Effects of Environmental Conditions and the Coadministration of Growth Retardants on the Response of Sugarcane to Foliar Treatment with Gibberellin1

Abstract

Poor yields of sucrose from sugarcane are often associated with low sucrose:cane ratios, particularly when climatic conditions tend to favor stem elongation rather than sucrose accumulation. Plant growth regulators may be used to modify environmental effects on the growth of sugarcane and thus alter the balance between utilization and storage of sucrose. The objectives of this study were to investigate the influence of temperature, soil moisture, and the coadministration of plant growth retardants on the response of sugarcane to treatment with gibberellic acid. Single foliar applications of GA (gibberellic acid) commercial sugarcane varieties (interspecific hybrids of Saccharum) stimulated stem elongation for from 2 to 6 weeks, but this response was not reflected in higher cane yields unless the plants were harvested within 6 weeks of treatment. A second application of GA at 4 weeks prolonged the growth response. In the field low temperatures were associated with the more prolonged growth responses, which were of smaller amplitude. Moisture stress had no apparent effect on GA response. No correlations were evident between environmental conditions or application rates and the duration of growth responses in greenhouse trials, but the amplitude increased with application rate within the range of 25 to 200 ppm. Three to five immature or semimature internodes were affected. In field trials under warm conditions a period of growth retardation followed the initial GA‐induced growth stimulation. This did not occur in greenhouse trials. Stem‐sugar concentrations fell during the growthstimulation phase, but recovered as growth rates reduced. Attempts were made to accentuate this recovery, and so to increase the accumulation of sugars, by coadministration of growth retardants with GA. Dalapon had a delayed effect on cane growth, slightly curtailing the duration of the GA response, and suppressing growth thereafter. The phase of growth suppression was accompanied by increased stem sugar concentration in greenhouse‐, but not in field‐trials. Sodium silicate (at up to 200 ppm) had no significant effect on growth or sugar accumulation and did not modify the response to GA. Treatment with azauracil (at up to 400 ppm) strongly inhibited cane growth and increased stem‐sugar concentrations, but showed no significant interaction with GA.

Climatic effects on sugarcane ripening under the influence of cultivars and crop age

“…Both variables show a strong inverse relationship with Brix, i.e., the lower the moisture index and the cooler the evenings, more favorable the conditions for ripening. Yates (1972) found that the low air temperatures promoted ripening more effectively than low soil moisture. These results were also reported by Glover (1971), who suggested that in places where there is no water defi ciency, the average air temperature needs to be lower than 21 °C for three months to begin the ripening process.…”

Variation in the sugar yield in response to drying-off of sugarcane before harvest and the occurrence of low air temperatures

“…Thus, there is a positive return between fixed and consumed carbon, resulting in a greater storage. For Yates (1972), the low air temperatures influence more the interruption of sugarcane growth than water stress. Nevertheless, according to Cardozo and Sentelhas (2013), there is no consensus on the thermal parameters of the crop and, in tropical areas, the low air temperatures may not be sufficient to affect the maturation.…”

Hormone content of normal and tall soybeans (Glycine max (L.) Merr.)

“…On the other hand, it has been reported that increasing temperature decreases the responsiveness to application of an exogenous GA and that increasing temperature alone often simulates the effect of GA on intemode elongation (Junttila, 1970;Lester and Carter, 1970;Yates, 1972). These results suggest that at higher temperature, GA metabolism, or sensi tivity to GA, has been decreased compared with that at lower temperature.…”