INFLUENCE OF PLANT METABOLITES ON FLEA BEETLE, Phyllotreta mashonana (Coleoptera, Chrysomelidae) DAMAGE ON SPIDER PLANT, Cleome gynandra. L. MORPHOTYPES

Abstract

Spider plant (Cleome gynandra.L) is an African Leafy Vegetable (ALV). The crop is well adapted to a wide range of ecologies and has been differentiated into three main morphotypes based on the stem colours of purple, purple-green and green stemmed morphotypes. The plant plays an important role as a source of nutrients, income and traditional medicines in Kenya. However, production of spider plant in Kenya has been constrained by poor agronomic practices, plant genotypes which are less productive and pests. Flea beetle (Phyllotreta mashonana) is an important pest which accounts for 25 % foliage damage in the plant manifested as “shot holes.‟‟ The reported damage however, was variable among the morphotypes. The study aimed at determining the level of damage inflicted on the three main spider plant morphotypes in relation to the nutritive value and phytochemicals of importance for plant defense and/or pest attraction. The research entailed propagation of three spider plant morphotypes inside a screen house in a C.R.D. Flea beetles were introduced after seven weeks of growth to determine the damage caused by the beetles on the leaves which was assessed using the Bailey scoring scale of 0-3, 4-7 and>7 holes per leaf. The data on damage inflicted by the flea beetle was log transformed to standardize the variance and then analysed using ANOVA. The means were separated using L.S.D 0.05. It was observed that, the purple stemmed morphotype was the most damaged with 8.6 holes p<0.05, while the green stemmed morphotype was least damaged with 2.7 holes p<0.05. Quantitative determination of nutrients and secondary metabolites was done on the foliage taken on the 7th week of growth. Proximate test was done to determine the carbohydrates and proteins were determined by Kjedahl method. Determination of the secondary metabolites and vitamins was done using the High Power Liquid Chromatography (HPLC). There was a significant difference p<0.05 of the primary and secondary metabolites among the three morphotypes with purple stemmed having the highest quantities of carbohydrates, proteins, vitamins and glucosinolates. The purple morphotype had the least terpenoid quantities. In contrast, the green morphotype had the least primary metabolites and glucosinolates with the highest quantities of terpenoids. Correlation analysis showed a positive relationship of primary metabolites and glucosinolates with the flea beetle damage, while a negative correlation was noted between the terpenoids and the flea beetle damage r=-0.794. From this study, it was concluded that, the purple stemmed morphotype was the most susceptible to the flea beetle damage and green stemmed was the least susceptible. In addition, it emerged that the inflicted damage in spider plant morphotypes by the flea beetle is largely metabolomically influenced and that primary metabolites and glucosinolate levels are antagonistic to the terpenoids levels in the morphotypes, so do their flea beetle resistance roles. It can therefore be recommended that, plant breeders can use the green stemmed morphotype to improve the resistance of the more nutritious but flea beetle susceptible purple stemmed morphotype in order to increase the yields and maintain the nutritional potential of the morphotypes.