Tissue specific reactions of sorghum roots to the mycoherbicide Fusarium oxysporum f. sp. strigae versus the pathogenic F. proliferatum

Publikations-Art

Zeitschriftenbeitrag (peer-reviewed)

Autoren

Ndambi, B., Cadisch, G., Elzein, A., Heller, A.

Erscheinungsjahr

2012

Veröffentlicht in

Biocontrol Science and Technology

Band/Volume

22/

Seite (von - bis)

135-150

Abstract

Fusarium oxysporum f. sp. strigae (Foxy 2) is a mycoherbicide against Striga
hermonthica. To ensure the safe use of this biocontrol agent, and as part of the risk
assessment, this study was aimed at providing cytological evidence that Foxy 2
15 does not possess pathogenic behavior towards the non-target host sorghum.
Therefore, we compared the infection processes and sorghum root tissue reactions
towards the pathogenic F. proliferatum to that of Foxy 2 using light- and
transmission electron microscopy. Given that during the growth process, hyphae
could get into the central cylinder, tissue specific reactions of sorghum to Foxy 2
20 were also investigated by wounding the roots (exposing the vascular system), and
testing for proliferation of hyphae within the vessels. Results showed that 2 weeks
after sowing, F. proliferatum had invaded and destroyed all cell types including
the central cylinder while Foxy 2 hyphae were located around the outer
endodermal layer and were not able to penetrate the latter. There was an increase
25 in blue autoflourescence in the central cylinder and especially the endodermis,
probably due to increased phenolics in Foxy 2 infected roots which was not the
case for F. proliferatum. This might contribute to the inability of Foxy 2 to
penetrate the endodermis. Transmission electron microscopy showed extensive
degradation of endodermis and vessel walls into thin translucent layers by
30 F. proliferatum but not by Foxy 2. In the mechanically wounded and infected
roots, Foxy 2 could invade the central cylinder close to the wound but was not
identified a few millimeters away from the wound. This implies that it was not able
to grow within or destroy the central cylinder even when already present within it;
probably due to the observed increased phenolics. Thus, exposure of the vascular
35 system did not serve as a route for the invasion of Foxy 2 which therefore could
not further cause tracheomycosis. Therefore, Foxy 2 could be seen as a fungus
well suited for biocontrol.