Research on the methods of producing zoosporangia and inoculation of Phytophthora parasitica var. nicotianae Pathogenicity differentiation of Phytophthom parasitica and the disease resistance difference of tobacco against black shank Construction and Analysis of Tobacco SSH Library Induced by Phytophthora parasitica var. nicotianae The physiological and biochemical understanding of the inhibitory effect of endophyte Itb57 on Phytophthora parasitica var. nicotianae