were treated with 8, 16, 24, or 32 mL·L–1 of an organically certified liquid fertilizer beginning 3 weeks after sowing. Use of bacteria improved plant height and dry weight. Interactions of bacteria and fertilizer rate or irrigation regime affected plant height or dry weight. When irrigated twice a day, plants were tallest when provided 16 mL·L–1 fertilizer, and heaviest when provided 24 mL·L–1 fertilizer. When irrigated three times a day, plants were taller at the lower rates of fertilizer and heaviest at the highest rate of fertilizer. Use of AM had little effect on plant height and dry weight. Most of the responses when AM was the amendment were the result of fertilizer rate and irrigation regime. When irrigated twice a day, AM-treated plants were tallest and heaviest when provided at least 24 mL·L–1 fertilizer. Regardless of biological amendment, plant heights were correlated with plant dry weights over fertilizer rates and irrigation regime. Use of Sinorhizobium sp. appeared to provide a benefit to the development of bell pepper transplants.
Abstract
The effects of high (105 to 107 colony-forming units/g) and low populations of ice nucleation-active (INA) Pseudomonas syringae, strain B301D, on the ice nucleation temperatures and the amount of frost injury were determined for ‘Redhaven’ peach [Prunus persica (L.) Batsch.] and ‘Bing’ sweet cherry [Prunus avium (L.)] flower buds. The experiments were conducted from bud swell in early spring through the small, green fruit stages of development on INA bacteria-inoculated and -noninoculated flower buds that were either excised or attached to 10-cm segments of woody stem tissue. Shoots were immersed one minute in an INA bacterial suspension or sterile buffer 4 hours prior to freeze-testing. Excised-noninoculated buds supercooled to near −4°C before the first exotherm was determined, whereas inoculated buds attached to the stem supercooled only to −2.5°. Ice nucleation temperatures were about −3.0° for excised-inoculated and attached-noninoculated flower buds. The stem tissue contained a nonbacterial source of ice nucleation, active at temperatures similar to INA bacteria, that limited supercooling in the floral organs. While the ice-nucleation temperatures did not change with respect to bud development, the susceptibility of the floral organs to frost injury did change. Before the emergence of the petal tips through the calyx (frost-tolerant phase), the percentage of injury was reduced at higher ice nucleation temperatures, whether induced by stem tissue or inoculation with INA bacteria. Temperatures of −8 to −10° were required to give about 50% injury during this frost-tolerant phase compared with −3 to −4° in the later, frost-sensitive phase. Within a week of petal tip emergence from the calyx, the direct relationship between ice nucleation temperature and frost injury reversed, and the percentage of injury was inversely proportional to supercooling in flower buds. The flowers and fruit were injured by ice formation during the frost-sensitive phase regardless of whether ice was induced by INA bacteria or woody stem tissue.
A pawpaw (Asimina triloba) regional variety trial (PRVT) was established at the U.S. Department of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository (NCGR), Corvallis, Ore., in Fall 1995. This orchard was a replicated planting of 28 commercially available varieties or advanced selections from the PawPaw Foundation (PPF; Frankfort, Ky.), with eight replicate trees of each selection grafted onto seedling rootstocks and planted in a randomized block design. Two years after planting, 32 trees had either failed to establish or had died after an initial healthy start. By July 1999, 25% of grafted trees had died due to a vascular wilt-like disease, and 2 years later mortality exceeded 50%. Grafted selections with the lowest symptom severity include 1-7-2, 2-54, 7-90, 8-58, 9-58, `Mitchell', `PA-Golden #1', `Taylor' and `Wilson'. Seedling guard trees were unaffected until July 2000, when six guard trees of 76 died and 10 more were declining. By July 2001, 14 guard trees were dead. No fungi were consistently isolated from declining trees. A number of bacteria were isolated from infected trees, but no specific pathogen has been confirmed as the causal agent. Polymerase chain reaction (PCR) tests for phytoplasmas and for the bacterium Xylella fastidiosa were also negative. Research is ongoing to determine if a bacterial pathogen was the cause of the pawpaw decline in the Oregon PRVT.
Abstract
Two methods of removing bacteria from hydroponic nutrient solution [ultraviolet (UV) radiation and submicronic filter] were evaluated for efficiency and for their effects on lettuce (Lactuca sativa L.) production. Both methods were effective in removing bacteria; but, at high intensity, the ultraviolet sterilizer significantly inhibited the production of plants grown in the treated solution. Bacterial removal by lower intensity UV or a submicronic filter seemed to promote plant growth slightly, but showed no consistent, statistically significant effect.
Abstract
Rickettsia-like bacteria (RLB) are the presumptive cause of phony peach disease and are most numerous in peach (Prunus persica (L.) Batsch) roots. Of apparently healthy peach trees in a heavily infected orchard, 54% had RLB in root samples evaluated by 400 × phase contrast microscopy. Removing all peach trees with visible symptoms of phony peach disease would minimize the number of trees in the orchard infected with RLB. Of trees visibly infected with phony peach disease, 8% had root samples free of RLB on both sampling dates. Leaf concentrations of Mg and B varied significantly (P < 0.7%) with RLB levels in peach roots on 3 of 4 sampling dates. No element tested (P = 5%) separated roots free of RLB on two sampling dates from roots averaging 1 to 9 RLB per microscope field on one date and free of RLB on another date. RLB in peach roots preceded development of visible symptoms of phony peach and changes in leaf elemental concentrations. Soil analysis did not identify RLB infected tree roots (P = 5%).
There is very little information on the interaction of wine grape microflora with fungicides used to control grape diseases. The objective of this study was to determine how fungicides used in a standard grape pest management program and an experimental clay being developed for control of powdery mildew affect grape microflora. Grape leaves and fruit were surveyed for bacteria, fungi and yeast six times over the growing season in 2000 after treatment with clay or fungicides. In 2001 only clay was studied for control of powdery mildew in `Chancellor' grapes. The total number of propagules present on untreated leaf and fruit tissue were 76% bacteria, 14% yeast, and 9% fungi. Fungicides used for grape disease control significantly reduced epiphytic fungi (P < 0.0001), bacteria (P = 0.03), and yeast (P = 0.0001) on grape berries and epiphytic fungi (P < 0.0001), and yeast (P = 0.03) on leaves. The clay treatment had no detectable effect on grape microflora because no significant differences were recorded between clay or untreated grape berries or leaves on any of the sampling dates. Over the growing season the fungicide spray program reduced incidence and severity of powdery mildew better than clay. Clay controlled powdery mildew on `Chancellor' fruit in 2000 and 2001.
, 0.81 mg·kg −1 , 0.26 mg·kg −1 ; 1.33 g·cm −3 ; 28.6% and 16.9%, and 2.28%; and 1.44 g·kg −1 , respectively. Available water holding capacity of the soil is 121.3 mm in the 0.90 m soil profile. Experimental design and bacteria applications to
Amendment of soil with microorganisms during the growth cycle of one crop may affect development of succeeding crops. Species of Rhizobium bacteria or abuscular-mycorrhizal fungi were added alone to, or in combination with, potting soil in pots in a greenhouse. Controls were no amendments. Seed of peanut (Arachis hypogaea L.) were planted and two levels of a combination NPK fertilizer, the recommended and one-fourth the recommended rate, were applied. After harvest of peanut and remoistening of soil, seed of the bell pepper (Capsicum annuum L.) or navy bean (Phaseolus vulgaris L.) were sown into the same planting medium in pots without additional inoculation with microbes. Dry weights of above-ground vegetative and edible portions of crops were determined. Inoculum type only affected peanut top and total dry weights. The recommended fertilizer level did not affect peanut yield but did cause improvement in bell pepper and navy bean yield over that of the deficient fertilizer rate. In field experiments, peanut was planted into soil receiving Rhizobium spp. bacteria, or arbuscular-mycorrhizal fungi alone or in combination. Controls consisted of no amendment. Only the recommended fertilizer rate was used. In the next 2 years, bell pepper or navy bean were established in plots without use of additional microbial amendment. Yields and nutrient contents of crops were determined. Type of inoculum did not affect yield or nutrient content in any crop. Bell pepper marketable yield was unaffected by year, and navy bean seed yield was higher in 2004 than in 2005. In both years, navy bean yields were below U.S. averages. Concentrations of most nutrients in edible portions of bell pepper and navy bean were lower in 2004 than in 2005. Results of the field trials were generally similar to those of greenhouse studies. Use of inocula did not provide substantial benefits to yield or nutrient content of peanut or vegetable crops that followed.
chlorogenic acid can increase drastically when plants are attacked by viruses, bacteria, fungi ( Farkas and Kiraly, 1962 ; Frey-Wyssling and Babler, 1957 ; Kuć et al., 1956 ) nematodes, insects ( Dowd and Vega, 1996 ), or in response to various nonbiotic