Search Results

You are looking at 21 - 30 of 755 items for :

Clear All

In 1993, ice-nucleation-active (INA) bacteria were isolated from `Redwing' red raspberries (Rubus idaeus L. var. idaeus) at five pigmentation stages. Fruit were also subjected to thermal analysis to determine the ice nucleation temperatures. INA bacteria were recovered from nearly all fruit samples, and the bacterial populations tended to decrease with greater red color development (i.e., fruit maturation). However, the ice nucleation temperature was not affected by the stage of fruit pigmentation. In 1994, INA bacterial densities were similar among fruit at the three pigmentation stages sampled. INA bacteria were recovered more often from the calyx rather than the drupe surface of these fruit. INA bacteria also were detected on pistils of some fruit. Red and pink fruit, which were nucleated with ice, had greater receptacle injury than mottled, yellow, or green fruit, but INA bacterial densities apparently were not related to injury. Thus, the injury response of fruit at different pigmentation (or development) stages indicated that nonbacterial ice nuclei may be involved in freezing injury of developing raspberries.

Free access

INA bacteria were isolated from primary flowers of `Totem' strawberry (Fragaria ×ananassa Duch.) plants that had been previously inoculated with strain Cit 7 of Pseudomonas syringae van Hall or noninoculated to determine their relationship to ice-nucleation temperature and floral injury. Mean ice-nucleation temperature of inoculated and noninoculated flowers was -2.2 and -2.8 °C, respectively. Primary flowers of noninoculated plants survived lower temperatures than those of inoculated plants. In another experiment, noninoculated plants were misted with sterile deionized water and incubated for 0, 12, 24, 36, or 48 hours at 25 °C day/10 °C night, and naturally occurring INA bacteria were isolated from primary flowers. INA bacterial densities increased exponentially with increasing incubation period. The critical wetness period for INA bacteria to establish a sufficient density to increase the likelihood of floral injury at -2.5 °C was 24 hours. Longer wetness periods resulted in higher INA bacterial densities but did not increase the floral mortality rate. Thermal analysis demonstrated that the ice nucleation temperature was associated with strawberry floral injury. Thus, low temperature survival of flowers was adversely affected by moisture for ≥24 h due to the presence of a sufficient density of INA bacteria to incite ice formation and floral injury.

Free access

Abstract

Epiphytic populations of ice nucleation active (INA) strains of Pseudomonas syringae van Hall of up to 106cells/g fresh weight were found on healthy tissues of commercially managed almond [Prunus dulcis (Mill.) D.A. Webb] orchards in California. Leaf bacteria accounted for over 99% of the ice nuclei active at temperatures higher than − 5°C on almond. Large, seasonal variations in populations of INA bacteria and ice nuclei on almond were observed, with maximum populations found shortly after full bloom. These populations were reduced from 10- to 100-fold by 3 weekly applications of bactericides starting at budbreak, or a single application at 10% bloom of a nonice nucleation active antagonistic bacterium isolated from an almond leaf surface. Applications of cupric hydroxide to dormant tissues and/or to growing tissue after budbreak were most effective at reducing populations of INA bacteria and ice nuclei on almond. Application of bacterial ice nucleation inhibitors did not influence populations of INA bacteria on almond shoots shortly after application, but reduced the numbers of ice nuclei active at −5° or warmer. Frost injury to detached almond spurs cooled to −3° was reduced by all treatments that reduced the numbers of bacterial ice nuclei on almond tissue.

Open Access

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.

Free access

The antibacterial activity of artificially grown sweetpotato [Ipomoea batatas (L.) Lam.] leaves was investigated against both gram positive and gram negative bacteria namely Escherichia coli (O157:H7), Bacillus and Ecolai using three different cultivars, which are developed to use as a leafy vegetables namely Simon-1, Kyushu-119 and Elegant Summer. The sweetpotato leaves were grown under different temperatures (20 °C, 25 °C, and 30 °C) and artificial shading (O%, 40% and 80%) conditions. There were some cultivar differences but the lyophilized leaf powder (100 mg) from all the cultivars in the Trypto Soya Broth cultivation medium (10 mL) strongly suppressed the growth of all the bacteria studied and its effect was detectable even after autoclave treatment. But the antibacterial extract of the leaves had no effect on the growth of five types of bifidobacterium useful for human health. The water extracted antibacterial fractions from all the cultivars were viscous and the color was brown. Furthermore, the leaves grown under moderate low temperature (20 °C) with 0% shading treatments strongly suppressed the bacterial growth as comported to other treatments, which was accompanied by significantly high accumulation of sugar and polyphenol contents in the leaves. The results also suggest that there were a strong relationship among bacterial growth and antioxidatative compounds in the sweetpotato leaves. Therefore, the antibacterial action of sweetpotato leaves may depend on their antioxidative compounds or/and pectin like materials. Thus, the practical use of sweetpotato leaves is expected to prevent bacteria caused food poisoning.

Free access

Biofumigation by volatiles of Muscodor albus Worapong, Strobel & W.M. Hess, an endophytic fungus, was investigated for the biological control of three postharvest fungi, Botrytis cinerea Pers., Penicillium expansum Link, and Sclerotinia sclerotiorum (Lib) de Bary, and three bacteria, Erwinia carotovora pv. carotovora (Jones) Bergey et al., Pseudomonas fluorescens Migula (isolate A7B), and Escherichia coli (strain K12). Bacteria and fungi on artificial media in petri dishes were exposed to volatiles produced by M. albus mycelium growing on rye seeds in sealed glass 4-L jars with or without air circulation for up to 48 hours. The amount of dry M. albus–rye seed culture varied from 0.25 to 1.25 g·L–1 of jar volume. Fan circulation of volatiles in jars increased efficacy and 0.25 g·L–1 with fan circulation was sufficient to kill or suppress all fungi and bacteria after 24 and 48 hours, respectively. Two major volatiles of M. albus, isobutyric acid (IBA) and 2-methyl-1-butanol (MB), and one minor one, ethyl butyrate (EB), varied in their control of the same postharvest fungi and bacteria. Among the three fungi, IBA killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 40, 25, and 45 μL·L –1, respectively. MB killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 75, 100, and 100 μL·L –1, respectively. EB was only able to kill S. sclerotiorum at 100 μL·L –1. Among the three bacteria, IBA killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 5, 12.5, and 12.5 μL·L–1, respectively. MB killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 100, 75, and 100 μL·L–1, respectively. EB did not control growth of the three bacteria. This study demonstrates the need for air circulation in M. albus, MB, and IBA treatments to optimize the efficacy of these potential postharvest agents of disease control.

Free access

Frostgard did not effectively promote the supercooling of flowering `Arking' strawberry (Fragaria ×ananassa Duch.) plants in the presence or absence of ice-nucleation-active bacteria when applied as a spray in laboratory experiments. Frostgard effectively promoted supercooling and reduced the ice propagation rate of aqueous solutions. Detached leaves infiltrated with Frostgard exhibited a negative linear relationship between freezing temperature and Frostgard concentrations from 0% to 20% (by volume). Leaves infiltrated with 20% Frostgard supercooled 1.7C lower than those infiltrated with distilled water. Ice propagation barriers in strawberry plants were observed. Individual leaves froze independently, and a thermal ice propagation barrier sometimes was observed at the crown.

Free access

( Michaud et al., 2002 ). Rhizosphere bacteria can benefit plant development ( Glick, 2004 ; Kokalis-Burelle et al., 2003 ; Lucy et al., 2004 ; Russo, 2006 ; Schulze and Pöschel, 2004 ; Shimshick and Herbert, 1979 ; Zahir et al., 2004 ; Zehnder et al

Free access

Shredded cabbage was packaged in four types of non-perforated and perforated OPP films with initial 10% CO2. In the perforated OPP film with a O2 permeability of 25,000 mL/m2 per day/atm, CO2 remained at about 10%, O2 decreased to 13%, and the shreds showed the best organoleptic quality after 4 days of storage at 10 °C. The bacteria isolated from the shredded cabbage in the perforated MA package were predominantly Gram-negative rod-forms including Enterobacteriaceae and phytopathogenic bacteria, while only lactic acid bacteria (Leuconostoc citreum) was isolated as Gram-positive bacteria. For biological control of the pathogens, two lactic acid bacteria strains (Leuconostoc mesenteroides subsp. mesenteroides and Pediococcus acidilactici) were selected from bacteriocinogenic 6 strains, based on the growth in culture broth under 5% to 20% CO2 atmospheres. Shredded cabbage was inoculated with these two bacteriocin-producing strains, packaged in 10% CO2 perforated MA packaging, and stored at 10 °C. The growth of coliforms and psychotrophic aerobic bacteria was reduced due to antagonistic effect of lactic acid bacteria and the quality of shreds was not affected detrimentally by the strains. These results indicate that the combination of added bacteriocin-producing lactic acid bacteria and 10% CO2 perforated MAP was useful in biopreservation of shredded cabbage.

Free access

Stems of cut rose flowers (Rosa hybrids L., cvs. Sonia, Ilona, Polka, and Frisco) were held in a sodium hypochlorite solution and then placed in distilled water or in a buffer at pH 6.0. After 2 days, many bacteria were found in the basal end of the stems, even when the number of bacteria in the water was below the detection limit. The hydraulic conductance of 5-cm stem segments was reduced whenever the number of bacteria exceeded =106 cfu/g fresh weight. Adding HQC or a buffer at pH 3.0 limited the number of bacteria in stems. Hydraulic conductance of the stems held in these solutions for 2 days was as in stems of freshly harvested flowers. Thus, HQC and low pH prevent vascular blockage by reducing the number of bacteria in the stems. No evidence was found for the hypothesis that HQC and low pH inhibit a stem-induced vascular blockage.

Free access