Studies on the green and blue mold of Satsuma orange (4)

Decomposition and utilization of pectin by causal fungi

Abstract

This paper gives the result of studies on the pectic enzymes of Penicillium digitatum (green mold) and P. italicum (blue mold) which cause storage rot of Satsuma orange.
Both these fungi excrete pectin-methylesterase (PE) and polygalacturonase (PG) constitutively in asparagine-glucose medium, and adaptively in asparagine-pectin or orange peel extract medium. PG activity is revealed in the infected orange peel tissues.
Optimum pH for PG activity of both fungi lies between 3.6 to 5.5.
Despite the strong pathogenicity, protopectinase activities of P. digitatum and of P. italicum are much lower than those of less pathogenic fungi, P. expansum and P. purpurogenum. This fact suggests that pectic enzymes may be one of the important but not the sole factor of the pathogenicity. A question remains unanswered as to what is the factor which plays another important role in the pathogenicity. Both fungi can, not only decompose the pectin, but also utilize the decomposition product as carbon sources in media containing different nitrogen sources. The decomposition products of pectin by culture filtrates are tri-, di-, and D-galacturonic acid, the former two appearing only in an early stage and the last one in a later stage of decomposition.