Evaluation of Herbicide Translocation In Grafted Watermelon Using Liquid Scintillation Spectrometry and Autoradiography

Watermelon grafting provides resistance to certain soilborne pathogens and may eventually act as an alternative to methyl bromide fumigation.  If watermelon grafting becomes popular in the United States, farmers will need to know which herbicides are safe to use on a grafted crop.  In an effort to understand herbicide response differences seen in field trials comparing grafted and non-grafted watermelon plants, a herbicide translocation study was conducted.  Grafted and non-grafted watermelon plants were treated with radiolabeled atrazine and glyphosate to examine herbicide translocation.  Treated plant material was subjected to liquid scintillation spectrometry to quantify the amount of radiolabeled herbicide in various portions of the plants.  Additionally, autoradiographs were created to allow for visualization of absorbed and translocated herbicide.  Plants were harvested at 24 and 72 hours after herbicide treatment.  No significant differences were observed when comparing herbicide distribution within grafted versus non-grafted plants using liquid scintillation spectrometry.  When examining autoradiographs, atrazine distribution appeared to be quite uniform across treatments.  As for the glyphosate treatments, autoradiographs appeared to exhibit some differences when comparing translocation between grafted and non-grafted plants for the 24 hour harvest.  However, no differences between grafted and non-grafted watermelon plants were noted when examining autoradiographs from treatments that allowed glyphosate to absorb and translocate for 72 hours.