Non-chemical approach to soilborne pest management – organic amendments

Chemical soil disinfestation often leads to the eradication of most microbial residents. This creates a microbial vacuum, which often leads to a rebounding of pathogens. This in turn may cause even more damage than those originally targeted for control. Soils, especially those with low microbial populations are more vulnerable to pathogen reinvasion following fumigation. A non-chemical approach to improve the control of soilborne pests involves combining organic amendments with soil solarization. Heating soils, that have been covered with plastic film and amended with suitable organic materials, actuates a chain reaction of chemical and microbial degradation, which leads to the generation of toxic compounds in vapor and liquid phases in the soil. The generation of toxic compounds increases with temperature. These compounds accumulate under the plastic mulch, and enhance toxicity against soil flora and fauna, especially soilborne plant pathogens. The plastic mulch traps the volatile compounds and creates an atmosphere in the soil that enhances degradation of the organic matter. The toxicity of the generated volatile compounds is expected to be higher at the high soil temperature prevailing during solarization. At the end of the process, the soil contains less pathogens, and different microflora, which may suppress reestablishment of pathogens in the soil. The effect of solarizing organically amended soil as a control method was validated under commercial field conditions. A long-term effect of the combined treatments was also evident.     

Phytopathology in Israel: nine decades of research

Four major and formative events have shaped the profession of plant pathology in Israel: (i) The establishment, in 1921, of the first Department of Plant Pathology, at the Agricultural Experiment Station. (ii) The establishment, in 1942, of the Faculty of Agriculture, at The Hebrew University of Jerusalem. (iii) The first congress of plant pathology in Israel in 1967, followed by 29 more meetings in the coming 42 years. (iv) The foundation of the Israeli Phytopathological Society in 1970. The various studies carried out during these nine decades have covered all major developments and issues in plant pathology.     

Weakening and Delayed Mortality of Fusarium oxysporum by Heat Treatment: Flow Cytometry and Growth Studies

ABSTRACT Survival of Fusarium oxysporum f. sp. niveum following heat treatments was studied using flow cytometric, physiological, and microscopic assays. We exposed germinating conidia to sublethal temperatures from 36 to 42 degrees C for 60 min, followed by rhodamine 123 staining and flow cytometry, and found increasing levels of fluorescence that reflect a change in mitochondrial membrane potential, indicating a weakening induced by stress. Viability of conidia or germinating conidia of the fungus exposed to heat decreased with increasing temperature, as assessed by fluorescent staining. However, viability was higher than that assessed with the 5-day-long plate count method and was further reduced 13 and 24 h after treatment, suggesting delayed mortality of the heat-treated germinating conidia. Delayed mortality was substantiated by observing these conidia with light and fluorescent scanning electron microscopy and by subculturing single germinating conidia that had been previously heated. Programmed cell death was not observed in heat-treated conidia or germinating conidia of F. oxysporum based on the detection of plasma membrane phosphatidylserine translocation, cell-cycle measurements, detection of DNA fragmentation, or microscopic observation of apoptotic bodies. We hypothesize that propagules, which survived the heating and apparently are alive, may undergo further irreversible detrimental processes, eventually leading to their death by yet unidentified mechanisms. These findings suggest that pathogen propagules also might be affected under lower temperatures, possibly facilitating pathogen control by heating.