Flowering and lodging, physiological-based traits affecting cane and sugar yield: What do we know of their control mechanisms and how do we manage them?

Abstract

Understanding flowering and lodging, or loss of crop erectness, in sugarcane is crucial for development of selection strategies to reduce their impact in commercial production systems and for flowering in breeding programs. Experiments conducted on Australia's tropical northeast coast, established the economic importance of flowering and lodging and provided insights into their control mechanisms. The effect of flowering on yield was determined using lit and unlit night regimes. Photoperiods at low and intermediate tropical latitudes (2° versus 17°) were contrasted for their effect on flowering. Losses for cane yield, sugar content, and sugar yield from flowering were 6.8, 3.0, and 9.4%, respectively. The latter equated to the penalty used in BSES Limited's tropical program for free, early season flowering. Sub-optimal photoperiod is largely responsible for poor and variable flowering in programs located close to the equator, and this may be confounded with high day temperature. The effect of six moisture regimes on panicle initiation and development was studied. Moisture regimes did not differ for flowering within crops, but differences between crops (29.4% versus 0.8% flowered stalks) coincided with an El Niño event and high temperatures in the ratoon crop, proving adequate soil moisture is not a sufficient condition for flowering. Seven early season phenotypic plant descriptors and two structural stalk traits were assessed as predictors of harvest erectness. Brix, commercial cane sugar (CCS), and fibre of erect and lodged stalks were determined to assess the impact of lodging prior to and within the harvest season. The interactions of the effects of cultivars with planting depth and mounding on erectness were examined. All phenotypic traits, except stalk height, and two structural stalk traits correlated poorly with plant erectness at harvest. Regression analyses revealed leaf width, plant top length, and stalk number were significant predictors of crop erectness at harvest, but their practical relevance is unclear. Pre-season loss of erectness and stalk condition (sound or unsound), resulted in a 12 and 8% loss of CCS, respectively, and a 24% loss combined. Erect- and lodged-stalk CCS increased during the season. The marked differential between classes in July (18 and 23% of erect stalks, in two crops) decreased by September (10 and 11%). The effect of increasing depth of anchorage approached significance suggesting crop erectness can be enhanced using appropriate cultural practices. Selection against flowering has been very successful and is justifiable economically. Poor flowering constrains achievable genetic recombination, but managed photoperiod regimes, combined with management of key environmental variables, alleviates this. Loss of CCS due to lodging is economically critical. Crop erectness via ideotype selection is achievable, but development of early season, aboveground traits as predictive variables has proven elusive.