Rahnella spp. are commonly isolated from onion (Allium cepa) bulbs and are weakly pathogenic.

AIMS: Bacterial decays of onion bulbs have serious economic consequences for growers, but the aetiologies of these diseases are often unclear. We aimed to determine the role of Rahnella, which we commonly isolated from bulbs in the United States and Norway, in onion disease. METHODS AND RESULTS: Isolated bacteria were identified by sequencing of housekeeping genes and/or fatty acid methyl ester analysis. A subset of Rahnella spp. strains was also assessed by multilocus sequence analysis (MLSA); most onion strains belonged to two clades that appear closely related to R. aquatilis. All tested strains from both countries caused mild symptoms in onion bulbs but not leaves. Polymerase chain reaction primers were designed and tested against strains from known species of Rahnella. Amplicons were produced from strains of R. aquatilis, R. victoriana, R. variigena, R. inusitata and R. bruchi, and from one of the two strains of R. woolbedingensis. CONCLUSIONS: Based on binational testing, strains of Rahnella are commonly associated with onions, and they are capable of causing mild symptoms in bulbs. SIGNIFICANCE AND IMPACT OF THE STUDY: While Rahnella strains are commonly found within field-grown onions and they are able to cause mild symptoms, the economic impact of Rahnella-associated symptoms remains unclear.

Evaluation of Six Models to Estimate Ascospore Maturation in Venturia pyrina.

Estimates of ascospore maturity generated by models developed for Venturia pyrina in Victoria, Australia (NV and SV), Oregon, United States (OR), and Italy (IT) or for V. inaequalis in New Hampshire, United States (NH-1) or modified in Norway (NH-2) were compared with observed field ascospore release of V. pyrina from 21 site-year combinations. The models were also compared with ascospore release data from laboratory assays. In the laboratory assays, the forecasts of the NH-1 and NH-2 models provided the best fit to observed spore release. Under field conditions, the lag phases and slope coefficients of all models differed from those of observed release of ascospores. Identifying the precise time of bud break of pear to initiate degree-day accumulation was problematic at both Australian sites. This resulted in a higher deviance between bud break and first released ascospore compared with the sites in Norway and Belgium. Linear regressions of observed release against forecasted maturity generated similarly high concordance correlation coefficients. However, where differences were noted, they most often favored models that included adjustment for dry periods. The NH-2, IT, and NV models using pooled data also provided the most accurate estimates of 95% ascospore depletion, a key event in many disease management programs.

Activation of muscarinic receptors elicits inotropic responses in ventricular muscle from rats with heart failure through myosin light chain phosphorylation.

BACKGROUND AND PURPOSE: Muscarinic stimulation increases myofilament Ca(2+) sensitivity with no apparent inotropic response in normal rat myocardium. Increased myofilament Ca(2+) sensitivity is a molecular mechanism promoting increased contractility in failing cardiac tissue. Thus, muscarinic receptor activation could elicit inotropic responses in ventricular myocardium from rats with heart failure, through increasing phosphorylation of myosin light chain (MLC). EXPERIMENTAL APPROACH: Contractile force was measured in left ventricular papillary muscles from male Wistar rats, 6 weeks after left coronary artery ligation or sham surgery. Muscles were also frozen, and MLC-2 phosphorylation level was quantified. KEY RESULTS: Carbachol (10 micromol.L(-1)) evoked a positive inotropic response only in muscles from rats with heart failure approximating 36% of that elicited by 1 micromol.L(-1) isoproterenol (20 +/- 1.5% and 56 +/- 6.1% above basal respectively). Carbachol-evoked inotropic responses did not correlate with infarction size but did correlate with increased left ventricular end diastolic pressure, heart weight/body weight ratio and lung weight, primary indicators of the severity of heart failure. Only muscarinic receptor antagonists selective for M(2) receptors antagonized carbachol-mediated inotropic effects with the expected potency. Carbachol-evoked inotropic responses and increase in phosphorylated MLC-2 were attenuated by MLC kinase (ML-9) and Rho-kinase inhibition (Y-27632), and inotropic responses were abolished by Pertussis toxin pretreatment. CONCLUSION AND IMPLICATIONS: In failing ventricular muscle, muscarinic receptor activation, most likely via M(2) receptors, provides inotropic support by increasing MLC phosphorylation and consequently, myofilament Ca(2+) sensitivity. Enhancement of myofilament Ca(2+) sensitivity, representing a less energy-demanding mechanism of inotropic support may be particularly advantageous in failing hearts.

Induced Resistance as a Possible Means to Control Diseases of Strawberry Caused by Phytophthora spp.

Two putative elicitors of disease resistance (acibenzolar-S-methyl and chitosan) were tested for their effect on crown rot (Phytophthora cactorum) in strawberry. The effect of both compounds was enhanced when the time between treatment and inoculation was prolonged from 2 to 20 days. There were no significant differences between treatments when the concentration of acibenzolar-S-methyl was increased from 10 to 1,000 µg a.i./plant. The lowest tested concentrations of chitosan (10 and 50 µg a.i./plant) resulted in a lower disease score compared with the highest concentrations (250 or 1,000 µg a.i./plant). There were no differences in disease score between treatment with fosetyl-Al, acibenzolar-S-methyl, or chitosan when applied 5 or 15 days before inoculation. The effect of acibenzolar-S-methyl and chitosan also was tested against P. fragariae var. fragariae in alpine strawberry (Fragaria vesca var. alpina cv. Alexandria). Chitosan had no effect, whereas fosetyl-Al and all treatments with acibenzolar-S-methyl (50 or 250 µg a.i./plant; 5, 10, 20, or 40 days before inoculation) reduced the severity of the disease. There were no significant differences between acibenzolar-S-methyl and fosetyl-Al when applied at the same time. Acibenzolar-S-methyl and chitosan at concentrations of 0.5, 5, 50, and 500 µg a.i. ml-1 in V8 juice agar were tested for possible effects on P. cactorum and P. fragariae var. fragariae in vitro. Only chitosan at concentrations of 50 and 500 µg a.i. ml-1 had a growth-retarding effect on P. cactorum. Both acibenzolar-S-methyl and chitosan at a concentration of 500 µg a.i. ml-1 reduced the growth rate of P. fragariae var. fragariae.