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THE CHOCOLATE SPOT DISEASE OF BEANS ( VICIA FABA L.) CAUSED BY BOTRYTIS CINEREA PERS
Author(s) -
WILSON A. R.
Publication year - 1937
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.1744-7348.1937.tb05033.x
Subject(s) - botrytis cinerea , biology , botrytis , spore , vicia faba , aphis , mycelium , botany , horticulture , hypha , spots , aphid
SUMMARY Chocolate spot disease of broad and field beans in Britain is caused by forms of Botrytis cinerea. This disease should not be confused with the chocolate‐coloured lesions of Aphis injury, frost injury, mechanical injury, etc., and leaf spot ( Cercospora Fabae and Ascochyta Fabae). All forms of Botrytis cinerea tested and some other species of Botrytis were capable of causing chocolate spot. B. cinerea will attack other species and genera of the Leguminosae, producing in some instances lesions similar to those of chocolate spot disease of beans. Chocolate spot infection is of two types, “aggressive”, causing blackening and death of part or the whole of the shoot system, and “non‐aggressive”, causing discrete or coalesced chocolate‐coloured lesions. The former type of attack is responsible for the greater part of the damage done by epidemics of the disease. Under suitable environmental conditions, there is a progressive increase in the total number of visible lesions over a period of at least 5 days after treatment with a suspension of Botrytis spores. When a dilute spore suspension is used “non‐aggressive” infection occurs. When a dense suspension is used, “progressive” infection results in “aggressive” infection: if, however, plants are removed after 24 hours to an environment unsuited to infection, the attack remains “non‐aggressive” While hyphae are abundant in the lesions of “aggressive” infection only a sparse mycelium is present in those of “non‐aggressive” infection. The maximum temperature for infection is about 30° C, the optimum about 20° C. and the minimum between +1 and ‐1° C. A water film is essential for infection, and any factors increasing the rate of evaporation of this film inhibit or decrease infection. The optimum conditions for “aggressive” infection are ( a ) the presence of large numbers of spores of the pathogen, ( b ) rain, ( c ) high humidity and rain to maintain the water film on the foliage for some days, ( d ) little or no wind and ( e ) a temperature between 15 and 20° C. Statistical treatment of data has established a correlation between rainfall and the severity of chocolate spot disease. Epidemics are correlated with abnormally heavy rainfall during the critical months of April, May, June and July. Spores of B. cinerea will remain viable on the leaf surface for periods of more than a month under adverse conditions. Any factor tending to weaken the crop, such as sour soil, potash and phosphate deficiency and waterlogging of the soil, renders it more liable to “aggressive” infection. In addition, chocolate spot disease appears to be favoured by a dense stand of beans and shelter from the prevailing wind. No economic method of control has been found. Care should, however, be taken to see that the crop is not weakened or in any way rendered more liable to attack.