Plantation Crops

Polyclonal seedlings in rubber

All desirable characters viz., high latex content, drought resistance etc may not be available in a single clone. Hence, it may not be wise to adopt a single clone for cultivation in large areas, because if disease or pest epidemic occurs the entire plantation may be wiped out.
Therefore to get the benefits of mixed clones in a population, poly clonal seed gardens are being established by blending different clones. The hybrid RRII –105, is the highest yielding in the world. It has become very popular, occupying 80 per cent of the area under rubber.
Its average yield is 2.400 kg /ha/year. Superior clones numbering 3 to 6 are planted in an isolated area and allowed for natural open pollination. For prevention of pollen contamination from rubber trees of neighbouring area an isolation belt of 100 m width is provided all around the seed plantation.
Polyclonal seed families generally give rise to seedlings of good vigour and growth. In olden days monoclonal seeds of single selected mother clones such as Tjir –1, not contaminated by crossing with seedling rubber or undesirable male parent clones had been extensively used as improved plant materials.
Poly clonal seeds are easier to establish and maintain when compared to buddings. The trunk of the seedlings are much larger than those of budded trees.

Sl No.	Features	Polyclonal seeds	Buddings
1.	Establishment and maintenance	Easier	Comparatively needs more care
2.	Trunk size	Larger	Comparatively of less diameter
3.	Susceptibility to wind damage and diseases	Less	More
4.	General yield level	Low (1200 to 1300 kg /ha/year)	High ( 1200 to 1700 kg per ha per year)

Table: Differences between polyclonal seeds and buddings of rubber

General yield levels of polyclonal seedlings are much lower than selected modern clones ( buddings). However, selection based on initial vigour, high initial planting density in the main field and subsequent judicious thinning of weaklings and poor yielders in a phased manner is suggested to maintain the higher level of productivity.