Differential Atrazine Tolerance Within Cucumber (Cucumis sativus)

The cucumber ( Cucumis sativus L.) accession PI 390244 tolerated up to 0.56 kg/ha atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triazine] whereas most cultivars and accessions were killed by 0.14 kg/ha. The possible mechanisms for tolerance were investigated by comparing growth rates, effects on photosystem II in isolated chloroplasts, and differences in uptake and translocation of 14 C-atrazine between tolerant PI 390244 and the susceptible cultivar Marketmore 70. PI 390244 had significantly more leaf area than Marketmore 70, but less root biomass. Isolated chloroplast preparations from both cultivars were equally susceptible to the herbicide. Although PI 390244 absorbed more total 14 C-atrazine, it translocated less radioactivity from the roots. While the concentration of 14 C found in the PI 390244 roots was 10 to 30% greater than in Marketmore 70, the amount of radioactivity in the cotyledons, and first and second true leaves of Marketmore 70 were 53, 34, and 55% higher, respectively, after 48 h.