TROPICAL, MANAGED INITIATION OF SUGARCANE FLOWERING: OPTIMISATION OF NON-PHOTOPERIODIC VARIABLES

POOR flowering in tropical sugarcane programs poses a considerable impediment to genetic improvement of the crop. Major limitations are imposed by environmental variables. Some of these can be alleviated only by use of managed photoperiod facilities. Research conducted in such facilities, and reported in this paper, aimed to further our management of the initiation process in sugarcane and so optimise use of these facilities. Ten experiments were conducted in the photoperiod facilities located at BSES Meringa from 1998 to 2003. Variables studied included potting media, pot size, plant density, pot location, and nutrition. Research resulted in a change from use of a three-component potting medium to coarse river sand. Use of 33 L pots produced the best results. Placement of these contiguously on the trolleys does not disadvantage flowering. Pot position on the trolley does not affect flowering. Three plants per pot, maintained as single stalks, is preferable to free tillering of a single propagule. Use of a complete, dissolvable fertiliser continuously throughout plant growth and panicle initiation and development phases has been adopted over a broken regime. The importance of nitrogen in the initiation process has been highlighted, an increased nitrogen level resulting in reduced, delayed flowering. Better definition of the lower and upper acceptable bounds for nitrogen nutrition for flowering is required. Methods for precise delivery in a practical context require further research. This series of experiments developed an optimised system that uses plants in a stress-free environment to produce > 73% flowered stalks and > 88% flowered clones. This is in marked contrast to flowering under natural conditions. Accession to the remaining germplasm will require use of non-flowering clones, from previous experiments, in studies to further optimise the initiation system. This most likely will result from additional finetuning of the photoperiodic regime.