Spore Germination Tests Research Articles

New disease of Tomato (Lycopersicon esculentum Mill.) caused by Cercospora sp.

1. The present paper gives the results of morphological and physiological studies on the causal fungus (Cercospora sp.) of a new disease of tomato.2. The symptoms of the disease closely resemble “leaf mould of tomato (Cladosporium fulvum), ” and it is almost impossible to find the difference between these two diseases except under microscope.3. The present disease is widely distributed in Japan, and causes often serious damage to tomato.4. The causal fungus is almost identical to Cercospora diffusa, ecxepting that the former has septated conidiophores.5. The author proposes a new common name “Cercospora leaf mould” for the present disease.6. Optimum temperature for germination of the conidia is about 26°C, and maximum about 36°C.7. Mycelial growth of the fungus is very poor on common culture media forming minute colonies in island type, and saltation occurs very often.8. Conidial formation is comparatively good on tomato plant decoction agar and optimum temperature for mycelial growth of the fungus seems to lie between 26-28°C and maximum 34-38°C.9. Conidia on tomato leaves kept thier vitality under ordinary conditions in the laboratory until the end of the following June, but they all died after 40 days in moist condition. Therefore conidia may live over winter in natural conditions and cause primary infection in the next season.10. The author made infection experiments of the fungus on tomato seedling with success and reisolated the same fungus from affected leaves.11. Varietal susceptibility of tomato is still unknown, but the author found two resistant varieties “Dwarf Stone” and “Marglove” among 35 varieties in the field.12. According to the spore germination test in vitro, Bordeaux mixture showed the strongest fungicidal power on the fungus, Zerlate and Fermate came next, while wettable sulphur (Soid No.1) was very weak.Postscript:The present fungus was lately identified to Cercospora fuligena Roldan by Dr. CHUPP.

Behaviour of Thiuram Sulphides, etc., in Spore Germination Tests

SOME seven years ago, in the course of sorting tests of potential organic fungicides, it was noticed that tetramethylthiuram monosulphide sometimes gave irregular results. In certain tests an 'inversion' of toxicity occurred, that is, within a limited range of concentration, toxicity to fungus spores (Venturia inæqualis) decreased as the concentration of fungicide increased. When this effect was first observed it was ascribed to some experimental mishap, but it was repeated with sufficient frequency, though not invariably, to convince us that the phenomenon was authentic. It was later seen in the case of tetramethylthiuram disulphide, though not before several tests had been completed without any indication of it, and has been investigated most fully in relation to this compound. Confirmation of the effect has since been provided by the independent observations on the latter substance reported by Dimond et al.1, using spores of Macrosporium sarcinæforme.