49 Pathogenicity test indicated that tomato seeds only germinated on the non
pathogenic colonies one explanation is given by Sinclair Cerkauskas 1996 stating that endophytes cannot be considered to cause disease, however, genera
and species that can cause disease are regularly isolated and identified as pathogens.
4.2.2 Colonisation Test
Ability of endophytic fungi to colonise plant tissues is an important factor in suppressing the disease incidence in plants. Endophytic fungi with the ability to
colonise plant tissues and develop faster are able to compete with the other microorganisms, making them better antagonistic agents for biological control
activities in plants. Root colonization is the proliferation of microorganisms in, on and around the growing roots. For many microorganisms the zone they occupy
is a function of the root age. Colonisation begins with the dispersal phase, which can result either from growth or movement of the microorganism towards the root,
or from contact by a stationary propagule by a growing root, this is followed by growth phase in which the organism multiplies or grows.
Percentage re-isolation indicated that colonization rate was higher in; isolate XP9, Trichoderma pseudokoningii, Trichoderma hamatum, Nigrospora sp
Fusarium oxysporum and Fusarium chlamydosporum by 100 Table 2. Other
publications have demonstrated that endophytic fungi infect and complete their life cycles in plants asymptomatically Sinclair Cerkaukas 1996. Also in
relation to colonization test, Petrini 1986, 1991 demonstrated that growth of fungal hyphae outwardly from internal tissues of surface sterilized plant tissues is
considered main evidence of endophytism. Ability of endophytic fungi to colonise and develop within the plant tissues forms a very important factor in biological
control of plant diseases. Endophytic fungi with the ability to colonize plant tissues faster, faster culture development and posses the ability to compete with
other microorganisms can form potential antagonistic agent to control and reduce plant diseases.
50
4.2.3 Antagonistic Effect of Endophytic Fungi against RKN In-planta
All the endophytic fungi isolates showed high significant effect in suppression of the number of root galls and egg mass formation. Root galls were
completely suppressed by Nigrospora sp, Trichoderma pseudokoningii, isolate XP9, Trichoderma hamatum, Chrysosporium sp and Fusarium oxysporum. It was
observed that number of root gall and egg masses were very high in tomato plants treated with nematodes only negative control Table 3. Experiments conducted
by Pathan et al. 2004 and Roberts May 1986 indicated greater number of females, galls and eggs per plant in susceptible cultivars inoculated with M.
incognita as compared to moderately resistant cultivars.
According to Tan Zhou 2001 production of bioactive compounds by endophytes may facilitate domination of biological niche within the host plant or
provide protection to the plant. In relation to findings in this research Caroll 1988 and Clay 1988 determined that the association between
endophytic fungi and host plants increases the plant resistance to most pathogens. Niere 2001 also showed that endophyte treated plants had lower total number of
nematode densities. Research findings by Bailey et al. 2006 also supported these results by demonstrating that endophytic Trichoderma sp are able to induce some
genes implicated in plant responses to abiotic and biotic stresses in cacao. The potential for endophytes to provide control of RKN is supported by the
observation that many endophytes antagonize RKN in planta. Via greenhouse experiments, endophytes were successfully introduced into healthy plant tissues,
endophyte-colonized tissues remained asymptomatic and were more resistant to damage and loss due to RKN than were endophyte-free tomato plants. According
to Fallas et al. 1995 shoot and root weight reduction are useful indicators of nematode pathogenicity and may be used to assess suppression of RKN by
endophytic fungi. Kopcke et al. 2002a; Kopcke et al. 2002b reported the production of pregaliellalactone and other related lactones by non-graminaceous
endophytes, which had nematicidal activity. Endophytic fungi are known to produce toxins and other metabolic
compounds that suppress pathogens in the host plant Clay 1988. Niere 2001 also reported that endophyte treated plants had lowered densities of nematodes
51 females subsequently resulting to lower total nematode densities in the plants.
Other examples of production of toxic metabolites by endophytic fungi have also been reported by Ma et al. 2004 that production of rhizoctonic acid and
momomethylsulochrin, ergosterol and 3 β, 5α, 6β-trihydroxyergosta-7.22-dien by
an endophytic isolate of Rhizoctonia sp. An in vitro experiment was conducted earlier in this research to show the mechanism of antibiosis by the endophytic
fungi against root-knot nematodes as indicated in Table 12.
4.2.4 Effect of Endophytic Fungi on Plant Growth
