Studies on host-parasite relationshiops of colletotrichum gloeosporioides on rubber ( Hevea brasiliensis)

Abstract

C o n l d l a o f C o l l e t o r l c h u B gloooaporioid&s on agar coated s l i d es K«ruinated w i t h i n a short p e r i o d of 3 h . Clusters of secondary c o n l d l a were produced i n abundance at 2k h, but no a p p r e s s o r i a were detected at t h i s stage* Although, at 3 h, l e a e h s t e of clone RRIC 100 s i g n i f i c a n t l y depressed conidial germination, they germinated e q u a l l y well i n l e a c h a t e s of a l l clones •t 9 h. Maximum and minimum colony growth was reoorded i n l e a c h a t e of clones PB 86 and RRIC 100, r e s p e c t i v e l y . Growth of the fungus i n l e a c h a t e of clone RRIC 52 and 103 was l e a s than that of PB 86 but was more than i n RRIC 52. There IU a r a p i d i n c r e a s e i n growth from 6 to 9 b i n both RRIC 52 and 103, but the Increase i n growth i n RRIC 100 and PB 86 was g r a d u a l . Germinating c o n l d l a in leachate of clone PB 86 produced s i g n i f i c a n t l y more germ tubes than other clones, at 2k h a f t e r i n c u b a t i o n. The a p p r e s s o r i a were formed around 9 h a f t e r i n o c u l a t i o n i n leachates of a l l c l o n e s , except PB 86. However, by 2h h q u i t e a high percentage of c o n i d ia formed a p p r e s s o r i a , highest being recorded i n leaehste of clone RRIC 52. A s o l u t i o n of Sucrose favoured more fungal growth than Glucose, Fructose and Maltose. Germination o f c o n i d i a was delayed i n a s o l u t i o n of Maltose. Leaves of clone PB 86 supported the maximum growth of the fungus while the l e a s t growth was recorded on clone RRIC 52* However, the progeny of these teo clones i . e . RRIC 100 and 103, showed an i n t e r m e d i a t e type of growth. : The a p p r e s s o r i a were f l r a t observed on l e a v e s about 6 h a f t er inoculation. They were dark brown and r e l a t i v e l y l a r g e compared to the conidium. The most number o f a p p r e s s o r i a were seen i n clone RRIC 52 while r e l a t i v e l y a few were observed i n clone RRIC 100. P e n e t r a t i o n and p o s t - p e n e t r a t i o n s t u d i e s r e v e a l e d that the c o n i d ia germinated r e a d i l y on the l e a f surface with a p p r e s s o r i a being found along the junctions of the epidermal c e l l s . The i n f e c t i o n hypha, formed at the point where the appreeaoriuB contacts the host t i s s u e , penetrates d i r e c t l y i n to the aesophyll t i s s u e s through tho epidermis *to h a f t e r i n o c u l a t i o n . Well devclopod a c e r v u l i were foraed by r u p t u r i n g the upper and lower e p i d e r a al c e l l s at 72 It a f t e r i n o c u l a t i o n . At t h i s stage, aoae d i s o r g a n i s a t i o n of •esophyll c e l l s was a l s o evident.