PURSUING HIGHER EFFICACY FOR MANAGED PHOTOPERIODIC INITIATION OF SUGARCANE FLOWERING IN THE TROPICS

THE EFFICACY of managed regimes used in high-cost, photoperiod facilities (PFs) is all important. Various photoperiod regimes were trialled to improve flowering from ≈ 90% treated clones and ≈ 70% treated stalks by reducing the proportion of meristems initiated but not emerged (IBNE). Two experiments in 2007 compared a 60 s/d declination from three commencing day lengths, 12 h 55 min, 13 h 10 min, and 13 h 25 min. Two experiments in 2008 compared declinations of 30, 45, and 60 s/d for the panicle development phase following an initiation declination of 60 s/d. In 2009, three experiments compared initiation and developmental declinations of 60 and 40 s/d, and an initiation and developmental declination of 60 and 20 s/d, respectively, with a drop of 30 min in day length after 28 day’s initiation. There were no differences among treatments in 2007. For clones, 87.9 and 84.4% flowered, while 62.3 and 56.7% of treated stalks produced usable panicles. However, 20.0 and 19.4% of stalks were IBNE. In PF(A) in 2008, flowering from 30 (70.6% treated stalks) vs 60 s/d (65.9%) and 30 vs 45 s/d (77.1%) developmental declinations were not significantly different but was for the 45 vs 60 s/d declinations. Meristems IBNE averaged 23.8%. On average 90.1% of clones flowered. In PF(B), the control (60 s/d) produced an anomalous result. The 45 and 30 s/d declinations did not differ, with 85.5 and 78.1% of treated stalks and 92.5% of clones flowering. In 2009, the 60/20 s/d declinations, separated by a 30 min day length decrease disappointed, with 52.8% stalks and 74.4% clones flowered. The 60/60 s/d (control) and 40/40 declinations did not differ significantly, producing 78.5% flowered stalks from 93.5% flowered clones, on average. Results for the 40 s/d regime, 81.6% flowered stalks and 14.7% IBNE, are the best results yet achieved. Significant differences were obtained among regimes for pollen fertility, but pollen fertility was not a limitation for cross pollination. Comparison of in-field vs managed PF flowering showed the superiority of the latter at 188 and 669%, in 2008 and 2009, respectively. Mean fuzz weight of PF crosses was lower than that of core crosses, but mean seed germination of non-germination tested PF crosses was equal to or better than germinated-tested core crosses.