EFFECTS OF NARROWING GENETIC BASE AND ABIOTIC STRESS ON LEAF SPOTTING IN GREVILLEA ROBUSTA

Abstract

Kimatu JN. 2011. effects of narrowing genetic base and abiotic stress on leaf spotting in Grevillea robusta.
Grevillea robusta is a widely grown agroforestry tree and is regarded as a pioneering coloniser of disturbed
sites. Our current understanding on changes of species due to disturbance, abiotic conditions and biotic
interactions is very minimal. We investigated a leaf-spotting disease and abnormal growths on G. robusta in
Yala and Kodera forest plots in Nyanza province, Kenya. The study comprised symptomology, identification
of causal pathogens as well as tissue and soil analyses. Phyllosticta spp. and Pestalotia spp. fungi were isolated
from the leaf spots. Seedling reinoculation confirmed Phyllosticta spp. as the lesser opportunistic cause of
the leaf spot. However, mineral and proteoid root analyses suggested that abiotic and genetic factors were
the main causes of the leaf spotting. The Yala forest had lower pH, phosphorus toxicity (> 0.07%) and poor
water drainage, while the Kodera forest had generally high manganese toxicities in soil and leaf tissue.