Effects of leaf maturation on development of theSclerotinia/Botrytiscomplex of tobacco

Abstract

In field experiments natural infection of tobacco leaves by Botrytis cinerea Pers. ex Fr. and Sclerotinia sclerotiorum de Bary did not usually occur until approximately 2 weeks after the leaves had completed their main phase of expansion. Exceptions were infections originating from senescing corollas that had lodged on the leaves, but these early infections represented only a small proportion of the total infections that originated from fallen corollas. The age of " leaf at the time of infection was related to its position 011 the plant, a relationship affected by the "topping" and "suckering" treatment applied. When all the flowers were allowed to develop, the upper leaves became infected when they were slightly younger than the middle leaves, but when all the flower buds were removed at an early stage of development, leaf age at the time of infection increased with ascending leaf position. Infection spread faster in the lamina of old leaves than in that of young leaves. Sclerotinia destroyed lamina faster than did Botrytis. The rate of spread of infection within the lamina was not affected by removal of flowering heads.415