Metabolic responses of tomato plants to metribuzin herbicide by in vivo and in vitro techniques

ABSTRACT

The effect of metribuzin at different doses [0.25, 0.5, 0.75 and 1.0kg ha-1] was studied on intact pot normally-grown seedlings of two tomato genotypes [Lycopersicon esculentum Mill, cv. Karnak vfnt F-1 and Castle rock]. The herbicide caused significant inhibitions in dry weight and protein contents of shoots and roots of both tomato genotypes. Significant reductions in chlorophyll, carotenoids, glucose, sucrose and starch were observed. The reduction was more pronounced at higher metribuzin doses. Possible tolerance to the herbicide in both genotypes was checked using tissue culture methods. Cotyledons and leaf discs from shoots regenerated on media containing different concentrations of metribuzin [0, 0.63, 1.25, 2.5, 5 and 10 mgM]were used to initiate three successive cycles of selection. Similar to potted plants, significant reductions in dry weight and protein content in shoots and roots of the in vitro selected plants were observed as well as in contents of chlorophylls, carotenoids, glucose, sucrose and starch of both tomato genotypes. The inhibition was remarkable at the high concentrations of metribuzin throughout the three cycles of selection. The magnitude of inhibition was relatively lesser in the 3rd cycle compared to the 1st or the 2nd cycles. Therefore, the effects of metribuzin on tomato appeared as declined after three cycles of the in vitro selection. Such decline could be regarded as a partial recovery response. This recovery response after three cycles of in vitro selection could point to a possibility of some developed resistance to the herbicide throughout the successive cycles