The influence of genetic variability on the response of the five rice varieties, Cica, Starbonett, Lemont, Bluebonett X IR 43,and IR43,to applied zinc at 0,10,20 and 40 Kg Zn ha-1 under varying cellulose and water management conditions was studied in a greenhouse experiment.
Typical zinc deficiency symptoms, varying in intensity among varieties, were noted, especially in the zero applied zinc treatments. Zinc deficiency symptoms were characterised by blanching at the base of the emerging leaves and rusty brown discolouration in the older leaves.
In all cases the absence of cellulose treatment gave greater plant height, number of tillers/dry matter yield/zinc concentration, and mean uptake of zinc than for the presence of cellulose treatment. Zinc deficiencies were more severe in the flooded treatment compared with intermittent flooding.
Plant height at harvest showed only small and non significant effects of applied zinc except that in the absence of cellulose, Cica decreased significantly in plant height with a 40Kg/ha zinc application. Effects of zinc on the number of tillers were significant in both the plus and minus cellulose treatment .In both cellulose treatment Cica usually had the highest value followed by Bluebonett X IR43, IR 43, Starbonett and Lemont.
Dry matter yield was significantly influenced by zinc application in the plus and minus cellulose treatments. In the plus cellulose treatment at 10Kg/ha of applied zinc, all varieties showed a positive response with IR43 the highest. Between 20 and 40 Kg/ha of zinc application, most varieties showed an increase but Cica and Starbonett decreased. In the minus cellulose treatment all varieties showed an increase with a 40 Kg/ha zinc application with a significant increase for the IR43 and Lemont varieties.
Applied zinc levels significantly affected the zinc concentration of rice shoots and zinc uptake in both plus and minus cellulose treatments. Zinc uptake was much higher in the minus cellulose treatments compared with plus cellulose.
Early maturing varieties such as Cica appeared to be less tolerant of low zinc supply than later maturing varieties such as Bluebonett X IR 43.There was evidence
that high tillering varieties such as Cica,IR43,and Bluebonett x IR43 are able to recover better from early set backs due to deficiency by flooding than low tillering varieties.
The results obtained suggest that management strategies such as choice of variety, treatment of crop residues and water management can be manipulated to affect the incidence of zinc deficiency.