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.
