Pathogenicity of «Phytophthora nicotianae» Isolates to Tobacco and Tomato Cultivars

Sixty-one isolates of Phytophthora nicotianae were tested for pathogenicity to tobacco and tomato. All the isolates but one from tobacco were pathogenic to tobacco but none of the isolates from tobacco were pathogenic to tomato. Of the 53 isolates from non tobacco hosts, 19 proved pathogenic to tomato. Seven isolates from different non tobacco hosts colonized the tobacco stem and produced necrosis but not black shank. Five isolates colonized the tomato stem without causing disease symptoms. Tobacco cultivars BX 2a and KP 14/a were susceptible to isolate BPIC 1921. Tomato cv. Early Pak was susceptible to isolate BPIC 1932 and the Tondino cv. was susceptible to isolate BPIC 1933. No isolate was virulent on both tobacco and tomato. Our results showed that the black-shank isolates of P. nicotianae are a separate group with a specific pathogenicity to tobacco plants only and that prolonged growth in colture may or may not produce loss of virulence - pathogenicity