Effects of flower removal on the development of theSclerotinia/Botrytiscomplex of tobacco

Abstract

Removal of flower heads markedly decreased infection of tobacco by Sclerotinia and Botrytis. Infection was correlated with the density of corollas falling on to the leaves; a greater proportion of those falling from axillary shoots than of those falling from apical shoots incited the diseases. It was not possible to determine whether differences in varietal susceptibility arose from differences in leaf susceptibility or from differences in the ability of the corollas to carry the diseases. Any change in agronomic practice which tended to extend the life of corollas on the plant could lead to increased incidence of these diseases. (i) Agronomic trialsObservations were made on 3 X 3 X 3 factorial trials used to study effects of various cultural practices on tobacco production. Plants, variety 'Hicks', were grown in rows 1.22 m apart and the population varied by spacing the plants 38, 46, or 53 em apart in the rows. Plants were topped at three different heights and at three different stages of growth, i.e., as soon as the flower buds appeared, when the corollas were developing, or when the corollas had started to senesce. The plants were 'clean suckered' by removing all axillary shoots before they had grown 5 em.Three-row plots were planted and disease assessments made on plants in the central row by estimating the proportion of leaf area destroyed approximately 3 weeks after the late-topped plants had flowered.

Germination ofBotrytisandSclerotiniaspores in the presence of pollen on tobacco leaves

“…High proportions of Botrytis and Sclerotinia infections are promoted by plant debris (fallen corollas, pieces of seed capsules, etc.) that have lodged on leaves (Hartill & Campbell 1974). Results (in prep.)…”

“…Senescent corollas lodging on tobacco leaves have been shown to increase the incidence of the BotrytislSclerotinia complex of tobacco (Hartill & Campbell 1974). Only part of the increased disease incidence in plants that had flowered could be attributed to the presence of fallen corollas, and close observation indicated that some other infections originated where clumps of pollen had fallen on the leaves.…”

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

“…General agronomic practices used, and various treatments, based on apical bud and axillary shoot removal (termed "topping" and "suckering" respectively) , have been described previously (Hartill & Campbell 1974). The variety used in the 1969-70 and 1970-71 trials was 'Yellow Gold' and in 1971 both 'Yellow Gold' and 'Hicks' plants were used.…”

“…In this paper "leaf position" refers to the order of emergence, the lowest leaf being the first and the uppermost the last to appear. Plants were inspected twice weekly and assessed for infection as described by Hartill & Campbell (1974) .…”

“…In an earlier paper (Hartill & Campbell 1974) we examined the way in which Sclerotinia and Botrytis infections of tobacco leaves are pro-…”