Evaluation of Systemic Resistance to Blue Mold Induced in Tobacco Leaves by Prior Stem Inoculation withPeronospora hyoscyamif. sp.tabacina

Abstract

Conidia of P. hyoscyami f.sp. tabacina (which causes blue mold of tobacco) applied to the stem-root interface zone of potted burley tobacco plants induced systemic protection of the foliage against the blue mold disease caused by the same pathogen. Neither heat-killed or sonicated conidia of P. hyoscyami f.sp. tabacina nor untreated inocula of 3 other tobacco pathogens or 3 nonpathogens induced protection against blue mold. Protection was associated with the necrosis that developed in the external phloem and cambium of the stem subsequent to the initial inoculation with P. hyoscyami f.sp. tabacina. Approximately 2 wk was required for development of .apprx. 50% protection and 3 wk for .apprx. 95%. Resistance in the leaves of protected plants was not confined to the epidermis; conidia infiltrated into leaf panels to produce normal lesions.