Age of yield stabilization and its implications for optimising selection and shortening breeding cycle in rubber (Hevea brasiliensis Muell. Arg.)

With the objective to explore the possibility of optimising selection for reducing the number of years of yield recording that could be sufficient enough to establish the lowest risk tapping-age for selecting the potential clones from field-level clone trials, long-term yield data (13-16 years) from eight clone evaluation trials were subjected to formal graphical/statistical analytical techniques. Non-linear curves were fitted to yield data and the year of start of upper asymptotic phase was worked out. Correlations were worked out between mean yield of all the years' data and cumulative mean yield over 3-10 years of tapping. Success rate achieved in the selection of high yielding clones from the third year of tapping was worked out. The mean maximum dy/dx (first derivative of the curve) across all trials ranged from 3 to 7 years of tapping with mean maximum dy/dx at 4 years. Correlations observed from the sixth year of tapping were highly significant in most of the trials. Considering the results from all the three analytical techniques, it was concluded that six years of yield recording would be required for optimising selection of top yielding clones from large-scale clone trials. The possible use of these results is discussed in the framework of a global selection scheme with a view to shorten the breeding cycle of Hevea brasiliensis.