Abstract

                                Mortimore and Ward (1964) reported that physiological vigour depends upon a steady respiration rate supported by a continuous supply of carbohydrate reserve, always assuming an adequate and balanced level of nutrients. When the vigour of a plant drops below a certain level because of stress conditions under which it is grown, it becomes susceptible to invasion by certain saprophytes and weak parasites. Craig and Hooker (1961) working with Diplodia stalk rot found that a decrease in the sugar level of the stalk causes senescence of pith tissue and susceptibility to pathogens.

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