Effects Of New Herbicide ZJ0273 On Plant Growth Of Brassica Napus And B. Rapa And Their Differential Tolerance Mechanisms

New post-emergence herbicide propyl 4-(2-(4.6-dimethoxypyrimidin-2-yloxy)benzylamino)benzoate (ZJ0273) was used to investigate its effect on the physiological and morphological responses of two oilseed Brassica species (Brassica napus cv. Zheshuang 758 and B. rapa cv. Xiaoyoucai). Different concentrations of ZJ0273 [viz.,0,10,100 (normal dose for rape) mg/L for lab experiments and 0,100,500,1000 mg/L for field experiments] were applied in this regard. Moreover, kinetics of chlorophyll fluorescence was used to develop a resistance monitoring system for the crops in a non-destructive, real-time and efficacious way. Furthermore, partial least square (PLS) method was used to develop a PLS model for the rapid determination of amino acids in oilseed rape leaves.To evaluate the tolerance of Brassica species against this new herbicide, two cultivars of rapeseed B. napus cv. Zheshuang 758 and B. rapa cv. Xiaoyoucai were tested by a foliar spray of ZJ0273 at the rate of 100,500 and 1000 mg/L. The results showed that both the species of Brassica were slightly affected by ZJ0273. Increasing level of ZJ0273 herbicide from 100 to 1000 mg/L increased the stress for the plants of both species as indicated by enhanced accumulation of malondialdehyde content. The activities of ALS and antioxidant enzymes (superoxide dismutase and peroxidase), soluble protein and sugar contents, photosynthetic system (SPAD value, photosynthetic rate and chlorophyll fluorescence) as well as the agronomic characters also declined consistently with each successive increase in ZJ0273 concentration. In general the plants treated with 100 mg/L ZJ0273 recovered from the herbicide stress after 28 days. B. napus showed more tolerance than B. rapa to the new herbicide.In order to study the effects of herbicide ZJ0273 on growth of root, different concentrations of ZJ0273 (viz.,0,10,100 mg/L) was applied. The results showed that B. napus is more tolerant than B. rapa under the stress of ZJ0273, however, the root activity of both the species of Brassica was negatively affected by herbicide. It also indicated that only a slight inhibition was observed in root growth of B. napus under 10 mg/L ZJ0273 stress. While the inhibition in B. rapa was relatively serious, especially for 100 mg/L treatment, the inhibiting rate of root length and number of root tips was more than 80%. It is worth mentioning that the absorbable capability of Fe was enhanced by 10 mg/L ZJ0273 treated in both the species of Brassica. However, the absorbable capability of other elements (including K, Ca, Mg, B) was inhibited severely.To develop a herbicide resistance monitoring system for the crops in a non-destructive, real-time and efficacious way, two cultivars of rapeseed Brassica napus cv. Zheshuang 758 and B. rapa cv. Xiaoyoucai were tested by a foliar spray of ZJ0273 at the rate of 100,500 and 1000 mg/L. Our study revealed that Fv/Fm, NPQ, Y (â…¡), and RLCs were significantly decreased with the herbicide stress and leaf age. However, the resistant B. napus started to recover after 5 days. Moreover, the dosage-inhibiting curves of Y (â…¡) and ETR suggested that the 500 mg/L was a safer dose for B. napus, which induced an approximately 20% inhibition in B rapa. These results showed that the parameters like Fv/Fm, NPQ, Y (â…¡) and ETR may be appropriate to detect herbicide toxicity and also seem to be the key factors to establish a prospective resistance monitoring system in the field herbicide bioassays. Moreover, our results also shows that the 2nd fully expanded leaf could reflect more accurately the toxicity of herbicide to the rapeseed plant.In another experiment, HCl hydrolysis-HPLC was used to evaluate the contents of total amino acids (TTA) and three branched-chain amino acids (Leucine, Isoleucine, Valine) in the leaves of B. napus cv. Zheshuang 758, which were treated with new herbicide ZJ0273 at 100,500 and 1000 mg/L having 7,14 and 28 days interval. The TAA contents varied in the range of 15.86-20.59 mg/100 mg, and a distinct gradual decrease was observed along with the increase of herbicidal stress and leaf senescence. Similar results were found with branched-chain amino acids content. It is worth emphasizing that lower level of ZJ0273 (100 mg/L) can enhance the resistance of oilseed rape against stress.Similar changes among different leaf positions were also found in other 14 amino acids, which are also from hydrolysis of protein. Among these amino acids, glutamic acid showed the highest content in protein, while cysteine was the lowest one, which also exhibited slight difference among several leaf positions. In order to develop the partial least squares (PLS) model for the rapid determination of amino acids, the method of PLS was used and some relevant and informative variables were selected. After these applications with the total of 248 samples, the relevant wavelengths corresponding to different amino acids and total amino acids content were successfully achieved to develop the PLS model for the rapid determination of amino acids in rapeseed.