Inheritance of resistance to foot and root rot caused by Phytophthora nicotianae v. Breda de Haan var. nicotianae in tomato (LycopersiconMill.).
SummaryDifferent levels of resistance to foot and root rot caused by P. nicotianae var. nicotianae were found, with the highest level in four American lines. The resistance of these lines depends on one incompletely dominant major gene.
Virulence of Spanish Phytophthora nicotianae isolates towards Capsicum annuum germplasm and pathogenicity towards Lycopersicum esculentum
The virulence of six northwestern Spanish Phytophthora nicotianae Breda de Haan isolates towards the pepper (Capsicum annuum) cultivars commonly used for the determination of P. capsici Leonian pathotype (SCM 334, PI201234 and Yolo Wonder), was similar to that of the latter oomycete but different to that of the German reference isolate P. nicotianae 411.87. When nine local C. annuum cultivars were inoculated with a P. nicotianae isolate of well known pathogenicity, the virulence recorded was significantly different to that recorded for P. capsici. Though the average level of resistance of the northwestern Spanish Capsicum germplasm to P. nicotianae was incomplete and weaker than that recorded for the SCM 334 and PI201234 cultivars, genotypes Co 12B and Co 3.25 showed high resistance to this oomycete. None of the six northwestern Spanish P. nicotianae isolates tested were pathogenic towards Lycopersicum esculentum cv. S. Pedro, unlike P. capsici, which produced clear collar and root rot in this host.
The infectivity of soils containing Phytophthora infestans
Infectivity of soil was measured by incubating samples on potato tuber slices during and after outbreaks of potato blight in three years. Surface soil was always more infective than deeper soil, the most infective surface soil containing the equivalent of 2100 sporangia of P. infestans per ml. Infectivity usually diminished rapidly with increasing depth, and only occasionally did infectivity below 2 in. exceed the equivalent of 100 sporangia per ml. Exceptionally large infectivity was once found at all depths sampled after heavy rain, but rain did not consistently affect infectivity. The surface soil remained infective for at least 32 days after the haulm was killed with acid, but the concentration of viable spores declined to a small value during the first week after treatment. In the laboratory infectivity persisted for 11 weeks after sporangia were mixed with unsterilized soil originally with a moisture content of 20%. P. infestans mycelium grew only in sterilized soils, perhaps because some soil micro‐organisms inhibit its growth, and others (e.g. Trichoderma viride) parasitize it or lyse it (e.g. by Rhizoctonia solani). The three soils tested all contained substances that inhibit the germination of sporangia. 
RESP-5297