Anurag Sunpapao and Chaninun Pornsuriya

pp. 507 - 512

Abstract

Leaf fall is a serious disease of para rubber seedlings, known to cause economic losses in several nurseries of southern
Thailand. It is caused by a phytopathogenic fungal-like organism Phytophthora. Chitosan is a biological polymer used as
a plant growth stimulator, and used against several phytopathogenic fungi on many crops. This study aimed to determine the
effects of chitosan in controlling leaf fall disease of para rubber seedlings caused by Phytophthora palmivora, both in vitro
and in vivo. Various concentrations of chitosan were applied on seedlings of para rubber clone RRIM 600. The growth rate of
P. palmivora on potato dextrose agar was determined with various chitosan concentrations, and a concentration of 1 mg/ml
was sufficient to reduce the radial growth of P. palmivora by about 91% on agar plates. This concentration also reduced the
size of necrotic lesions at 24 and 48 hours post inoculation (hpi), but not after 72 hpi. The results suggest that chitosan (i)
directly inhibits the growth of P. palmivora, and (ii) reduces the growth rate of necrotic lesions, but may not completely be
able to control the leaf fall disease of para rubber seedling.