Information in the literature suggests that the process of apple bud morphogenesis is controlled by the level of growth substances, notably gibberellins in the bud, and by the availability of growth substrate ( S ). The spur buds of apples must contain a certain minimum number of nodes ( Nm ) before flower primordia can be formed, and the process of bud morphogenesis can be described by a rate of node production with time, t by the equation dNdt=YakGkrS1+cS It is postulated that the parameter kG is a function of the balance between the enzymes systems in the bud, the rate of synthesis of the enzymes associated with the development of floral bud parts (floral enzymes) being inversely related to the level of gibberellins ( G ) in the bud. The parameter kG is a function of the nutritional state of the bud; a is a rate parameter, and i is a conversion factor. Node production rate is asymptotic with increase in S , but switches from high to low values as G varies about a critical concentration. The implications of the model, which appears to describe most observations, are discussed, and some suggestions for testing it are put forward.
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Landsberg et al. (1975) studied this question.