Variation in Yield Among Competing Individuals within Mixed Genotype Stands of Tea: A Selection Problem

Abstract

(1) The yields of individual tea bushes within mixed-genotype commercial stands are poorly correlated with their yields when cloned and grown in pure stands. It is proposed that non-genetic inter-plant competition and environmental heterogeneity mask inherent differences in yield in mixed stands, and that improved selection methods can be devised to allow for these non-genetic sources of variation. (2) Inter-plant competition was shown to affect bush plucking table areas, because bushes with large and small plucking table area were evenly dispersed (Ford 1975). There were also negative relationships between plucking table area and the summed areas of adjacent bushes, and correspondingly negative values of a competition coefficient (see Appendix). By contrast, local site differences were indicated by clumps of bushes with large yields per unit area. (3) Spatial analyses suggested that competition was confined mostly to immediate orthogonal neighbours, at 1.2 m square planting, whereas heterogeneity in soil factors, affecting yield per unit area, extended to diagonal neighbours. Bushes with strongly inherited leaf colours occurred at random, and it was expected that bushes with any specified genetic trait, including an ability to produce high-yielding clones would also be randomly dispersed. An attempt to locate such bushes is described.