Epsilon Open Archive

Abstract

Verticillium wilt is the major disease responsible for yield losses in oilseed crops in Sweden today. V. longisporum is the most prevalent Verticillium pathogen found in Swedish soils, but V. dahliae and V. tricorpus can also be found. Very little data exists concerning the infection pattern, host range and triggered defence responses in plants toward V. longisporum. This thesis aims to extend our knowledge about V. longisporum and its host. The infection process of V. longisporum and V. dahliae in oilseed crops was compared. V. longisporum was found to colonise oilseed crops through lateral roots and root hairs, compared with V. dahliae that colonise via the primary roots. At plant maturation, V. longisporum was found throughout the plant, in roots as well as in stems and leaves. Whereas V. dahliae in 67% of the cases only was present in the root and lower stem. To investigate the host specificity of V. longisporum, seven species, both crops and weeds were inoculated with three isolates (VD2, VD4 and G1-11). Brassica napus, Sinapis arvensis and Matricaria inodora were found to be highly susceptible to the pathogen, but microsclerotia could also be re-isolated from Triticum aestivum and Avena sativa. In Swedish soils the density of microsclerotia ranged from 1 to 48 cfu/g soil, causing between 4 and 72% of disease incidence in the fields. However, no direct correlation could be found between microsclerotia density and disease incidence. A regression analysis showed that the yield of the winter oilseed rape crop could be predicted by using three variables: percentage Verticillium wilt diseased plants, temperature in May and temperature in September. The early plant defence response in Arabidopsis thaliana towards V. longisporum is dependent on ethylene and jasmonic acid. Increased ethylene production is also important for later symptom development, such as wilting and chlorosis. Six mutants were found to be susceptible to V. longisporum: ein4-1, ein2-1, ein6-1, ndr1-1 npr1-1 and rfo1-1. RFO1 is a wall-associated-receptor-like protein, found to confer resistance to V. longisporum similar as earlier found to Fusarium oxysporum.