Factors Affecting the Infection of Plants with Clover Phyllody Agent Transmitted by Macrosteles fascifrons1

Abstract

Transmission of the clover phyllody agent (CPA) by female aster leafhoppers, Macrosteles fascifrons(Stål), was increased from 11 to 89% by increasing the inoculation access periods on aster seedlings from one hour to 7 days. No transmission was obtained with 0.5 hour feeds. When inoculative leafhoppers were given one-day inoculation access feeds on several species of plants, percentage transmission ranged from 10% for Potentilla intermedia L. to 100% for Thlaspi arvense L. The percentage of plants that developed symptoms varied with site of inoculation. New leaves were the most efficient site (49%), followed by the upper surface of the middle leaf (34%), lower surface of middle leaf (26%), old leaf (23%), and basal portion of main stem (9%). Two-week-old asters were more susceptible (87%) than were 4- (46%), 7- (72%), or 9- (65%) week-old plants. Female leafhoppers were considerably more efficient transmitters than were males when compared at inoculation access times ranging from one to 48 hours. The average incubation period in plants inoculated by females (23.1 clays) was shorter than in plants inoculated by males (27.6 days). Movement of CPA from its inoculation site in a leaf to the main stem of the plant occurred in periods ranging from less than 8 hours to more than 48 hours. All attempts to transmit CPA through eggs laid by inoculative M. fascifrons failed.