Evaporative cooling pad attenuates osmotic stress in closed-loop irrigated greenhouse roses

Ecological and economic considerations motivate the use of closed-loop irrigation to grow greenhouse crops on artificial substrates, submitting plants to increased osmotic stress due to heightened solute concentration of the irrigation solution. High solute concentration of re-circulated irrigation water, measured as electrical conductivity (EC), lowered the transpiration rate of flowering rose stems measured by the heat pulse method. The operation of an evaporative cooling pad decreased the transpiration rate by diminishing the water vapor deficit of the air in the greenhouse and slowed the rate of solute accumulation. Weaker evaporative demand also attenuated salinity induced decrease of transpiration rate. Leaf water potential and stomatal conductance corroborated that the wet-pad and fan alleviated osmotic stress caused by high concentration of the re-circulated irrigation solution.     

Short-lived protection of pea plants against Mycosphaerella pinodes by prior inoculation with Pseudomonas phaseolicola

Pea plants,Pisum sativum cv. Eminent, were inoculated by spraying with a suspension (10⁸ cells/ml) ofPseudomonas phaseolicola, a bacterium not pathogenic to pea. At intervals of 0,2,4,6, or 8 days the same plants were challenged with a conidial suspension (10⁶ conidia/ml) of the peapathogenic fungusMycosphaerella pinodes. Periodically, leaf samples were examined for development of symptoms and phytoalexin content.Up to 6 days after inoculation with the non-pathogenic bacterium the plants were protected against the pathogenic fungus. Pisatin, however, seemed not to be responsible for the observed protection.Samenvatting Erwteplanten, cv. Eminent, werden bespoten met een suspensie (10⁸ bacteriën/ml) vanPseudomonas phaseolicola, een bacterie die niet pathogeen is voor erwt. Na 0,2,4,6, of 8 dagen werden dezelfde planten opnieuw geïnoculeerd, nu echter met een conidiënsuspensie (10⁶ conidiën/ml) van de voor erwt pathogene schimmelMycosphaerella pinodes. Periodiek werden bladmonsters beoordeeld naar ontwikkeling van symptomen en aanwezigheid van fytoalexinen.Tot 6 dagen na de inoculatie met de niet-pathogene bacterie bleken de planten—in afnemende mate — beschermd tegen aantasting door de pathogene schimmel. Aangezien er geen positieve correlatie bleek te bestaan tussen de pisatineconcentratie en de mate van bescherming, leek pisatine voor deze bescherming niet verantwoordelijk.     

Multiple Resistance in the Larger House Fly Musca domestica in Germany

Populations of the housefly Musca domestica isolated from farms in different German districts with strong resistance problems were compared to laboratory strains with varying resistance spectra. Resistance against pyrethroids, organophosphates and carbamates was tested using impregnated filter papers, and by topical application using a susceptible housefly strain (origin WHO) for comparison. The multi-resistant fly strains tested had a strong resistance against these insecticide groups, ranging from 37- to >10000-fold for organophosphates and 150- to >6600-fold for pyrethroids. The constituent enantiomer pairs of the α-cyano-pyrethroid cyfluthrin were tested, as was beta-cyfluthrin. With respect to multi-resistant fly strains, the isomers II and IV had the best activity, with LD₅₀ values of 0·012 and 0·014 μg per fly, respectively. In addition, different groups of insect growth regulators (juvenile hormone analogues, chitin synthesis inhibitors and one triazine derivative) were tested in a special larvicidal test. The chitin synthesis inhibitors were quite effective against multi-resistant M. domestica strains except for one strain with strong resistance against chitin synthesis inhibitors, developed after extensive treatments with benzoylphenylureas for several years. The fly strains tested were not resistant against cyromazine. Additionally, the insecticides were combined with the synergists piperonyl butoxide, tributylphosphorotrithioate (DEF) and Cibacron blue and tested against the fly strain with the strongest resistance spectrum (‘Grimm’) in comparison to the susceptible strain (‘WHO-N’). Piperonyl butoxide had the greatest effect on the efficacy of cyfluthrin followed by Cibacron blue and DEF. In a parallel investigation with susceptible and resistant house fly strains, different enzyme activities related with resistance mechanisms were tested, e.g. glutathione S-transferase (3·5-fold) and mixed-function oxidase (2·3-fold). Implications of these results for management of insecticide resistance in M. domestica are discussed.     

Uptake,distribution and metabolic fate of 3H-triforine in plants .I. Short-term experiments

Most of the label, present in the roots of bean, tomato and barley seedlings after short-term root-treatment with ³H-triforine, appeared only weakly adsorbed on to the root tissue and was desorbed after transplanting in fungicide-free soil. Label taken up accumulated almost exclusively in the leaves present at the time of treatment; all leaves expanding after termination of the treatment remained virtually devoid of radioactivity. In “adult” plants label was usually present in a concentration gradient from roots to youngest leaves; in tomato plants, however, distribution of label was rather irregular. Time-course studies with bean and barley plants revealed that the aerial parts were gradually supplied with label, from old to youngest leaves, the maximum relative accumulation of radioactivity slowly moving acropetally. Under the experimental conditions chosen, triforine was converted nearly quantitatively to one metabolite, which almost certainly is different from any known non-enzymic breakdown product of the fungicide.     

Diastereomer-selective resistance in Cladosporium cucumerinum to triazole-type fungicides

Diastereomers of triazole-type fungicides behaved differently with respect to their fungitoxicity towards wild-type strains of Cladosporium cucumerinum and strains resistant to ergosterol biosynthesis inhibitors. With increasing resistance to the fungicide ‘as a whole’, the difference in resistance to the two diastereomers of triadimenol became progressively smaller, whereas for the other triazole derivatives, this difference became progressively larger. The possible consequences of such phenomena for the practical use of diastereomeric fungicides are discussed.     

The use of attenuated isolates of <Emphasis Type="Italic">Pepino mosaic virus</Emphasis> for cross-protection

Pepino mosaic virus (PepMV) has recently emerged as a highly infectious viral pathogen in tomato crops. Greenhouse trials were conducted under conditions similar to commercial tomato production. These trials examined whether tomato plants can be protected against PepMV by a preceding infection with an attenuated isolate of this virus. Two potential attenuated isolates that displayed mild leaf symptoms were selected from field isolates. Two PepMV isolates that displayed severe leaf symptoms were also selected from field isolates to challenge the attenuated isolates. The isolates with aggressive symptoms were found to reduce bulk yields by 8 and 24% in single infections, respectively. Yield losses were reduced to a 0–3% loss in plants that were treated with either one of the attenuated isolates, while no effects were observed on the quality of the fruits. After the challenge infection, virus accumulation levels and symptom severity of the isolates with aggressive symptoms were also reduced by cross-protection. Infection with the attenuated isolates alone did neither affect bulk yield, nor quality of the harvested tomato fruits.