Resistance Mechanisms of Solanum spp. Resistance Mechanisms of Solamun spp. Biotypes Depending on Metribuzin

Abstract

Metribuzin is a herbicide belonging to the triazinone chemical family. It is applied pre-emergence and post-emergence in weed control in potato planting areas. Metribuzin shows its mechanism of action by binding to the D1 protein in photosystem II, stopping the electron transfer required for photosynthesis, and by causing oxidative stress in target plants, leading to death. However, some weed species can develop different resistance mechanisms due to long-term herbicide use. However, Solanum spp. (Dogberry), which is from the same family as potato, is increasingly ineffective in most cases in the control of weeds and causes significant crop losses in Türkiye. In this study; The reasons for the resistance of Dogberry populations in Niğde potato planting areas to metribuzin were investigated. The reasons for metribuzin tolerance of resistant nightshade populations collected from potato plantations, metribuzin uptake into the plant body via roots and leaves, transport to the target area, and metabolism (detoxification) of plants in different organs were investigated.

In the first stage, 4 populations suspected of resistance from potato plantations and 1 susceptible population from outside potato plantations that were not exposed to metribuzin in any way for comparison purposes were examined in simplified systems with temperature and humidity control under laboratory conditions.

Metribuzin tolerance of different biotypes was evaluated by determining metribuzin adsorption capacities, transfer rates of the molecule to the above-ground parts of plants, metribuzin concentrations and metabolites in leaves and other plant parts, which are the target area of ​​metribuzin. Metabolism rates in different organs and metabolites that emerged were determined in more detail. This study utilized various radiometric methods (different extraction methods, Radio-HPLC (radiochromatography), autoradiography, oxidizer, etc.) using 14C-metribuzin (radioactive metribuzin labeled with 14C).

Biotypes with suspected resistance obtained from potato plantations where metribuzin has been applied continuously for many years show more tolerance to metribuzin than biotypes obtained from uncultivated soils. The metribuzin uptake capacity of Solanum nigrum species from the roots is high and its transfer to target organs is high. This behavior is due to the strong hydrophilicity of this molecule (Kow = 1.6). However, autoradiographic studies show that metribuzin residues in the plant are compartmentalized and radioactivity is retained in conductive tissues. The values ​​obtained for metribuzin concentration at the target tissue level are very different depending on the biotypes studied, with significant differences in the critical concentration at the leaf level.

It was determined that metribuzin taken from the roots was rapidly metabolized within a few days. Therefore, the concentration of metribuzin in the stem and leaves is quite low. There are differences in the metabolites resulting from the metabolism of metribuzin in the roots and above-ground tissues of the plants. It was determined that many lipophilic metabolites were formed in the roots along with various hydrophilic conjugated residues; only conjugated residues were found in the leaves.

As a result; the tolerance of the biotypes found in potato plantations may be related to the low capacity of metribuzin to be transported to the chloroplasts, which are the main target area. This situation can be attributed to the very active detoxification capacity of the herbicide at the root level on the one hand and to its equally remarkable potential for root and stem decomposition (retention in vascular tissues); thus, the transfer of the active substance to these chloroplasts can be greatly reduced.
When all these results are evaluated, post-emergence applications of metribuzin can facilitate the access of metribuzin to the leaves (chloroplasts), which are the main target area, and the absorption of the entire application dose into the plant body only through leaf penetration. Thus, it can be more effective by bypassing the retention and metabolization stages by the roots and vascular bundles.