THE POTENTIAL USE OF FLUORESCENT PSEUDOMONADS IN THE PROTECTION OF CARNATIONS AGAINST FUSARIUM WILT IN HYDROPONICS

Pseudomonas putida strain WCS358 and Pseudomonas spp. strains WCS417 and X.13 inhibited mycelial growth of Fusarium oxysporum f. sp. dianthi (F.o.d.) on King's medium B (KB) agar plates. Strain X.13 also inhibited growth of the fungus on KB supplemented with iron and on potato dextrose agar (PDA). This suggests that growth of F.o.d. is inhibited by siderophores as well as antibiotics produced by these pseudomonads.

Germination of microconidia in liquid KB was strongly inhibited by WCS358 and WCS417 (more than 50%), whereas 22% was inhibited by X.13. When F.o.d. was grown in an iron-deficient carnation nutrient solution, enriched with 2% glucose, germination of microconidia was less inhibited than in KB (12–17%).

Rooted cuttings of the susceptible cultivar Lena and the moderately resistant cultivar Pallas, grown in a nutrient film system were inoculated with suspensions of WCS358, WCS417 and X. 13. After 19 weeks, disease incidence of 'Lena' was reduced by WCS417 (13%) compared to that of the non- bacterized controles, while this strain in 'Pallas' postponed disease symptoms for more than 6 weeks. WCS358 and X.13 reduced the numbers of diseased plants in 'Pallas' with 10 and 7%, respectively.