The Taxonomy of the Brown Rot Fungi (Monilinia spp.) Related to their Extracellular Cell Wall-degrading Enzymes

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Abstract
Patterns of extracellular enzymes secreted by the brown rot fungi M. fructigena, M. fructicola, M. laxa and M. laxa f. sp. mali were studied by column isoelectric focusing. Of the 4 enzymes assayed, .alpha.-L-arabinofuranosidase (AF) showed the greatest differences between species. Thus M. fructicola had high AF activity at isoelectric point (pI) 5.1, M. fructigena had AF peaks at pI 3.0 and 7.0, M. laxa showed activity over the pI range 6.0 to about 7.3 with distinct peaks at 6.7 and 7.2 and M. laxa f. sp. mali had very high AF activity at pI 7.2. The pectinlyase (PL) patterns were also useful for identification: the characteristic molecular form of PL in cultures of M. laxa and M. laxa f. sp. mali was at pI 9.1; the 2 other species showed single peaks of activity at about pI 8.5. Some M. laxa isolates also produced a peak at pI 8.5, although this was less active than the characteristic one at pI 9.1. The polygalacturonase and pectinesterase enzyme patterns were not useful for distinguishing between the Monilinia fungi. The AF and PL enzyme patterns from known isolates were used to identify several unknown brown rot cultures, including M. laxa isolates from stone fruits in Australia and M. laxa from Stranvaesia undulata, a new host in England.