Under high rainfall and high relative humidity, vanilla can withstand more sunshine than during low humidity and drought periods. Thus, it is important that support trees maintain much of their foliage during dry periods.
Trailing and Pruning
The trailing nature of vanilla vines has an effect on flowering. The vines are coiled around the lower branches of the supporting tree or over the lattice of trellis so that they may hang down. Care is required not to tear or bruise the leaves, branches, or roots. Bending of vines appears to be an important operation for inducing flowering and fruiting beyond the bend, which may be due to accumulation of carbohydrates and possibly other flower-inducing hormones in such regions of the vine.
Arresting the vegetative growth of vanilla vine by pruning helps to induce flowering. Training and pruning are undertaken to induce flowering and bean production. Here, the hanging shoots of 1–1.2 m long are bent down around the branches of the support tree, slightly twisted in the process, with tips pruned at about 45 cm from the soil. Any vegetative shoots appearing after the bend portion of the hanging shoot are removed, but the shoots appearing on the rest of the plant before the bend portion of the hanging shoots are allowed to grow. These shoots will constitute the bearing branches of the following year. As a result, there is a decreased sap flow toward the bearing branches, which favors flower formation. After the harvesting of beans, the yielded portion of the vine is removed from the plant. The following year’s bearing branches are to be prepared by bending and pruning. Plants that have been pruned and readied for flowering require heavy manuring of leaf mold, decomposed leaves, lime, ashes, and manure. The vine architecture after 3–4 years is therefore of vine with a number of shoots hanging down over the branches of the live support, without overcrowding or overlapping. Normally, five to six bearing branches per plant can be prepared per annum, depending on the age and growth of the vine.
The yielding behavior of pruned hanging shoots under different growth stages comprising of 4, 6, 8, 10, and 12 nodes per shoot was studied. It revealed that the formation of inflorescence is irregular in the hanging shoots irrespective of its growth stage. The 10-node hanging shoots had maximum number of inflorescences per shoot. However, the first-grade quality of beans (above 15 cm) was 57% in 10-node shoots, 77% in 6-node, and 88% in 4-node hanging shoots, respectively, indicating that production of more number of beans in a bunch or in a productive vine would be at the expense of size of the beans (Hrideek et al., 2003).
When the pods are ripe and harvest is completed, the yielded portion of the vine is removed and only the new shoots of the previous year are retained. Plants that have been pruned and readied for flowering require heavy manuring of leaf molds, rotting leaves, lime, ashes, and cow dung.
Diseases and Their Management
Fungal and viral diseases are the main production constraints. The crop losses due to these biotic stresses vary. Fungal diseases such as Fusarium and Phytophthora rots cause severe crop losses, and occasionally total crop losses are reported. The viral diseases, although not lethal, result in varying degrees of production and productivity losses. Vanilla being an exotic plant for India, the planting material might have come from outside unknown sources where the virus-free nature of the material was never ascertained and quarantine regulation was never applied. Lack of adequate molecular diagnostic facilities, especially for viral diseases, is another major constrain that limits the detection of viruses. This is important in view of the vegetative propagation method of cultivation. The genetic variability with respect to disease/ pest resistance is comparatively low, which might be the reasons for high disease incidence and consequent crop loss.
Except for the reporting of new diseases, detailed investigations on the management of various diseases are insufficient. Integrated pest and disease management remains an important priority for crop protection of vanilla, with a greater focus on biological control to reduce pesticide inputs for vanilla cultivation.
Vanilla being a crop with poor genetic variability for disease resistance, efforts should be made to induce more variation to identify reasonable disease resistance or tolerance for the major diseases. The recent report of variable disease reaction in seedling progenies of vanilla and somaclonal variations is of considerable interest and needs to be pursued further (Minoo et al., 2006b).
The main diseases reported on vanilla in India are given in Table 20.3.
| Name | Causal Agent | References |
|---|---|---|
| 1. Fungal | ||
| Major: | ||
| 1. Stem, root rot, and wilt F. oxysporum sp. vanillae Philip (1980), Joseph Thomas et al. (2003) | ||
| 2. Phytophthora leaf, stem blight, and bean rot P. meadii Bhai and Thomas (2000) | ||
| Minor: | ||
| 3. Immature bean yellowing and shedding | C. vanillae | Thomas et al. (2003) |
| 4. Bean rot | Sclerotium rolfsii | Thomas and Bhai (2000) |
| 5. Brown spot | C. quinquiseptatum | Bhai et al. (2006) |
| 6. Shoot tip rot | C. gloesporides | Thomas et al. (2003) |
| 2. Viral | ||
| 1. Mosaic | CMV—Cucumovirus | Madhubala et al. (2005) |
| 2. Mosaic and stem necrosis | Potexvirus, potyvirus, and closterovirus | Bhat et al. (2004) |