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Extensive studies showed that no disease was caused when seeds of different forage grasses were inoculated with Xanthomonas campestris pv. graminis. The disease could easily be induced by infecting the plants in the root system, leaves or flower. The inoculation site in the leaf proved to be of vital importance for the development of the disease. Wilting symptoms were quickly induced when the pathogen was inoculated near the leaf base. Plants in root-contact with diseased plants showed disease symptoms. It is not known whether these symptoms were caused by the bacteria or by toxins released by nearby diseased plants. Cross inoculation trials on different grass varieties revealed that different pathovars exist in the group of xanthomonads, pathogenic to forage grasses. Some have a broad host range whereas others are more limited to a single plant genus. Field trials suggest that in Belgian climatic conditions, the losses caused by bacterial wilt are rather limited. [ABSTRACT FROM AUTHOR]

Anker's medium with glucose and Thornton's medium were most suitable for growing Enterobacter aerogenes and Bacillus subtilis respectively, antagonists of P. cactorum, the causal agent of apple crown rot. Calcium nitrate was the best source of nitrogen for growing cultures of E. aerogenes and B. subtilis. E. aerogenes produced the maximum amount of antifungal substance at 200 and 400 mg/1 of nitrogen in the medium. Phosphate supplied either in the potassium or calcium form did not change the growth of either antagonist. An addition of 200 mg/1 of N and 400 mg/1 of P significantly enhanced the production of antifungal substance by E. aerogenes on Anker's medium with glucose. Thornton's medium supplemented with 200 mg/1 of N and 100 mg/1 of P produced the maximum amount of antifungal substance from B. subtilis. Generally, soil extracts without enrichment did not support the growth of either antagonist; E. aerogenes required at least 400 mg/1 of both N and P while B. subtilis required 200 mg/1 of N and 800 mg/1 of P for the maximum production of antifungal substance. When ammonium phosphate was added to soil extracts, only a small amount of antifungal substance was produced by E. aerogenes and none by B. subtilis. These results indicate that E. aerogenes and B. subtilis need N and P fertilization of the sterilized soil for the maximum production of the antifungal substance that inhibits the growth of P. cactorum. [ABSTRACT FROM AUTHOR]

The effect of host-plant age, environmental humidity and temperature on the development of the wilting disease of Lolium perenne L., caused by Xanthomonas campestris pv. graminis, was examined. Very young plants were more resistant than older ones. Dry and warm conditions favoured the development and expression of the disease symptoms. Losses in yield were observed under several environmental conditions. [ABSTRACT FROM AUTHOR]

A new method is described for the determination of the total molecular weight of haploid genome DNA. It is based on initial optical renaturation rate measurements of precisely known concentrations of fragmented DNA. The theoretical basis of the measurement is presented. The actual state of replication of the genome has little effect. The exact conditions and the effects of DNA concentration, renaturation time, size of DNA fragments, buffer concentration, optimal temperature and % (G + C) have been determined. Several types of bacterial DNA of known genome size were included as a control. As an application, the DNA genome size have been determined of 40 different bacteria. The method appears to offer advantages by its simplicity, rapidity and reproducibility. [ABSTRACT FROM AUTHOR]

Five bacterial isolates were obtained in a nursery near Gent (Belgium) from diseased Dieffenbachia maculata (Lodd.) G. Don. cv. Compacta, cv. Camillo and cv. Veerle plants. They were identified by API 20E, API 50 CHE and API ZYM systems as Erwinia chrysanthemi. These strains and seven collection strains were pathogenic to all three D. maculata cultivars tested: cv. Camillo, cv. Compacta and cv. Tropic Snow. Inoculation in the stem or petiole was the only effective method for obtaining systemic infection. The petiole appeared to be the part of the plant in which disease developed most readily. Wounding was required for the induction of the disease. Temperatures between 25° and 30°C, a relative air humidity of 75 % or more and low light intensity (0.5 ft-c) favoured the disease, whereas high inoculum sizes (106 or more cells) accelerated and increased it. Histological studies showed tissue degradation in infected areas. Petioles were most severely affected. Transport of bacteria seemed to occur after vessel infection in stem or petiole tissues. [ABSTRACT FROM AUTHOR]