Y. Henis

A selective medium for improving quantitative isolation ofTrichoderma spp. from soil

ATrichoderma-selective agar medium (TSM) was developed for quantitative isolation ofTrichoderma spp. from soil. Selectivity was obtained by using chloramphenicol as a bacterial inhibitor, and pentachloronitrobenzene, p-dimethylaminobenzenediazo sodium sulfonate and rose-bengal as selective fungal inhibitors. The TSM also contains a low concentration of glucose which still allows relatively rapid growth and sporulation ofTrichoderma, enabling convenient and rapid identification ofTrichoderma colonies. All the 15Trichoderma isolates tested formed colonies and grew well on this medium. Recovery ofTrichoderma from artificially inoculated soils was high and was not affected by soil type or by other microorganisms. A positive correlation was observed betweenTrichoderma added to soil and counts ofTrichoderma colonies on TSM plates. When combined with a soil pellet sampler, the selective medium was also used successfully for recovery of the indigenousTrichoderma population of natural soils.

Microbial degradation of pollutants at high salt concentrations

Though our knowledge on microbial degradation of organic pollutants at high salt concentrations is still limited, the list of toxic compounds shown to be degraded or transformed in media of high salinity is growing. Compounds transformed aerobically include saturated and aromatic hydrocarbons (by certain archaeobacteria), certain aromatic compounds, organophosphorus compounds, and formaldehyde (by halotolerant eubacteria). Anaerobic microbial transformations of toxic compounds occurring at high salt concentrations include reduction of nitroaromatic compounds, and possibly transformation of chlorinated aromatic compounds.

Effects of Lactose, Ethanol and Cycloheximide on the Translocation Pattern of Radioactive Compounds and on Sclerotium Formation in Sclerotium rolfsii

Summary: Protein synthesis and translocation of l-[14C]leucine, d-[14C]glucose and inorganic 32P were enhanced in cultures of Sclerotium rolfsii Sacc. grown on medium supplemented with 0·5% lactose. Ethanol (2%, v/v) inhibited translocation but not protein synthesis. Neither lactose nor ethanol affected the uptake of radioactive substances by the fungal mycelium. Cycloheximide applied to the colony margins prevented sclerotium formation and protein synthesis without inhibiting translocation. It was concluded that translocation and protein synthesis in S. rolfsii are independent processes and are both essential for sclerotium formation.

Biological control of Sclerotium rolfsii and Verticillium dahliae by Talaromyces flavus is mediated by different mechanisms.

ABSTRACT Ten wild-type strains and two benomyl-resistant mutants of Talaromyces flavus were examined for their ability to secrete the cell wall-degrading enzymes chitinase, beta-1,3-glucanase, and cellulase, to parasitize sclerotia of Sclerotium rolfsii, to reduce bean stem rot caused by S. rolfsii, and to secrete antifungal substance(s) active against Verticillium dahliae. The benomyl-resistant mutant Ben(R)TF1-R6 overproduced extracellular enzymes and exhibited enhanced antagonistic activity against S. rolfsii and V. dahliae compared to the wild-type strains and other mu tants. Correlation analyses between the extracellular enzymatic activities of different isolates of T. flavus and their ability to antagonize S. rolfsii indicated that mycoparasitism by T. flavus and biological control of S rolfsii were related to the chitinase activity of T. flavus. On the other hand, production of antifungal compounds and glucose-oxidase activity may play a role in antagonism of V. dahliae by retardation of germination and hyphal growth and melanization of newly formed microsclerotia.

Effect of Azospirillum inoculation on some growth parameters and n-content of wheat, sorghum and panicum

The potential of the nitrogen fixing bacteriumAzospirillum brasilense to enhance development and increase growth of several gramineae was investigated. In both sterilized and non-sterilized systems heading and flowering occurred earlier in the inoculated plants as compared to the noninoculated ones. Total shoot and root weights, total-N content, plant height and leaf length were significantly increased by inoculation.

Movement and retention of Klebsiella aerogenes in soil columns

SummaryThe movement and retention of two strains of Klebsiella aerogenes into saturated soil columns was found to depend on soil type, pH, and bacterial size. The movement of the cells was considered as a specific case of gel permeantion chromatography. The infiltration of the bacterial cells into dry soil columns was affected by soil type, and their upward movement was stopped when the water content of the soil was at or below field capacity level. re]19730907

Microbiological control of plant pathogens

Publisher Summary This chapter discusses a few aspects of microbiological control of plant pathogens, including its occurrence in nature, the most common microbial groups and the mechanisms involved, with emphasis on its practical implications. Microbiological control of plant diseases can be achieved directly, through inoculation, or indirectly, by changing the conditions prevailing in the plants environment, and thus the microbiological equilibrium of its ecosystem, or by a combination of both approaches. The chapter presents a few examples demonstrating the control of plant diseases by inoculation. Microorganisms parasitic to plants constitute a tiny fraction of the microflora and microfauna inhabiting the vicinity and surfaces of plant organs. Disease severity is greatly increased when the pathogen is reintroduced in its pre-sterilized infection site, indicating that the saprophytic microorganisms inhabiting the surfaces of plant organs may serve as a biological buffer zone, preventing the pathogen from infecting its host. Selective pathogen suppression can be achieved by the use of specific chemicals, such as fungicides, which are applied at relatively low dosages. Soil treatment with fumigants, such as chloropicrin, methyl bromide or formalin, results in eradication of both the pathogen and most of the saprophytic microflora.

Yield Increases in Summer Cereal Crops in Israeli Fields Inoculated with Azospirillum

Inoculating Zea mays (three cultivars), Sorghum bicolor, Panicum miliaceum and Setaria italica with nitrogen-fixing bacteria of the genus Azospirillum in Northern Negev and Bet Shean Valley field experiments resulted in significant increases in yield of grain and foliage of commercial value. It was concluded that inoculating summer cereal crops in Israel may save valuable nitrogen fertilizer.

Biological control ofRhizoctonia solani in strawberry fields byTrichoderma harzianum

SummaryTrichoderma harzianum preparations was used in two successive field experiments in commercial strawberry nurseries and fruiting fields. Disease severity ofRhizoctonia solani in daughter plants was reduced by 18–46 % in the treated nursery plots. Infestation of nursery soil with the pathogen, as tested by planting beans in soil samples was reduced by the Trichoderma treatment by up to 92% as compared to the untreated control. A rapid decline of the disease was observed in soil fromT. harzianum treated plots, successively planted with bean seedlings. More isolates ofTrichoderma sp. antagonistic toR. solani, were found in the infested field as compared to the non infested one.Trichoderma harzianum treated plants, transferred to the commercial field gave a 21–37% increase in early yield of strawberries. A combined treatment in the nursery and in the fruiting field resulted in a 20% yield increase as compared to control plots.

Aggregation inAzospirillum brasilense Cd: Conditions and factors involved in cell-to-cell adhesion

Aggregation of the root-inhabiting, asymbiotic N-fixingAzospirillum brasilense Cd (ATCC-29729), was studied. Aggregation occurred towards the end of the exponential phase and during the stationary phase. More aggregates were formed in media supplemented with organic acids than in those containing sugars as a sole carbon source. Maximum growth with no aggregation was obtained in a medium containing both fructose and malate as carbon sources. Aggregation was increased by poly-L-lysine and carbodiimide as well as by increasing the C/N ratio and decreasing combined nitrogen in the growth medium. Aggregates were stable at pH levels of >8 and <6, but dispersed at pH 7.1. Treatment of Azospirillum with NaEDTA resulted in loss of both aggregative capacity and the ability of adsorb to wheat roots without losing cell viability. When extracted bacteria were suspended in their dialysed NaEDTA extract, both their aggregative and adsorptive capacities were restored.The dialysed NaEDTA extract agglutinated bacterial cells and red blood cells, especially of type O. When the extract was run through a sepharose gel, it separated into three main fractions, of which only one showed agglutinating capacity. Gel electrophoresis of this fraction revealed a single band (MW 97,000) which reacted positively to Schiffs reagent and Coomassie brilliant blue R-250, typical to a glycoprotein. Bacterial agglutination by this fraction was strongly inhibited by D-glucose, melibiose and α-metyl glucoside. No evidence as to the involvement of cellulose fibrils in aggregation was found. It is suggested that glycoprotein(s) and glucose residues located on the outer surface of the cells are involved in aggregation of Azospirillum.