SOME EFFECTS OF NITROGEN SUPPLY ON THE INFECTION OF TOMATO PLANTS WITH TOMATO SPOTTED WILT VIRUS

The susceptibility of tomato plants to systemic infection by tomato spotted wilt virus was increased by increasing nitrogen supply to levels above that optimal for growth. The virus content, estimated by local-lesions counts, was also raised by increasing nitrogen. The period between inoculation and the appearance of systemic symptoms was decreased by increasing nitrogen to a point slightly greater than the optimal level for growth, but increased by additional applications. Infected plants receiving more nitrate or ammonium compounds than were needed for optimal growth showed abnormal leaf symptoms and no bronzing. N, P and Mg analyses showed that these symptoms were related primarily to nitrogen content. Such leaves contained more virus than bronzed leaves.