CHEMICAL ECOLOGY AND MANAGEMENT OF Phytolyma fusca WALKER (HEMIPTERA: PSYLLIDAE) USING ORGANIC AMENDMENTS ON Milicia excelsa C.C. BERG

Abstract

Milicia excelsa (Me) is an important timber tree whose establishment has been constrained by Phytolyma fusca (Pf) attack. A commonly used method of Pf control with systemic pesticides has been unsuccessful but cultural management with organic amendment could be feasible. Information on the chemical interactions between Pf and Me, and effectiveness of organic amendments for the management of Pf is scanty. Therefore, phytochemical constituents, reactive oxygen species of Me seedlings attacked by Pf and effect of soil amendments on its growth and gall formation were investigated. Seeds of Me (n=272) collected from a mother tree were germinated and raised in a screen cage, out of which 20-seedlings were collected and infested with Pf following standard procedure. Galled Leaves (GL) and Healthy Leaves (HL) were analysed at 32- and 64-weeks for phytochemical contents using Gas Chromatography-Mass Spectrometry. Third-leaf from the apex of healthy seedlings (n=12), aged 32-weeks were mechanically wounded using a sterile needle perforator, excised after 6 hours; and analysed using standard staining technique for Superoxide Anion (SA) and Hydrogen Peroxide (HP). Soil was amended with Poultry droppings (Pd), Cattle dung (Cd) and Pig faeces (Pgf) at ratio 2:1. Sixty replicates of healthy seedlings (n=240), aged 24-weeks were randomly transplanted and immediately exposed to Pf, while seedlings on untreated soil served as control. Seedling survival (SS),%, Seedling height (SH),cm, Collar diameter (CoD),cm and Number of galls (NoG) were assessed fortnightly for 22 weeks. Data were analysed using descriptive statistics and ANOVA at α0.05. Six phytochemicals; tannins, flavonoids, alkaloids, saponins, steroids and terpenoids were identified in GL and HL at 32- and 64-weeks, respectively. Alkaloids were higher in GL (2.44±0.02%) and lower in HL (2.12±0.03%) at week-32. Saponins, terpenoids, tannins and flavonoids decreased from 0.09±2.08 mg/g, 0.55±0.01 mg/g, 0.44±0.45 mg/g, 0.49±0.08 mg/g in HL to 0.01±0.01 mg/g, 0.16±0.07 mg/g, 0.23±0.06 mg/g, 0.23±0.06 mg/g in GL at week-32, respectively. At week-64, saponins and alkaloids were higher in GL (0.25±0.16 mg/g and 6.30±0.14%) and lower in HL (0.17±2.08 mg/g and 3.78±0.13%), respectively. Terpenoids, tannins and flavonoids were higher in HL (0.70±0.31 mg/g 0.84±0.85 mg/g and 0.73±0.39 mg/g) and lower in GL (0.54±0.43 mg/g, 0.57±0.65 mg/g and 0.50±0.19 mg/g), respectively. Numbers of Heterocyclic Compounds (NHC) in the GL (18) was lower in HL (20) at week-32. Also, NHC in GL (15) reduced by 45% and HL (18) by 47% at week-64, respectively. Terpenoids present in HL were absent in GL at week-64. Brown colouration on wounded leaf- tissues indicated the presence of HP while SA was absent in both leaf treatments. The SS was least in Pd (50.0%) and highest in control (80.0%). The SH and CoD significantly increased from 23.4±0.82 to 46.21±2.59; and 0.46±0.02 to 0.77±0.03, in control and PD seedlings, respectively. The NoG was lowest in CD (0.75±0.06) and highest in control (1.25±0.09). Heterocyclic compounds in galled leaves reduced with persistent attack, while Phytolyma fusca activity decreased the amount of terpenoids in healthy leaves. Mechanical wounding induced hydrogen peroxide production. Soil amendment with poultry droppings enhanced growth of Milicia excelsa seedlings.