Effect of Insecticide, Fungicide, Bactericide, Micronutrient and Growth Regulator on Mango Malformation

摘要

The effect of some widely used agrochemicals on development of mango malformation Fusarium moniliforme var. subglutinans was investigated. The test included insecticides (monocrotophos and dimethoate), fungicide (wettable sulphur), bactericide (streptomycin), micronutrient (borax) and plant growth regulator (naphthyl acetic acid-NAA). The effects of these compounds were tested on the factors that facilitate disease development which included growth of the pathogen, population of the vector (Aceria mangifera) and total carbohydrate content. Factors that inhibit disease manifestation such as growth and population of the antagonist (Aspergillus niger), defense related metabolite (mangiferin) and production of enzymes (peroxidase and polyphenol oxidase) in host were also studied. All the test compounds except sulphur and streptomycin significantly reduced growth of F. moniliforme var. subglutinans in culture; while growth of A. niger was stimulated with sulphur or borax treatment. Other treatments were inhibitory to the growth. In vivo also similar effect of the test compounds on population of A. niger was recorded. The population of A. mangifera in vivo declined by all treatments except NAA. Total carbohydrate of leaves attached to the terminal buds was increased. The insecticides also reduced the amount of mangiferin in treated buds, but in others, it increased. The maximum amount of mangiferin was recorded in NAA treatment. Polyphenol oxidase activity was increased only in treatments with monocrotophos, streptomycin or NAA, and in others, it was lower than the control. However, peroxidase activity was reduced by all the treatments. Similarly, the number of buds colonized by the pathogen was reduced by all the treatments except NAA. But it was significantly lower than the control only with monocrotophos, dimethoate and sulphur treatments. The minimum number of colonized buds was counted in treatment with dimethoate or monocrotophos. But when spraying of monocrotophos was discontinued after a period of prolonged application, mangiferin content and population of A. niger of the treated plants dropped down significantly with concomitant increase in number of infected vegetative buds.