Cucumber black root rot caused by Phomopsis sclerotioides

Phomopsis sclerotioides was proved to be a primary parasite attacking cucumber roots. Black pseudosclerotial and pseudostromatal lesions occurred more commonly at temperatures of c. 20 ^oC but at 10 ^oC unspecific light brown lesions predominated. Damage done by P. sclerotioides was minimal at soil temperatures of c. 20 ^oC, the aerial dry weights of parasitized plants, as percentages of those of the healthy controls, changing from c. 15% to c. 95% as soil temperatures increased from 12 to 20 ^oC. Root lesions were associated with root loss and decreased shoot growth. Severe attacks on young plants resulted in stunted growth and small, intensely green leaves. With less severe or later attacks, growth was initially indistinguishable from that of plants growing in uninfested soils until the rate of leaf senescence suddenly increased; these foliar symptoms temporarily simulated attack by vascular wilt fungi. Both sets of foliar symptoms were associated with appreciable yield losses.