H. Thomas et al., THE POTENTIAL OF FUSARIUM-OXYSPORUM F-SP ORTHOCERAS AS A BIOLOGICAL-CONTROL AGENT FOR OROBANCHE CUMANA IN SUNFLOWER, Biological control (Print), 13(1), 1998, pp. 41-48
Fusarium oxysporum Schlecht. f.sp. orthoceras (Appel & Wollenw.) Bilay
was evaluated for its potential to control the root-parasitic weed Or
obanche cumana Wallr. The effectiveness of conidial inoculum of this s
oil-borne fungus was determined in pots and root chamber trials with t
he host-parasite association sunflower (Helianthus annuus L.)/O. cuman
a. Conidia applied postemergence infected emerged parasite shoots befo
re they reached their flowering stage and produced seeds. The high lev
el of virulence of the fungus was proven by efficient Orobanche contro
l at low inoculum doses. The preplant application of 10(4) unformulate
d conidia at a density of 69 conidia/cm(2), which were incorporated in
to 1 kg of soil, resulted in significant disease incidence on O. cuman
a shoots as well as a reduced rate of emergence. The strong suppressio
n of broomrape development after soil incorporation of higher doses of
conidia led to 89% increase in dry matter of sunflower, compared to t
he fungus-free control. Effective control by O. cumana was due to the
susceptibility of early underground developmental stages to the pathog
en. The mortality of tubercles increased significantly to 85% after in
oculation with the fungus. The number of parasitic attachments on sunf
lower roots was reduced due to mortality of the seed's germ tube. In a
ddition, suppression of seed germination was observed. Hence, each dev
elopmental stage of O. cumana represents a potential target for F. oxy
sporum f.sp. orthoceras attack. Orobanche cernua Loefl. grown on tobac
co (Nicotiana tabacum L.) was also susceptible to the pathogen. In con
trast, biotypes of O. aegyptiaca Pers. on tomato (Lycopersicon esculen
tum Mill.) are nonhosts of the fungus. (C) 1998 Academic Press.