Metabolism of Colletotrichum lindemuthianum (Sacc. & Magn.) Scribner and infected Vigna sesquipedalis Fruw

by Wong, Yee-on

(Uncorrected OCR) Abstract of thesis entitled

"METABOLISM OF COLLETOTRICHUM LINDEMUTHIANUM (SACC. & MAGN.) SCRIBNER AND INFECTED VIGNA SESQUIPEDALIS FRUW~

submitted by

PAULINE WONG YEE ON ( ~~~ ) B. Sc. (General, H.K.)

for the DEGREE OF MASTER OF PHILOSOPHY at the UNIVERSITY OF HONG KONG

in 1974

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ABSTRACT

Colletotrichum lindemuthianum is a presumptive

necrotrophic parasite. When the second trifoliate leaf

of the bean plant Vi~a sesquipedalis was infected with

conidia of ? lindemuthianum, a sequence of external

symptoms could be observed, beginning 24 hours after

inoculation and continuing to 120 hours after inoculation

when the infected portion became senescent. The fungus

predominately attacked veins of the leaf but both veinal

lesions and mesophyllous lesions were observed at 24

o

hours after inoculation (temperature = 26 C); the lesions

developed further thereafter. Sporulation started at

48 hours after inoculation and was most intense at 72

hours after inooulation. Chlorosis set in at 48 hours

after inoculation whereas necrosis set in at 72 hours

after inoculation. Both"symptoms increased gra.dually

until 120 hours after inoculation when the infected

portion was obviously badly damaged andbec~e senescent.

The main effect of infection was to reduce the dry

weight of the infected leaf and, to a small extent, the

stem of the infected plant. There was a gradual,

proportional reduction in both chlorophyll content and

rate of photosynthesis starting from 24 hours after

inoculation and continuing throughout the cou[se of

disease development. On the contrary, the rate of respiration

increased slightly from 24 hours after inoculation and

the maximum rate of respiration was at 72 hours after

inoculation. From then onwards, the rate gradually

decreased and at 120 hours after inoculation, the rate

of respiration fell below that of the control. Indications 14

of local accumulation of C-compound were observed only

at 24 and 48 hours after inoculation; moreover, the

pattern of translocation was not changed as a result of

infection.

The fungus was found to grow best on LB+glucose

medium and was metabolically most active at 4 days after

o

incubation at 26 C. The pattern of carbohydrate conversion

by the fungus in the in ~ experiments was comparable

to that in the!!!i!2 experiments. In the ~~

experiments, the fungus utilized the predominant host

carbohydrate, sucrose, starting from 24 hours after

inoculation and converted it gradually to characteristic

fungal carbohydrates such as trehalose, mannitol, arabitol

and erythritol. However, this pattern of conversion was

stopped in the in !i!2 experiments at 120 hours after

inoculation.

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