Brown-blotted root rot of carrots in Japan. 1. Occurrence, symptoms and isolation.

Abstract

Blot-like lesions have occurred on taproots of carrots in summer-and winter-maturing crops in Chiba Prefecture for past 10 years, resulting in significant quality and yield losses. Pythium sulcatum (ref. (2) in the same title) was isolated from these diseased roots in various localities of Chiba Pref. The disease was severe in the fields with repeated cultivation of carrots, especially in the years with excessive rainfall prior to the harvest. The fungus was only pathogenic to the roots of carrots, but it did not cause damping-off nor leaf blight. In the summer-maturing crop, water-soaked brown circular or elliptical lesions, 3-5mm in diam, were formed mainly on taproots at harvest, and often soft-rotted on the surface. In the winter-maturing crop, small brown slightly sunken spots, 2-3mm in diam., accompanied occasionally with vertical cracks were formed on the taproots. In both cropping types, lateral roots were discolored to brown and decayed frequently and these roots got off from the taproots. Variations of the symptoms may be due to differences of cultivars, time of the disease occurrence and soil conditions.