The effect of epiphytic bacteria population with different ice nucleation activity (INA) on the extent of supercooling of in vitro and leaf tissue disks of greenhouse-grown Capsicum annuum L. plants was determined. Bacterial strains were isolated on PDA and King's B medium from foliar samples of weeds from commercial apple orchards in Cuauhtemoc, Chihuahua, Mexico. Bacteria were screened by colony morphology, fluorescence under UV light, while growin on King's B medium plates and screened for ice-nucleating capability at -5 °C in suspensions of 108 cfu/mL. Ice nucleating (Ice+) and non-ice-nucleating (Ice-) active strains with fluorescent capacity were isolated from symptomless leaf samples. Four bacterial strains were used with different ina as epiphytic population models. Two Pseudomonas syringae strains, Pss29A and PD, from Oregon State Univ., with high Ice+ capability; P. fluorescens A-506, in its Blight Ban™ commercial lyophilized presentation; and UC001, a native fluorescent strain from CIAD-Cuauhtemoc; both Ice-strains. Freezing tests were carried out under controlled conditions. The high Ice+ strains Pss29A and PD increased the temperature of supercooling 2 and 1 °C compared to control samples. The non-inoculated tissue showed damage over 50% at -3 °C and below. Inoculated tissue with Ice+ strains (P. syringae 29A and PD), showed damage superior to 50% at -1 and -2 °C, respectively. Conversely, at none of the temperatures assayed, Ice-strains surpassed 50% damage. These results are of interest for further development of passive strategies towards minimizing damage due to low-temperature exposure of tropical vegetable crops.
Mung bean (Vigna radiata (L.) R. Wilcz.) cuttings are used in rooting bioassays, and nonexperimental variability must be rigorously controlled to obtain meaningful results. This study was conducted to document bacterial disease problems of mung bean and identify the causal organisms. `Berken' seeds were surfaced sterilized and aerated 24 hr before sowing. Nine-day-old seedlings were used in rooting bioassays. Up to 10% of the seedlings and 17% of the cuttings had collapsed stems or wilted leaves. A white and two yellow (Y1 and Y2) bacteria were isolated from diseased cuttings and used in subsequent pathogenicity tests. The Y2 isolate was nonpathogenic. Stems of healthy mung beans inoculated with the white isolate turned brown and collapsed 2 days after inoculation, whereas leaves of plants inoculated with the yellow isolate wilted after 7 days. Standard biochemical and physiological tests revealed that the white isolate was Pseudomonas syringue pv. syringae van Hall and the yellow isolate was Curtobacterium flaccumfaciens subsp. flaccumfaciens (Hedges) Collins and Jones. This research is the first report of a disease in mung bean caused by P.s. pv. syringae. These results demonstrate the need or disease-free seeds being used in bioassays since both pathogens were seed-borne.
Effect of electrolyzed water on total microbial count of several fresh-cut vegetables was evaluated. Electrolyzed water (pH 6.5), containing 20 ppm available chlorine, was produced by electrolysis of salt solution using an electrolyzed neutral water generator, Ameni Clean (Matsushita Seiko Co. Ltd., Osaka, Japan). Fresh-cut vegetables, including carrot slices, chopped bell peppers, trimmed spinach leaves, shredded Japanese radish, and diced potatoes, were treated with electrolyzed water by dipping, rinsing, or bubbling (immersion and flush with air at 25 L/min) for 3 min and then rinsed with running tap water for 1 min. These treatments reduced the total microbial count by about 1 to 2 log units on tissue surface and inside of all vegetables relative to nontreated samples. Since rinsing with tap water also reduced the microbial count by about 1 log unit, the bubbling treatment was the only effective treatment in reducing bacteria on the surface of fresh-cut Japanese radish and potatoes when compared with water-rinsed controls. When samples were not rinsed with tap water after treatment, the microbicidal effect of electrolyzed water was noted on tissue surface of all vegetables even if relative to water-rinsed controls. Electrolyzed water did not affect the tissue pH ranging from 5.7 to 6.1, surface color, and taste of any fresh-cut.
Seeds of `Berken' mung bean [Vigna radiata (L.) R. Wilcz.] were surface-sterilized with NaOCl and then either aerated 24 hours before sowing (routine procedure), planted immediately after the NaOCl treatment, or treated with hot cupric acetate and antibiotics before planting. Nine- or 10-day-old seedlings were used in rooting bioassays. Up to 10% of the seedlings and 17% of the cuttings had collapsed upper stems or wilted leaves. None of the seed treatments completely eliminated the pathogen, but the combination of hot cupric acetate plus antibiotics reduced the quantity of diseased cuttings to 3.3%. A white and two yellow-pigmented (Y1 and Y2) bacteria were isolated from diseased cuttings and used in subsequent pathogenicity tests. The Y2 strain was nonpathogenic. Stems of plants inoculated with the white strain turned brown and collapsed 2 days after inoculation, whereas leaves of plants inoculated with the Y1 strain wilted after 7 days. Electron microscopy, fatty acid analysis, and standard biochemical and physiological tests were used to identify the white strain as Pseudomonas syringae pv. syringae van Hall and the Y1 strain as Curtobacterium flaccumfaciens ssp. flaccumfaciens (Hedges) Collins and Jones. These results emphasize that seeds of mung bean should be checked for seedborne pathogens to avoid experimental artifacts.
Mineralization of N from nonviable cells of Brevibacterium lactofermentum (Okumura et al.) mixed into soilless substrate in elution columns occurred largely during the first 5 weeks with a peak between 2 and 3 weeks. Over a 12-week period, 73% of the total N was recovered in the eluent. To prolong the period of N release to meet the requirements of a slow-release fertilizer, the bacterium was bonded to kraft lignin, a polyphenolic substance highly resistant to degradation. To retard mineralization further, the bacterium-lignin mixture was reacted with formaldehyde to form amino cross-links within and between protein chains. Bonding to lignin was undesirable because N release occurred during the same period as from the bacteria unbound to lignin and the total amount of N recovered was reduced to only 42%. Cross-linking with formaldehyde was less desirable since N was released mainly during the first 4 weeks with a peak during the first elution (0 time) and the total amount of N released was even lower than for the bacterium-lignin mixture. Additions of urea to the latter reaction did not satisfactorily improve subsequent N mineralization. In a second set of treatments lignin was withheld and the bacterium was reacted with weights of formaldehyde (a.i.) equivalent to 0.1%, 0.5%, 1.0%, 5.0%, and 10.0% of the dry weight of bacterium. Formaldehyde quantities ≤1.0% either had no effect or lowered the mineralization of N without altering time of release. Five percent and 10% formaldehyde successfully reduced release of N during the first 4 weeks and increased it thereafter. The best rate was 5%. In this treatment N was released from week 2 through the end of the test (12 weeks). Peak release occurred at 6 weeks. This resulting N source, while not a stand alone product, does have a slow-release property that could lend itself to use in combination with other slow-release N sources.
Stock plants of `Shepody' and `Yukon Gold' potato (Solarium tuberosum L.) were grown in a greenhouse and irrigated with city water. Contamination rate of stem explant tissue cultures excised from these stock plants was 50% to 100%. A comparison of the microorganisms isolated from the contaminated cultures and from 0.22-μm filter disks through which 20 liters of city water had passed revealed the presence of similar bacterial floras. Five genera of bacteria (Listerium spp., Corynebacterium spp., Enterobacter spp., Pasteurella spp., and Actinobacillus spp.) were isolated from contaminated cultures and cultured filter disks. Watering greenhouse-grown stock plants with filtered city water decreased contamination of stem explant cultures 30% to 50%. Installing an ultraviolet light water-sterilizing unit at the greenhouse inlet point effectively reduced contamination.
The rhizospheres of creeping bentgrass (Agrostis palustris Huds.) and hybrid bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy) putting greens were sampled quarterly for 4 years. Six bacterial groups, including total aerobic bacteria, fluorescent pseudomonads, actinomycetes, Gram-negative bacteria, Gram-positive bacteria, and heat-tolerant bacteria, were enumerated. The putting greens were located in four geographic locations (bentgrass in Alabama and North Carolina; bermudagrass in Florida and South Carolina) and were maintained according to local maintenance practices. Significant effects were observed for sampling date, turfgrass species and location, with most variation due to either turfgrass species or location. Bentgrass roots had significantly greater numbers of fluorescent pseudomonads than bermudagrass roots, while bermudagrass roots had significantly greater numbers of Gram-positive bacteria, actinomycetes and heat-tolerant bacteria. The North Carolina or South Carolina locations always had the greatest number of bacteria in each bacterial group. For most sampling dates in all four locations and both turfgrass species, there was a minimum, per gram dry root, of 107 CFUs enumerated on the total aerobic bacterial medium and a minimum of 105 CFUs enumerated on the actinomycete bacterial medium. Thus, it appears that in the southeastern U.S. there are large numbers of culturable bacteria in putting green rhizospheres that are relatively stable over time and geographic location.
Ten bacteria were isolated from the in vitro shoot cultures of different tansy (Tanacetum vulgare) genotypes. All isolates were Gram-negative. Five isolates belonged to Enterobacteriaceae, three isolates were strains of fluorescent Pseudomonas, and two isolates were strains of other aerobic bacteria. The combined treatment with gentamicin (50 mg·L–1) and rifampicin (25 mg·L–1) prevented the growth of all bacteria, whereas none of the antibiotics (ampicillin, cefotaxime, rifampicin, gentamicin, or streptomycin) controlled all bacteria when used alone. The antibiotics ranged based on their increasing adverse effects on shoot cultures as follows: rifampicin, cefotaxime, and gentamicin. Increased antibiotic concentration reduced the initiation and growth rates of shoots, roots and calli with some exceptions. Low concentrations of gentamicin and cefotaxime both increased the growth rate and shoot number per plant. Rifampicin stimulated the root growth of some of the biotypes tested. The growth rate of calli increased significantly in the presence of both gentamicin (25 mg·L–1) and rifampicin (25 mg·L–1) in the growth media, whereas the use of either antibiotic alone reduced the calli growth relative to the control. Viability of tansy protoplasts was enhanced by rifampicin and to a lesser extend by gentamicin and cefotaxime. The growth of bacteria isolated from tansy tissue culture can be prevented with a combined gentamicin and rifampicin treatment. The growth rate of plants decreased slightly when grown in the media supplemented with the same antibiotic combination. However, the growth retardation was not permanent, and the plants recovered and grew vigorously when transferred to antibiotic free medium.
Abstract
Rooted twig cuttings of ‘Jefferson’ peach [Prunus persica (L.) Batsch] infected or noninfected with phony peach disease were divided into nonphony, medium phony, and severe phony based on symptoms and on Fastidious, gram-negative, xylemlimited bacteria (PPXLB) counts. During the dormant season, the rooted plants were subjected to cold treatments of -11.7°, -14.4°, -17.9°, -20.0°, and -21.6°C in cold chambers. Plants with higher PPXLB counts exhibited more cold injury than plants with lower counts.
Abstract
‘Healani’, ‘Homestead-24’, ‘Walter’, and ‘Flora-Dade’ tomatoes (Lycopersicon esculentum Mill.) were grown with 0, 93, 186, 372, or 744 kg K/ha during spring and fall to determine the influence of K rate, cultivar, and season on the separate fruit disorders of graywall (GW) and blotchy ripening (BR). Susceptibility to GW was determined by inoculating a GW-inducing type of bacteria, Erwinia herbicola (Dye), into the outer pericarp of immature green fruit. All 4 cultivars developed more GW without added K than with it during the spring season. In both field and greenhouse conditions, ‘Flora-Dade’ and ‘Homestead-24’ were more resistant to GW than ‘Healani’ and ‘Walter’. Natural GW, contrasted to bacterially induced GW, occurred in ‘Healani’ and ‘Homestead-24’ fruit grown with low K concentrations in a sand culture experiment. Both cultivars were free of natural GW with the high-K treatment. ‘Flora-Dade’ was resistant to natural GW under all K treatments. Fruit from all cultivars had significantly less BR with K fertilization in both seasons. External blotchy ripening (EBR) and internal blotchy ripening (IBR) were more severe in the spring than in the fall. ‘Healani’ showed resistance to yellow shoulder, the primary EBR symptom, which was severe during the spring in all other culti vars. ‘Healani’ was generally the most BR-resistant cultivar and ‘Flora-Dade’ the most BR-susceptible. Pericarp K concentration increased with K rate in all cultivars during both seasons, but differences in susceptibility to BR between cultivars were not associated with differences in pericarp K, Ca, Mg, or P content.