Responses related to lignification and intravascular periderm formation in carnations resistant to Fusarium wilt

Abstract

Stem inoculation of resistant 'Novada' carnations with Fusarium oxysporum Schlecht. f.sp. dianthi (Prill. & Del.) Snyder & Hansen, races 1, 2, and 4 or F. oxysporum Schlecht. f.sp. lycopersici (Sacc.) Snyder & Hansen did not induce visible disease symptoms. The plants showed a similar localization response to all fungal isolates. The response consisted of the occlusion of xylem vessels with brown gums, and browning and death of some xylem parenchyma cells, as well as the occurrence of various wall modifications in other xylem parenchyma cells. The wall modifications comprised the deposition of additional wall layers, formation of various appositions, and infusion with phenolic-containing material. The brown gums and infused walls eventually contained phenolic polymers related to lignin. The occluded zone was surrounded by hyperplastic xylem parenchyma tissue, of which the inner cell layers differentiated into suberized phellem tissue, whereas vascular regeneration occurred in the outer layers. The significance of the various wall modifications and of the formation of intravascular wound periderm for resistance of carnations to Fusarium wilt is discussed.