Exogenous Cellulase Contributes to Mycoherbicidal Activity of Fusarium arthrosporioides on Orobanche aegyptiaca

This paper investigates an association between the tubercle size of Orobanche aegyptiaca, tubercle death, and days to tubercle death in relation to cellulase-assisted mycoherbicide. Fusarium arthrosporioides killed 56% of tubercles when applied with cellulase compared to 35% when no cellulase was added. Death was inversely correlated with days over the two fungal treatment types. O. aegyptiaca tubercle size significantly correlated with the two other infection parameters studied. For F. arthrosporioides, only 9% ( ) of the variation in days to death was explained by variation in tubercle size, whereas with cellulase it reaches 14%. In this study, mycelia of F. arthrosporioides did not show apparent damage to the tomato roots. 1. Introduction Orobanche spp. (broomrapes) are holoparasitic flowering plants, penetrating roots of susceptible hosts, removing water, minerals, and sugars. Orobanche attacks several crops causing enormous yield losses [1]. Orobanche generally maintains a close relationship with the host and so it is unreasonable to attack it using herbicides because the latter may adversely affect the nontarget host. Despite research on Orobanche spp. for over three decades, yield losses still abound because there is no sustainable method for controlling the parasite. Several weed biocontrol agents are not sufficiently virulent for field release [2]. Since hydrolytic enzyme plays an important role in the pathogenicity of plants by facilitating fungal penetration through the host cell wall [3, 4], it may be worthwhile to attempt coinoculation of enzyme and fungi. A series of experiments were conducted using Fusarium arthrosporioides, a biological control agent that infects Orobanche without affecting the roots of tomato. Experiments using mycoherbicidal organisms plus pectinase enzyme [5] indicate that the enzymes enhance the weed control of a pathogenic fungus. The role of cellulase for plant pertains to modifing cellulose assemblies that are the dominant component of the plant cell wall [6]. Here, cellulase has been used to improve the virulence of F. arthrosporioides on tomato plants infested with O. aegyptiaca. A semiaxenic polyethylene bag system was used that allowed easy visual observation of the fungal infection of the tubercles. It was demonstrated that O. aegyptiaca tubercle size best described the relationship between tubercle death and biological control treatment. The addition of cellulase alone or in mixtures enhanced the virulence of F. arthrosporioides on O. aegyptiaca. 2. Materials and Methods 2.1. Fungal Inoculum Production F.