Cultural and Reproductive Variability of Corynespora cassiicola from Different Host Plants

Abstract

Natural rubber industry plays an important role in the economy of Sri Lanka. Therefore,
improvement of productivity levels has become important. Corynespora leaf fall disease
(CLFD) is the most destructive disease of rubber caused by Corynespora cassiicola. In Sri
Lanka two epidemics occurred in 1986 and 1995. C. cassiicola has a wide host range
including vegetables, ornamentals, weeds, yams, medicinal and other cash crops. Hence,
there is a high risk of cross infection possibilities. The objective of this study was to examine
the diversity of the pathogen isolates from several host plants; rubber-RRISL202 (A), RRISL
110 (B), RRISL201 (C), Eggplant (D), Papaya (E), Tomato (F). Diseased leaf samples were
collected and isolated on potato dextrose agar (PDA). Single spore isolates were obtained and
the cultural variations were studied. Except flat textured D and E, all the other isolates
showed puffy growth. Colony appearance varied from olivaceous green colour to different
shades of grey. Except A, B and C all the other isolates showed concentric rings on lower
surface. Except A and B, the other isolates showed uneven margins. In microscopic view, all
rubber isolates showed thread like hyphae with a width of (3.20-3.58) μm. However, in the
isolates of alternative hosts, hyphae were wider (6.00-7.80 μm). Generally mycelia were
branched and septate with conidiophores at the tips of hyphae. Isolates A, B and C were fast
growers, D and E were moderate while F was slow. In reproductive studies, generally conidia
of C. cassiicola were segmented and showed characteristic hilum at the pointed tips. There
was no significant variation in the dimensions of spores among the isolates. The conidial
length varied from (15-275 μm) and width varied from (3.75-12.50 μm). Straight, curved,
cylindrical and obclavate shapes were observed. Mostly slender, straight conidia were
observed in rubber isolates. Rubber isolates were poor sporulators compared to the alternative
host isolates. Present study revealed that there is a significant variation in the morphology
and reproductive characteristics among the selected C. cassiicola isolates. Further
investigations will be carried out to examine the genetic and pathogenicity variations among
the isolates.

Keywords: Corynespora cassiicola, Alternative hosts, Morphology and reproductive
Characteristics