INTERACTIONS BETWEEN RACES OF FUSARIUM OXYSPORUM F.SP. DIANTHI AND CULTIVARS OF CARNATION

In two experiments the virulence pattern of races 1, 2 and 4 of Fusarium oxysporum f.sp. dianthi was investigated in relation to carnation cultivars. The results show cultivar x race interactions, but also some differentiation between isolates of a race.

Isolates of race 2 induced regular Fusarium wilt symptoms in most cultivars. At the end of the test period, only the cultivars Revada and Novada remained externally symptomless.

Histopathological investigations of some cultivars showed a heavy degradation of cell walls and xylem parenchyma cells, with dark brown discoloration of the surrounding tissue.

Isolates of race 4 induced similar, but less aggressive symptoms. However, some interactions were found: Lena was less susceptible to race 4 than to race 2, but Pallas, Alice and Sam's Pride showed severe or complete wilting.

The pathogenesis of race 4 isolates was similar to that of race 2, with less vascular browning.

Race 1 induced atypical Fusarium symptoms in some cultivars. Most of them remained resistant, but Niky, Elsy and Sam's Pride showed a rapid necrosis of leaves, followed by wilting. The vessels of these cultivars had assumed a pale brown colour and were colonized heavily. However, no degradation of cell walls was observed.