Study On The Target-site Resistence Mechanism And Fitness Of Echinochloa Crus-galli To Penoxsulam From Rice Fields In Hubei

Echinochloa Beauv.is one of the main pernicious weeds in rice fields in China,and is a major factor in reducing rice yield.Penoxsulam,dichloroquinolinic acid,acetamiprid,prochloraz and bensulfuron are the most commonly used herbicides for Echinochloa spp.in the rice field.Penoxsulam is an acetolactate synthase（ALS）inhibitor,and the long-term single repeated use of penoxsulam has led to a gradual increase in resistance of Echinochloa spp.to penoxsulam.In this study,In this study,Echinochloa spp.seeds collected from 62 main rice production areas in Hubei in 2018.We used whole plant bioassay to investigate the resistance level of Echinochloa spp.populations to penoxsulam;the molecular biology technique was used to clarify the target resistance mechanism of Echinochloa crus-galli 18-WJJ-Ec populations to penoxsulam;the greenhouse pot method was used to preliminarily investigate the fitness cost of Echinochloa crus-galli 18-WJJ-Ec populations carrying the Trp-574-Leu mutation locus of ALS gene.A greenhouse pot method was used to initially investigate the suitability cost of penoxsulam-resistant Echinochloa crus-galli 18-WJJ-Ec populations.The results of the study are as follows:1.Resistance level of Echinochloa spp.to penoxsulam The results showed that there were 26 areas with Echinochloa spp.populations at risk of resistance and 36 areas at low risk of resistance to penoxsulam.The resistance levels of Echinochloa spp.18-HWMJ,18-WJJ and 18-JSZ populations to penoxsulam were determined by dose-response curves.The results showed that the ED₅₀ of penoxsulam was 22.31 g a.i.ha^-1 and14.34 g a.i.ha^-1 to 18-HWMJ and 18-WJJ populations,and 0.31 g a.i.ha^-1 to 18-JSZ.The Echinochloa spp.18-HWMJ and 18-WJJ had 71.97-fold and 46.26-fold resistance indices relative to the sensitive population 18-JSZ,respectively,which were high resistance level.2.The target resistance mechanism of Echinochloa crus-galli to penoxsulam The results showed that a Trp-574-Leu mutant was detected in both 18-WJJ-Ec and 18-HWMJ-Ec populations;the mutation site of 18-WJJ-Ec population was mainly on the ALS2 gene sequence copy,and the frequency of Trp-574-Leu mutation in its ALS2 gene sequence was 87.50%;the mutation site of 18-HWMJ-Ec population was mainly on the ALS1 gene sequence copy,and the frequency of Trp-574-Leu mutation in its ALS1 gene sequence was 82.86%.Amino acid site mutations are the main cause of resistance to penoxsulam in 18-HWMJ-Ec and 18-WJJ-Ec.Before treatment with penoxsulam,the ALS concentrations in both 18-HWMJ-Ec and 18-WJJ-Ec populations were higher than those in the sensitive Echinochloa crus-galli 18-NJ population,and the resistance indices of Echinochloa crus-galli 18-WJJ-Ec and 18-HWMJ-Ec populations were 8.94-fold and6.39-fold relative to the sensitive Echinochloa crus-galli 18-NJ population,the results showed that the development of resistance to penoxsulam in Echinochloa crus-galli 18-HWMJ-Ec and 18-WJJ-Ec populations was related to the increase of ALS concentration and the decrease of ALS sensitivity to penoxsulam.In addition,the expression of ALS genes in both Echinochloa crus-galli 18-WJJ-Ec and 18-HWMJ-Ec populations were significantly higher than that in 18-NJ population before and 1 d after penoxsulam treatment,which indicated the existence of target gene overexpression mechanism in both Echinochloa crus-galli 18-WJJ-Ec and 18-HWMJ-Ec populations.The overall results indicated that both 18-HWMJ-Ec and 18-WJJ-Ec populations had a target resistance mechanism to penoxsulam3.Fitness cost of penoxsulam-resistant Echinochloa crus-galli populations The results showed that the penoxsulam-resistant Echinochloa crus-galli populations 18-WJJ-Ec population had significantly higher plant height,above-ground fresh weight and spike number than the sensitive Echinochloa crus-galli 18-NJ population,and the peak seed germination rate of 18-WJJ-Ec population was earlier than that of the sensitive Echinochloa crus-galli 18-NJ population.The assimilation rate,stomatal conductance,transpiration rate and chlorophyll content of the Echinochloa crus-galli 18-WJJ-Ec population were not significantly different from those of the sensitive 18-NJ population.The results showed that emergence of resistance to penoxsulam increased the fitness of Echinochloa crus-galli growth rate and germination rate,but had no significant effect on the fitness of Echinochloa crus-galli assimilation rate,stomatal conductance,transpiration rate and chlorophyll content.