Tomato plants grown in a Fusarium wilt suppressive soil and in the same soil steamed and amended with non-pathogenic Fusarium strains were protected from subsequent infection with Fusarium oxysporum f. sp. lycopersici.Protected plants had higher laminarinase, chitinase, N-acetyl-glucosaminidase and /3-l,4glucosidase activity than unprotected plants grown in steamed unamended soil. Higher peroxidase and polyphenoloxidase activity and higher content of phenols were also associated with suppressive soil conditions, although in a less consistent way.Among 5 non-pathogenic Fusarium strains, strain Sal was the most suppressive and enhanced enzyme activity more than did the other strains, whereas strain T was inactive and did not induce changes in activity.These results are in accordance with previous work showing that induced resistance is associated with enhanced activity of glycosidases and phenol oxidizing enzymes, and increased phenols content. It is suggested that induced resistance is part of the mechanism of the natural suppressiveness of soil and that this resistance is induced by non-pathogenic Fusarium strains. ' ZusammenfassungPhysiologische Reaktionen von in Fusarium suppressiven Boden wachsenden Tomatenpflanzen Tomatenpflanzen, die in einem Fusarium-^e\^e suppressiven Boden bzw. in dem gleichen mit Wasserdampf sterilisierten und anschliefiend mit nicht pathogenen FusariumSt'immen inokulierten Boden wuchsen, wurden von einer Infektion durch Fusarium oxysporum f. sp. lycoperski geschiitzt.

The influence of some chemical and physical factors (pH, temperature and light) on degradation (hydrolysis) and volatilisation of methyl bromide (MB) from natural fresh waters was investigated. The complexity of the processes involved in MB persistence was shown. Under static and air‐free conditions the half‐life is quite long (30‐50 days) but is decreased by an increase in pH and temperature (9‐10 days), by UV irradiation (10‐12 days) and, most of all, by exposure to air and shaking of the solution (2 h) and by soil.

Changes of P-l,3-glucanase, chitinase, P-l,4-glucosidase and N-acetylglucosaminidase activity have been investigated in relation to the development of symptoms and colonization by the pathogen in roots, stems and leaves of susceptible ('Improved Pearson') and resistant ('Improved Pearson VFir) tomato plants infected by Fusarium oxysporum f. sp. lycopersid.Glycosidase activities increased after inoculation to different extents depending on the plant part and cultivar. Increases were always higher in susceptible than in resistant plants. Changes in the P-1,3glucanase activity after inoculation were particularly large in stems of infected plants. In contrast, chitinase activity increased more in roots than in stems.The P-l,3-glucosidase and chitinase activity decreased slightly from the basal to the apical third of stems.The trend of changes of the glycosidase activity generally were well related with the severity of disease symptoms and the fungal colonization of basal stem segments.There was no evidence that the increase of glycosidase activity after the infection was directly related with the resistance to Fusarium wilt in tomato.

No abstract

Salicylate watered onto the soil of tobacco plants in pots reduced the antigen accumulation and local lesion growth of tobacco necrosis virus mechanically inoculated on the leaves. It also retarded the growth of the necrotic centres of lesions and, in parallel, inhibited ethylene production from infected leaves. However, the therapeutic index of salicylate was very small and the chemical had to be applied in advance of, or at the same time as virus inoculation to give good levels of resistance. The number of lesions and their rate of appearance were not affected by salicylate. In addition, it did not induce resistance against multiplication, systemic spread or symptom severity in tobacco plants inoculated with a necrotic strain of potato virus Y. These findings suggest that salicylate is not likely to prove useful as polyvalent chemotherapeutic agent.