. Introduction
Fusarium wilt is a worldwide soil-borne disease, which is
caused byFusarium oxysporumSchl. It is also the most serious
disease on watermelon, muskmelon, cucumber, wax gourd and
other melons which has caused huge economic losses by threat-ening crop production. However, exceptions to the concept of
formae specials have been reported in these formae specials
(Chalfie et al., 1994). On the basis of the cross-infectivity of
these formae specials, the genetic relationships within and
among these formae specials have been questioned.
Green fluorescent protein (GFP) is a small protein found in
the jellyfish Aequorea victoria. It has the property of fluoresc-ing when excited by UV light (Chalfie et al., 1994). GFP-marked strains of Pseudomonas Green fluorescent protein
(GFP) expression is now a widely used tool in the molecular
analysis of filamentous fungi, as reviewed by Lorang
(McMillan, 1986). This inert reporter is excited by UV light
(395 nm) and emits green light (509 nm) making it more easily
visualized using epifluorescence microscopy employing com-monly available filter sets. GFP has the additional advantage
in that it does not require a substrate, eliminating associated
solubility, toxicity, or permeability problems. The GFP marker
has been introduced intoRhizobium melilotiandRhizobium
leguminosarum bv. trifolii to visualize the tagged bacteria in
the rhizosphere and on root surfaces (Gage et al., 1996; Prayitno
et al., 1999). Most of these fungi have been ascomycetes, with