SUMMARYActinomycetes isolated from carrot rhizosphere were screened for their in vitro and in viz'o antagonism to Pythium coloratum Vaartaja, a causal agetit of cavity-spot disease of carrots (Daucus carota h.). Forty-five streptomycete and non-strepromycete actinomycete isolates were screened for m ^-j/ro antagonism in a carrot bioassay. Of these, seven which reduced or prevented lesion formatioti were identified using cultural, morphological, physiological, biochemical and cell wall characteristics as Streptomyces janthinus, S. cinerochromogenes, Streptoverticillium netropsis, Actinamadura ruhra, Actinnplanes philippinensis, Micromonospora carbonaceae, and Streptosporangium albidum. All seven isolates tested produced non-volatile atitifungal metabolites, but failed to produce inhibitory volatile compounds. Actinoplanes philippinensis and M. carhonacea grew epiphytically on the hyphae and oospores of P. color afum-The external surface of the oospores of the pathogen was heavily colonized by both hyperparasites, tbeir hyphae were found to coil tightly around the oospore wall, and frequently caused cytoplasmic collapse of oospores. Sporangia of A. philippinensis were often seen to emerge from the colonized hyphae and oospores of P. coloratum. None of the other actinomycete isolates showed hyperparasitism.All seven isolates significantly reduced the incidence of cavity spot in soil artificially infested with the pathogen in the glasshouse. Streptomyces janthinus and Strepto. albidum were the most effective in reducing the disease in inoculated plants. In addition, all the actinomycetes species except Ac. rubra and M. carbonacea, in the presence or absence of the pathogen, significantly (P < 0'05) increased mean fresh root weight compared to the treatment which included P. coloratum only. This study sbows that these actinomycetes have considerable potential for future use as biocontrol agents of cavity spot under natural field conditions. This is the first report of cavity-spot disease of carrots being controlled by microbial antagonists, and is the first report of non-streptomycete actinomycetes to control a Pythium disease.

No abstract

No abstract

No abstract

ABSTRACT:The dielectric and mechanical properties of polystyrene(PS)/acrylonitrile-butadiene rubber (NBR) blends were studied with the aim of improving the insulation properties of NBR. Compatibility investigations, performed with viscosity and dielectric methods and confirmed with the calculated heat of mixing, indicated that such blends were incompatible. To overcome the problem of phase separation between NBR and PS, we chose epoxidized soya bean oil to act as a compatibilizer and added 3% to the blends under investigation. This led to the conclusion that a sample containing 10% PS (either pure or scrap) possessed the most suitable electrical and mechanical properties. For this reason, the sample was chosen for studying the effect of the addition of three types of fillers (quartz, talc, and calcium carbonate) in increasing quantities (up to 80 phr) on the dielectric and mechanical properties. The variation of the dielectric properties with temperature (20 -60°C) was also investigated.

Plectosporium tabacinum root rot disease of white lupine is reported for the ®rst time in Cairo Governorate provinces. Symptoms of the disease appeared on young seedlings as stunting, yellowing and wilting of the foliage. Rotted roots were ®rst became light brown and the lesions progressively extended over the whole root system and became dark brown. Plants died when the whole root system had become infected. For successful biological control of the disease 70 rhizosphere actinomycetes were isolated by the use of normal standard isolation techniques. Three of these isolates were found to be strongly antagonistic against P. tabacinum in vitro. They also signi®cantly reduced the incidence of white lupine root rot disease in soil infested with P. tabacinum in greenhouse trials. The three actinomycete isolates were identi®ed as Streptomyces cyanoviridis, Streptomyces murinus and Streptomyces griseoplanus. ZusammenfassungPlectosporium tabacinum-WurzelfaÈ ule der Weiûlupine (Lupinus termis Forsk.) und deren biologische BekaÈ mpfung durch Streptomyces spp. Es wird zum ersten Mal uÈ ber das Vorkommen der Plectosporium tabacinum-WurzelfaÈ ule der Weiûlupine in den Cairo Governorate-Provinces berichtet. Bei jungen SaÈ mlingen zeigten sich Symptome der Krankheit als ZwergswuÈ chsigkeit, Vergilbungen sowie Blattwelken aus. Die befallenen Wurzeln wurden zuerst hellbraun, die LaÈ sionen breiteten sich progressiv uÈ ber das ganze Wurzelsystem aus und sie wurden dunkel braun. Die P¯anzen starben ab, nachdem das gesamte Wurzelsystem befallen war. Um die Krankheit erfolgreich biologisch zu bekaÈ mpfen, wurden 70 Actinomyceten aus der RhizosphaÈ re mit Hilfe von Standard-Isolationstechniken isoliert. Drei dieser Isolate zeigten eine starke in vitro Hemmung gegenuÈ ber P. tabacinum. In GewaÈ chshausversuchen bewirkten diese StaÈ mme eine signi®-kante Verminderung der WeiûlupinenwurzelfaÈ ule in mit P. tabacinum verseuchten BoÈ den. Diese drei Actinomycet-Isolate wurden als Streptomyces cyanoviridis, S. murinus und S. griseoplanus bestimmt. U. S.

No abstract

No abstract