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Physiological and Biochemical Approaches in the Selection of Sugarcane Varieties under Different Fertility Levels
Dissertation Abstract:
Five sugarcane varieties, namely, CAC 5711, Co 785, F 156, Phil 56226 and Phil 62120, were grown under field conditions at different fertility levels to determine the in vivo nitrate reductase activity (NRA), total TVD leaf nitrogen content, and specific leaf weight (SLW) from 5 to 8 months after planting. These were studied in relation to sugar yield and its components.
Results showed that NRA increased with increasing fertility levels but decreased with increasing plant age. Activity was highest 6 months after planting or 2 months after the last application of fertilizer N.
Based on endogenous NRA at six months, the ranking order of the five varieties was Co 785 > Phil 56226 > Phil 62120 > F 156 > CAC 5711.
The rate of reduction was found to be influenced by the amount of nutrients received by the plants. With a lag phase of about one hour, maximum activity was recorded at 6, 5 and 3 hours in plants receiving 0, 200 – 100 – 400 and 400 – 200 – 800 fertilizer nutrients (kg/ha), respectively. On the basis of activities at all fertility levels, the varieties ranked as follows: Phil 56226 > Phil 62120 > Co 785 > F 156 > CAC 5711. This ranking appeared to be closely associated with cane tonnage yield of the different varieties.
Ratio values between induced and endogenous NRA decreased with increasing fertility levels, but no correlation was observed between the ratio and tonnage or sugar yield.
SLW increased with increasing fertility levels up to 200 – 100 – 400 kg N-P2O5-K2O per hectare; beyond this level, SLW decreased progressively with increasing fertility levels. SLW also increased with plant age.
Total N content of TVD leaves increased with increasing fertilizer application and decreased with plant age.
A positive correlation was noted between NRA and cane tonnage and sugar yield. However, NRA was negatively correlated with piculs sugar per ton cane (PS/TC).
A significant positive correlation was also observed between NRA and TVD leaf nitrogen, that is, varieties with higher leaf N gave higher NRA values. These relationships could possibly be used as guides in determining the fertilizer requirements of sugarcane varieties.