Preventive Fungicidal Control of Cytospora leucostoma in Peach Orchards in Colorado.

In western Colorado, Cytospora leucostoma is ubiquitous in peach orchards and has developed into a major limiting factor of peach production. The pathogen is unable to invade healthy intact phloem tissue of the tree, but instead, it requires a wound as a mode of entry. Bark injuries caused by cold and pruning in commercial orchard systems provide infection courts that, in suitable environment conditions, can lead to many successful fungal infections. Preventive fungicide control is an integral component of management in tree fruit production. Eighteen fungicides were tested at selected label dose rates for C. leucostoma control. All treatments were initially tested in vitro in fungicide-amended media dishes. Successful treatments were then tested under controlled conditions on detached peach branch segments. Effective fungicides identified in the laboratory assays (thiophanate-methyl, captan, lime sulfur, and copper hydroxide) were further tested as spray applications in the field and as wound sealant applications in combination with latex paint and kaolin clay. Of the treatments evaluated, thiophanate-methyl, captan, 50% latex paint, thiophanate-methyl amended in 50% latex paint, captan amended in 50% latex paint, and lime sulfur were most effective in reducing C. leucostoma necrotic area. Copper hydroxide was ineffective in all field trials and in some instances, yielded larger necrotic areas than the nontreated positive control shoots.

New Outbreaks of Bacterial Wilt of Dry Bean in Nebraska Observed from Field Infections.

Bacterial wilt caused by Curtobacterium flaccumfaciens pv. flaccumfaciens was one of the more problematic diseases of dry bean (Phaseolus vulgaris L.) throughout the irrigated High Plains (Colorado, Nebraska, and Wyoming) in the 1960s and early 1970s, but has not been observed since that time. However, in August of 2003, plants exhibiting wilting and irregular, interveinal necrotic foliar lesions surrounded by a bright yellow border were found in three dry bean fields (market class Great Northern) in Scotts Bluff County, Nebraska. During 2004, plants exhibiting identical symptoms were additionally found occurring in more than 40 dry bean fields in western Nebraska. Affected fields were planted with dry bean from multiple market classes and seed sources, including yellow bean, Great Northern bean, and pinto bean, and incidence varied from trace levels to 80 to 90%. Isolations were made from leaf and stem tissues and seeds collected after harvest from infected plants, and all yielded slow-growing, creamy yellow or orange, fluidal colonies on nutrient broth-yeast extract medium. The bacterium was identified as C. flaccumfaciens pv. flaccumfaciens based on cell morphology (coryneformshaped motile rods), positive Gram stain and KOH reactions, fatty acid profiles, and BIOLOG (Hayward, CA) identifications. Great Northern (cv. Orion) plants were inoculated by bacterial suspensions (5 × 107 CFU/ml) injected into leaf axils adjacent to the first fully expanded trifoliolate and were incubated in the greenhouse under ambient conditions fluctuating between 24 and 35°C. Wilting symptoms developed 7 days after inoculation with foliar necrosis and yellowing symptoms appearing after 24 days. Identical bacterial colonies were reisolated from inoculated tissues, completing Koch's postulates. Although recent reports of wilt have been made in North Dakota (2) and western Canada (1) in 1995 and 2002, respectively, they were based only on the presence of discolored seeds observed in dockage from processing plants after harvest. To our knowledge, this report represents the first widespread observations of bacterial wilt from field infections in Nebraska in more than 30 years. References: (1) J. R. Venette et al. Plant Dis. 79:966, 1995. (2) T. F. Hsieh et al. Plant Dis: 86:1275, 2002.

Sexual Stage Development of Uromyces appendiculatus and Its Potential Use for Disease Resistance Screening of Phaseolus vulgaris.

In June 1989, pycnia and aecia of the bean rust pathogen were observed in eastern Colorado on volunteer plants of pinto bean cvs. UI 114 and UI 126 that grew from seed that remained in the field after harvest the previous season. Harvested aeciospores were viable and produced typical reddish-brown uredinia on unifoliolate leaves of UI 114 seedlings in the greenhouse. Evidence of bean rust overwintering has been confirmed in 10 years from 1989 to 2002 in eastern Colorado and the surrounding region. Overwintering conditions were reproduced at Fort Collins, CO in fall 1992 and spring 1993. Debris treatments had significantly higher disease incidence on stems, total number of lesions on stems, disease incidence on leaves, and total number of lesions on leaves of plants of pinto cvs. UI 114 and Olathe than plants without debris. Bean leaves of both cultivars had significantly higher disease incidence than stems. There also was an increased incidence of aecial infection for UI 114 seedlings that germinated through leaf debris with rust compared with stem debris under greenhouse conditions with abundant moisture. Bean leaf debris smaller than 0.36 mm in diameter resulted in significantly more aecial lesions on UI 114 than larger leaf debris and stem debris. Additional greenhouse experiments demonstrated that diverse collections of naturally occurring, overwintered, rust-infested bean debris from eastern Colorado produced different levels of pycnial and aecial infection on pinto cvs. UI 114, Olathe, and Chase. Chase, currently resistant to the uredinial stage of the prevalent bean rust races in Colorado and surrounding states, had a low incidence of aecial lesions on seedling stems when exposed to pycnial and aecial stages in the greenhouse. These observations indicate that selection of bean rust resistance genes should rely on multiple sources of resistant germ plasm to counter the potential increase in new races that could derive from sexual recombination in bean-production regions.

Effect of chronic intermittent administration of inhaled tobramycin on respiratory microbial flora in patients with cystic fibrosis.

Pseudomonas aeruginosa endobronchial infection causes significant morbidity and mortality among cystic fibrosis patients. Microbiology results from two multicenter, double-blind, placebo-controlled trials of inhaled tobramycin in cystic fibrosis were monitored for longitudinal changes in sputum microbial flora, antibiotic susceptibility, and selection of P. aeruginosa isolates with decreased tobramycin susceptibility. Clinical response was examined to determine whether current susceptibility standards are applicable to aerosolized administration. Treatment with inhaled tobramycin did not increase isolation of Burkholderia cepacia, Stenotrophomonas maltophilia, or Alcaligenes xylosoxidans; however, isolation of Candida albicans and Aspergillus species did increase. Although P. aeruginosa tobramycin susceptibility decreased in the tobramycin group compared with that in the placebo group, there was no evidence of selection for the most resistant isolates to become most prevalent. The definition of resistance for parenteral administration does not apply to inhaled tobramycin: too few patients had P. aeruginosa with a tobramycin MIC >/=16 microgram/mL to define a new break point on the basis of clinical response.

Intermittent administration of inhaled tobramycin in patients with cystic fibrosis. Cystic Fibrosis Inhaled Tobramycin Study Group.

BACKGROUND AND METHODS: We conducted two multicenter, double-blind, placebo-controlled trials of intermittent administration of inhaled tobramycin in patients with cystic fibrosis and Pseudomonas aeruginosa infection. A total of 520 patients (mean age, 21 years) were randomly assigned to receive either 300 mg of inhaled tobramycin or placebo twice daily for four weeks, followed by four weeks with no study drug. Patients received treatment or placebo in three on-off cycles for a total of 24 weeks. The end points included pulmonary function, the density of P. aeruginosa in sputum, and hospitalization. RESULTS: The patients treated with inhaled tobramycin had an average increase in forced expiratory volume in one second (FEV1) of 10 percent at week 20 as compared with week 0, whereas the patients receiving placebo had a 2 percent decline in FEV1 (P<0.001). In the tobramycin group, the density of P. aeruginosa decreased by an average of 0.8 log10 colony-forming units (CFU) per gram of expectorated sputum from week 0 to week 20, as compared with an increase of 0.3 log10 CFU per gram in the placebo group (P<0.001). The patients in the tobramycin group were 26 percent (95 percent confidence interval, 2 to 43 percent) less likely to be hospitalized than those in the placebo group. Inhaled tobramycin was not associated with detectable ototoxic or nephrotoxic effects or with accumulation of the drug in serum. The proportion of patients with P. aeruginosa isolates for which the minimal inhibitory concentration of tobramycin was 8 microg per milliliter or higher increased from 25 percent at week 0 to 32 percent at week 24 in the tobramycin group, as compared with a decrease from 20 percent at week 0 to 17 percent at week 24 in the placebo group. CONCLUSIONS: In a 24-week study of patients with cystic fibrosis, intermittent administration of inhaled tobramycin was well tolerated and improved pulmonary function, decreased the density of P. aeruginosa in sputum, and decreased the risk of hospitalization.

Dependence of discharge rate on sound pressure level in cochlear nerve fibers of the alligator lizard: implications for cochlear mechanisms.

1. Rate-level functions for individual cochlear nerve fibers of the alligator lizard, Gerrhonotus multicarinatus, were generated by measuring a fiber's driven discharge rate (the difference between the average discharge rates in the presence and absence of a tone burst) as a function of sound pressure level. 2. When plotted in double logarithmic coordinates, the rate-level function approaches a straight line at low sound pressure levels and saturates at high levels. Thus the rate-level function is a saturating power function of sound pressure. We developed an algorithm to estimate the exponent of the straight-line portion of the function. When tested on simulated data with known parameters, the algorithm provided unbiased estimates of the exponent. 3. Nerve fibers innervating two distinct regions of the alligator lizard's auditory organ, the free-standing region and the tectorial region, have differing rate-level functions. 4. The mean exponent estimate of the rate-level functions of fibers innervating the free-standing region is approximately 2 at all frequencies. For stimulus frequencies at the characteristic frequency (CF), the mean value was 2.1 +/- 0.10 (SE, n = 131). For stimulus frequencies above and below CF, the mean exponent estimates were 2.1 +/- 0.13 (n = 49) and 2.1 +/- 0.11 (n = 34), respectively. A value of 2 is expected for a broad class of nonlinear systems. 5. The mean exponent estimates of the rate-level functions of fibers innervating the tectorial region were 3.0 +/- 0.30 (n = 32) for stimulus frequencies at CF, 2.5 +/- 0.33 (n = 3) for stimulus frequencies below CF, and 1.0 +/- 0.21 (n = 16) for stimulus frequencies above CF. Both the deviation from square-law behavior at CF and the frequency dependence of the exponent imply that nonlinear processing in the tectorial region differs intrinsically from that in the free-standing region. 6. For free-standing fibers, the saturation rate of the rate-level function (the maximum driven rate) is independent of stimulus frequency. This suggests that, in the free-standing region, 1) the alternating (AC) component of the receptor potential makes no significant contribution to the average rate of discharge and 2) neural saturation results from a process that occurs after the narrow-band frequency-selective process(es). 7. In tectorial fibers, the saturation rate is a bandpass function of sound frequency, with a broad peak between 150 and 300 Hz. This function appears to be common to all tectorial fibers.(ABSTRACT TRUNCATED AT 400 WORDS)