Pigment Production From Tyrosine by Australian Isolates of Phytophthora Species

Abstract

Pigment production from tyrosine by 138 isolates of 12 Australasian species of Phytophthora was followed photodensitometrically. Optimal production occurred on a casein hydrolysate-tyrosine medium at pH 6.0, when sugars were absent. The mean pigment production of northern ecotype isolates of Phytophthora drechsleri ( = P. cryptogea) was significantly greater than that of southern ecotype isolates, and the mean pigment production of A1 compatibility type isolates of P. parasitica was approximately double that of A2 type isolates. Little or no pigment was produced by any of the isolates of P. cinnamomi examined. While pigment production, per se, appears to be a poor taxonomic criterion, it is suggested that the degree of pigment production by unknown isolates might in some cases prove helpful as a confirmatory characteristic following species identification by morphological criteria, and as a preliminary screening technique particularly applicable to the recognition of P. cinnamomi among Phytophthora isolates obtained from native vegetation in Australia.