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THE ADAPTATION OF FUNGI TO FUNGICIDES: ADAPTATION TO CAPTAN
Author(s) -
PARRY K. E.,
WOOD R. K. S.
Publication year - 1959
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1959.tb02518.x
Subject(s) - captan , agar , spore , fungicide , biology , germination , venturia inaequalis , spore germination , food science , botrytis cinerea , sucrose , horticulture , botany , microbiology and biotechnology , bacteria , genetics
In sucrose‐nitrate liquid media Botrytis cinerea was able to grow from spores when the media contained captan at concentrations up to three‐quarters of the saturation value. Because of this, and the low water solubility of the fungicide (< 1 p.p.m.) all attempts to produce resistant strains were made with agar media. Spores did not germinate when applied as a suspension in water to the surface of a sucrose‐nitrate agar containing 500 p.p.m. captan; about 1% germinated when the concentration was 250 p.p.m. Similar results were obtained when an agar extracted with water and pyridine was used. There was some growth from spores on agar containing 250 p.p.m. captan; this always started at the edge of the agar. Resistant strains were produced when disks were transferred from cultures growing on agar containing low concentrations of captan to agar containing higher concentrations. By repeating this process over a period of months a strain was produced eventually which grew slowly but continuously, and sporulated on agar containing 250,000 p.p.m. captan. However, the very low solubility of the fungicide made it difficult to assess quantitatively the degree of adaptation. Although agar disk inocula from resistant strains retained their resistance on transfer to captan agar, inocula consisting of suspensions of spores only, or of hyphae and spores, were no more resistant than the parent strain. The resistant strain retained the first type of resistance after it had been grown on fungicide‐free media for four periods of 2 weeks. Spores from the resistant strain were more resistant than spores from the parent strain in germination tests with drops on glass slides; a concentration of 0·6 p.p.m. captan prevented germination of parent spores, but one or two spores out of a total of some 4000 spores of the resistant strain germinated at concentrations of 100 p.p.m. This type of resistance, transmissible by spores, was reduced when the resistant strain was grown on fungicide‐free agar. Spores from resistant strains had a very low viability, although they were produced normally and were normal in size and appearance; when obtained directly from a culture on a captan medium only 2% germinated whereas in similar conditions there was 100% germination of parent spores. Viability was increased to 13% after one transfer on a fungicide‐free medium but was no more than 52% after four transfers. Preliminary attempts to obtain strains of Venturia inaequalis resistant to captan were unsuccessful. The significance of the results obtained is discussed.