Botrytis blight of gladiolus: Frequency distribution of infection lesions and their correlation with biochemical constituents

it was observed that the number of infection lesions and severity of the disease were lowest in the topmost leaf and were progressively higher in the subsequent (lower) leaves, up to the fifth leaf from the top. There was a decline in disease in the sixth leaf and the last (normally the seventh) leaf from the top, i.e. the rudimentary leaf, had a still lower frequency of infection. Artificially inoculated plants at pre-and post-spike emergence stage of the crop under laboratory conditions also revealed more or less a similar trend, with the exception that number of infection lesions and the severity of the disease were almost at par in the fifth and sixth leaf from the top. The data showed that the new leaves possess a higher level of resistance against the disease. The fungus on the whole prefered older leaves, except for the rudimentary leaf, indicating its facultative tendency. Since the biochemical constituents, in general, have been shown to have correlation with susceptibility/resistance in a number of hostpathogen combinations, it was considered logical to explore the differences in the biochemical constituents of the different leaves within canopy of gladiolus. The phenols, orthodihydroxy phenols and flavonols were found to be high in the upper two leaves and the lowermost or the rudimentary leaf. Their content was moderate in the 3rd, 4th, 5th and 6th leaf from the top. The total, reducing and non-reducing sugars followed opposite trend to phenols. So far as the minerals, nitrogen and phosphorus are concerned, they followed a trend similar to the total-and reducing-sugars. The potassium levels also followed a similar trend, but in the rudimentary leaves the potassium content did not show decline. It may be inferred that the phenols impart resistance, whereas the sugars susceptibility against infection by the fungus. The nitrogen and phosphorus levels also appeared to be associated with susceptibility to the disease.