A New Race of Fusarium Oxysporum f. sp.:Lycopersici Inducing Root Rot of Tomato

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A root and crown rot of tomato caused by Fusarium oxysporum SCHLECHT.(SNYD. & HANS.), different from the ordinary wilt in its symptoms, has been found in several districts of Japan in recent years. This disease occurs in vinyl green houses in winter, but not in warmer seasons. Diseased plants are stunted and chlorotic, then wilt and die. The whole root system exhibits a dry brown rot of the cortex and xylem. Necrosis of the cortex in the stem may develop at or under the soil line. Browning of vascular bundles in the stem rarely develops more than ten cm above the soil level. These symptoms are observed both in the field and in inoculated plants. Isolates of F. oxysporum from these diseased plants were examined for their pathogenicity to twenty-two species of vegetable crops belonging to the Solanaceae, Cucurbitaceae, Cruciferae, Leguminosae, and certain other families. They were not pathogenic at all to crops other than the Solanaceae. Among solaneceous crops, the tomato was severely affected and exhibited the above-mentioned symtoms. Eggplant and pepper were slightly affected by a few isolates. As they are mainly pathogenic to the tomato, they are considered to belong to f. sp. lycopersici. These isolates were also examined for their pathogenicity to tomato varieties. They were pathogenic to all of the tested varieties, that is, Ponderosa and two other varieties susceptible to f. sp. lycopersici races J1 and J2, Okitsu 3 and three other varieties resistant to race J1 and susceptible to race J2, and Walter, resistant to both race 1 and 2 (American differential system). These reactions were different from those either race J1 or J2, the races so far known in Japan. The optimum temperature for the growth of these isolates was estimated at 27-28°C, being similar to the races J1 and J2. On the other hand, the optimum temperature for the disease development was 10-20°C, being apparently lower than that for the wilt caused by race J1 or J2. On the basis of the above-mentioned results, it was proposed to add Walter to the Japanese differential system as a new diffrential variety, and to set up a new race of f. sp. lycopersici, race J3, which is pathogenic to all the three differential varieties. The isolates from the newly found root and crown rot of tomato fell into the new race.
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A New Race of <I>Fusarium Oxysporum</I> f. sp.:<I>Lycopersici</I> Inducing Root Rot of Tomato

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