Abstract:

The study aims to clarify the sensitive baseline of the novel pyrimidine salicylic acid herbicide Luorouracridine to Echinochloa barnyard (Echinochloa crus-galli (L.) P. Beauv.), and reveal its cross-resistance relationship with the commonly used barnyard herbicide in paddy fields. This study adopted the whole-plant bioassay (stem and leaf spray method), and used 50 non-paddy field barnyard grass populations (to avoid the pressure of herbicide selection in paddy fields) as the subjects to determine the sensitive baseline. Seven resistant/sensitive populations, namely B162 (Cyhalofop-butylresistant population), B196 (Penoxsulam resistant population), B218 (Metamifop resistant population), B031, B172, B191 (Quinclorac resistant population), and the sensitive population B025, were used to analyze the cross-resistance. The research results show that: (1) sensitive baseline establishment: the GR50 value of fluoropyrimidine for inhibiting the fresh weight of 50 barnyard grass populations ranges from 2.7213 to 15.7766 g a.i/hm². By Shapiro-WilK test, its W=0.9722 and p=0.2832 > 0.05, conforms to the normal distribution. The average GR₅₀ value (7.6169±2.7941)g a.i./hm² can be used as the sensitive baseline of barnyard grass to fluracil. (2) Cross-resistance characteristics: Luorouracridine has significant positive cross-resistance with the ALS inhibitor herbicide Penoxsulam, which has the same mechanism of action. The barngrass populations B162 (RI=7.71) and B196 (RI=8.40) that showed low-level resistance to Penoxsulam had resistance indices of B162 (RI= 6.79) and B192 (RI=3.27), respectively, both indicating low-level resistance. However, it has no cross-resistance with agents that have different mechanisms of action (ACCase inhibitors such as Cyhalofop-butyland Metamifop, and hormone inhibitors such as Quinclorac).The barngrass populations that developed resistance to the above three agents (such as the Quinclorac resistant population B031, RI=13.01; the Metamifop resistant population B218, RI=3.42) all had resistance indices to flumacil < 2.0, indicating sensitivity. In conclusion, Luorouracridine can be used as an alternative agent in rice-growing areas resistant to Quinclorac, Cyhalofop-butyl, and Metamifop. However, it should be used with caution in rice-growing areas resistant to Penoxsulam. It is recommended to mix it with herbicides of different modes of action to delay the evolution of resistance in barnyard grass and extend the service life of the agent. The research conclusion provides a scientific basis for drug resistance monitoring and the rational application of drugs.

Key words: Echinochloa crus-galli (L.) P. Beauv., herbicide, Luorouracridine, cross-resistance, sensitive baseline, ALS inhibitor, resistance management, whole-plant bioassay.