Some properties of SENCOR (Metribuzin) and bases for variation of its effect on Solanum nigrum and Solanum sarachoides : a thesis presented in partial fulfilment of the requirements for the degree of Master of Horticultural Science in Plant Science

Abstract

In Part I of this study, the relative potencies of SENCOR and its metabolites have been investigated. SENCOR has been established as a potent Hill reaction inhibitor. The observed action of SENCOR and its metabolites are discussed in terms of structure/activity relationship The mechanism of action of SENCOR and one of its metabolites is compared with other known Hill reaction inhibitors. A scheme is then proposed for the mode of action of Hill reaction inhibitors. In Part II the observed variation in the field, in the response of Solanum nigrum and Solanum sarachoides to SENCOR has been established as a phenomena of species selectivity From studies on uptake, distribution and metabolism of radio active SENCOR it has been established that a restriction to movement of the herbicide from the xylem to the mesophyll occurs in Solanum sarachoides (tolerant species) while the material is distributed throughout the mesophyll in the susceptible Solanum nigrum. This restriction to movement into the mesophyll in the tolerant species has been confirmed by studies on the inhibition of rate of transpiration and from effects on stomata. SENCOR also appears to be metabolised to a greater extent in the tolerant species This study leads to the conclusion that the protection of the active centre, the chloroplasts, through restriction to movement of SENCOR into the mesophyll, combined with partial breakdown of the herbicide in the plant may be responsible for the tolerance of Solanum sarachoides to SENCOR.