Influence of Sub- and Supra-Optimal Concentrations of Some Growth Regulators On Growth of Guava, Phenol Status, Nitrogen Concentration and Numbers of Meloidogyne Incognita

Abstract

The effects of several plant growth substances on the growth of guava, root-knot development, phenolic content and nitrogen concentration were studied using sub- and supra-optimal doses applied as foliar sprays. Shoot and root growth were stimulated by sub-optimal doses of growth retardants and promotors but retarded by supra-optimal ones. Sub-optimal doses of CCC and daminozide plant retardants stimulated stem elongation and internode length and increased the numbers of nodes, branches and leaves. Supra-optimal doses of ethephon and GA plant stimulators had the reverse effects. The multiplication of Meloidogyne incognita at sub- or supra-optimal rates of growth retarding or stimulating substances was greater in treated than in untreated plants, but the degree of root-galling was sometimes independent of population density. Effectiveness of plant growth regulators on host growth and associated nematodes seems largely dosage dependent. There was an accumulation of phenols in treated tissues compared with those translocated or synthesized in untreated roots. Some 26.5 times more accumulated phenols were observed after a CCC subdose than in untreated controls. The mono/poly phenol ratio seemed to influence root galling. Nitrogen concentration varied little.