Transmission Characteristics of the Clover Phyllody Agent by Dodder

The results obtained in investigations on the biological characteristics of the clover phyllody agent (CPA) in respect to its transmission by the experimental vector Cuscuta campestris Younk, using Catbarantus roseus L. as constant host, are reported. Transmission efficiency of CPA was comparable whether the “stable bridge” or the “cut strand” of dodder method was adopted. The acquisition and inoculation threshold was between 4 and 6 days. The efficiency of transmission became greater by lengthening the test period up to 15 days. In cuttings of dodder maintained in water after recision, the maximum retention of infectivity, in respect to transmission capacity of CPA, was 28 days. It was proved that CPA invades C. campestris in a persistent manner. In comparative tests between CPA and APA (apple proliferation agent) it was demonstrated that the former is more efficiently transmitted than the latter. Moreover there is a much higher pathogenic effect of APA than CPA in dodder; in fact C. campestris as well as C. subinclusa Dur. and Hilg. develops poorly and shows deformations when growing on AP infected periwinkles. The basic distinguishable symptoms of the two diseases in C. roseus are: virescence and phyllody for CP; small but never virescent flowers for AP. MLOs have been detected, by electron microscopy, in sieve elements of C. roseus and C. campestris infected by CPA.