Studies are currently being conducted on the genetic diversity and population structure of F. oxysporum f. sp. vanillae throughout Indonesia, including reference isolates from various parts of the world. These include the use of PCR-based fingerprinting markers as well as phylogenetic analysis of multiple gene regions. Preliminary results indicate the presence of a relatively high number of haplotypes, some of which form large clonal groups. The 87 strains of F. oxysporum f. sp. vanillae isolated in China (Xia-Hong, 2007) belonged to 12 different VCGs with no correlation between VCG and virulence.
The isolation of nonpathogenic strains of F. oxysporum from vanilla roots led to investigations on the possibility of utilizing some of these strains as biocontrol agents against Fusarium rot of vanilla. Promising results have been observed under experimental conditions, but field efficacy has yet to be verified.
Control Measures
Although several vanilla relatives, such as Vanilla phaeantha, Vanilla aphylla, and Vanilla andamanica, have been shown to be resistant to Fusarium rot (Theis and Jiménez, 1957; Minoo et al., 2008), commercial varieties resistant or tolerant to Fusarium rot have not yet been described. Owing to the fact that Fusarium rot can infect various plant parts at all stages of growth, integrated control measures against this disease are paramount and should be implemented right from the cutting preparation stage, throughout the vegetative and productive phases in the field, until senescence (Hadisutrisno, 1996; Tombe et al., 1997; Anandaraj et al., 2005; Tombe, 2008). Several components of reported control measures among others are the application of benomyl, carbendazim, and mancozeb fungicides (Matsumoto et al., 1992; Anandaraj et al., 2005; Bhai et al., 2006), and biological agents such as Bacillus sp., Pseudomonas fluorescens, and avirulent strains of F. oxysporum (Tombe et al., 1992c, 1997; Hadisutrisno, 1996; Anilkumar, 2004).
Integrated control measures have been developed in Indonesia, which involve the use of (a) pathogen-free and disease-tolerant cuttings inoculated with a nonpatho-genic F. oxysporum strain 10A–M (Figure 8.3) to induce resistance (Bio-FOB cuttings), (b) fungicides, such as benomyl or mancozeb, by dipping cuttings for 20–30 min, (c) biological agents Trichoderma lactae and Bacillus pantothenticus (Figure 8.3), Bacillus firmus and T. lactae or P. fluorescens (Tombe, 2008) premixed with organic material, and (d) botanical fungicide eugenol extracted from clove leaves or clove fruit stalks. Table 8.1 outlines the recommendations for the control of Fusarium rot of vanilla in various scenarios based on an integrated disease management (IDM) approach in Indonesia.
FIGURE 8.3 Biological agents used in the integrated control of Fusarium rot in Indonesia: (a) approximately 3-month-old vanilla cuttings treated with nonpathogenic Fusarium oxysporum strain 10A–M; (b) antagonistic test of B. pantothenticus to F. oxysporum f. sp. vanillae; (c) B. pantothenticus on sucrose peptone agar; (d) Trichoderma lactae on potato dextrose agar.
| IDM Recommendations | New Plantation | Plantation without Any Disease Symptoms | Plantations with Low Disease Incidence and Mild Severity | Plantations with High Disease Incidence and Severity (before Replanting) |
|---|---|---|---|---|
| Plant pathogen-free cuttings (Bio-FOB) | + | |||
| Dip cuttings with fungicides (benomyl or mancozeb) | + | |||
| Use organic fertilizer amended with biocontrol agents | + | + | + | |
| Apply organic mulch, for example, hay, coconut husks, clove leaves | + | + | + | |
| Follow local recommendations for land tilling, plant spacing, irrigation, and shade trees | + | |||
| Regularly monitor for early symptoms and physically remove any disease tissue. Disinfect cutting tool | + | + | + | |
| Regularly apply botanical or synthetic fungicide, especially after fertilizing, pruning, weeding, and harvesting | + | + | + | |
| Regularly prune shade trees to control humidity and shade | + | + | + | |
| Improve drainage especially during rainy season | + | + | + | |
| Physically remove disease tissue and apply botanical or synthetic fungicide to cut wounds. Disinfect cutting tools | + | + | ||
| Introduce crop rotation with other plants | + | |||
| Completely eradicate diseased plants and implement rigorous sanitation measures | + | |||
| Plough land thoroughly to improve soil solarization | + | |||
| Grow annual crops such as corn and beans as well as crops believed to maintain antagonistic microorganisms (e.g., Welsh and red onion, Chinese chive, garlic) | + |