The effects of pyridate on 15 different chickpea (Cicer arietinum L.) genotypes have been investigated under controlled environmental conditions. Different degrees of tolerance to pyridate were detected. Pyridate applied at 2.0 and 4.0 kg active ingredient ha-1 inhibited the growth of two of the 15 genotypes. Chlorophyll fluorescence intensity showed high levels of inhibition 3 h after treatment in chickpea. For all the genotypes, photosynthetic activity was recovered 10 days after treatment. Fluorescence-induction curves revealed that pyridate inhibited photosynthetic electron transport in chickpea genotypes and Amaranthus blitoides faster than in Lolium rigidum. Photosynthesis in chickpea genotypes recovered more quickly than in Lolium rigidum, while Amaranthus blitoides died 3 days after treatment. Hill reaction assays concluded that CL9673 was the most phytotoxic pyridate metabolite. The order of phytotoxicity was CL9673 >> CL9673-N-Gly > CL9869 > pyridate > CL9673-O-Gly. These results support the idea that tolerance of chickpea to pyridate is due to degradation and detoxification of the herbicide.

This work studied the tolerance mechanisms of chickpea (Cicer arietinum L.) to pyridate, a post-emergence herbicide used in other crops such as maize, peanut and wheat. Foliar absorption of pyridate in chickpea was limited and occurred mainly during the first 24 h after treatment. Over 83% of the herbicide absorbed remained in the treated leaf 72 h after treatment. Twelve hours after herbicide treatment, 50% of the total herbicide applied was converted to CL9673-N-Gly, an intermediate metabolite essential in the activation of the pyridazine ring for following conjugations. The N-glycoside was conjugated to form more-polar metabolites, C1 and C2: C1 was identified as CL9673-N-Gly- glutathione; and C2 was identified as CL9673-N-Gly-cysteine. C1 appeared 3 h after treatment and reached a maximum of around 40% of recovered radioactivity 72 h later, while C2 appeared 24 h after treatment and reached a maximum of 10% 72 h later. Chickpea glutathione transferases do not seem to be involved in the formation of C1, thus the final amount of this conjugate mainly depends on the amount of N-glycoside formation in vivo.

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