Selection of sugarcane clones in small plots: effects of plot size and selection criteria

Sugarcane (Saccharum spp.) clones are frequently evaluated in one- or two-row plots in the early stages of selection in sugarcane breeding programs. This study assessed the value of performance in small plots for predicting performance under near pure stands and compared different selection methods and criteria based on measurements made in small plots. Two populations of unselected seedling clones were evaluated in different plot sizes in experiments at two sites over two and three crop-years, respectively. Commercially recoverable sugar content in cane (%), cane yield (kg/ha), sugar yield, and an estimate of relative economic value (REV, $) were determined in each plot. Cane yield was biased by competition effects in the small plots, but this was not the case for sugar content. Genetic correlations between cane yield in one-row plots and the middle two rows of the six-row plots in the same experiment and year averaged 0.49, while the equivalent correlation involving sugar content was 0.91. Measurements of sugar yield and REV were also biased in small plots because of the influence of cane yield. Measurements in small plots were considered in terms of indirect selection criteria for improving REV in large plots (the latter representing REV in pure stands). Selection based on sugar content alone in small plots gave equal or larger gains compared with other selection criteria, including REV itself in small plots. It is suggested that selection in small plots in early stages of selection in sugarcane breeding programs should be based largely on sugar content. Measuring cane yield in such trials may be inefficient and where destructive measurement via mechanical harvesting is involved, may unnecessarily delay progression of selected clones through to the next stages of selection.