| Barnyardgrass, Echinochloa crusgalli (L.) Beauv., as the premier harmful weed in rice fields, has a serious impact on rice production. There are the main areas of rice production for China in Hunan province, occurrence areas of E. crusgalli in rice fields are huge and its annual levels are serious. As a simplified cultivaltion method, direct-seeded rice is very popular for farmers. However, occurrence levels of E. crusgalli are higher because water management in seeded-direct rice fields is very extensive. Penoxsulam is an effective and safety herbicide to control E. crusgalli in rice fields especially for direct-seeded rice fields. But E. crusgalli has showed different levels of resistance to penoxsulam because of its application of long-term, single and over-dose. In order to clarify the resistance levels of E. crusgalli in rice fields in Hunan province to penoxsulam,334 samples of E. crusgalli in rice fields were collected from 13 regions such as Changde, Yuanjiang, Nanxian, and etc. in 2013 in the present study. A preliminary screening of the resistance levels of these samples to penoxsulam were conducted via a water culture method with label cards (WCMLC). Then the resistance levels of high-risk resistant samples (mortality?40%) to penoxsulam were determined via a conventional method of the whole plant (MWP). In addition, the activity differences of acetolactate synthase (ALS) and glutathione-S-transferases (GSTs) of 4 high-resistant biotypes and 1 susceptible biotype were investigated after penoxsulam treatment. The reason of E. crusgalli resistant to penoxsulam would be clarified from the biochemical levels in order to provide scientific reference for life extension of penoxsulam and reasonable management of resistant E. crusgalli. The main results of the present study are as follows:1. A preliminary screening of the resistance levels of 334 samples of E. crusgalli to penoxsulam were conducted via the WCMLC. The results showed that there were 47 high-risk resistant samples of E. crusgalli and its value was 14% of the total samples. There were 10% and 18% of the total samples for high-risk resistant samples in early-rice and late-rice fields, respectively, but there was zero in medium-rice fields in 2013. In geographical division, there was a highest value (53.85%) of high-risk resistant samples of E. crusgalli in Yuanjiang, followed by Changde (27.27%), Shaoshang (22.22%) and Hanshou (18.37%), less in Wangcheng (12.50%), Changsha (6.67%), Yiyang (4.35%) and Ningxiang (3.45%), zero in Xiangtan, Xiangxiang, Xiangyin, Nanxian and Zhuzhou.2. The resistance levels of 47 high-risk resistant samples of E. crusgalli to penoxsulam were determined via the MWP. The results showed that the range of resistance index of those samples was 2.22-300.87, the lowest resistance level was Z-YJ-5 biotype collected from the rice fields in 3 group, Fudong village, Caowei town, Yuanjiang city. The range of resistance factor of 31 samples was 11.07-77.27 and its value was 65.9% of the total samples. The Z-CD-06 (collected from the rice fields in Niuhuangan village, Hangongdu town, Changde city), Z-HS-25 (collected from the rice fields in 8 group, Fenglin village, Yazigang town, Hanshou city), Z-CD-33 (collected from the rice fields in 1 group, Luhuaping village, Shigongqiao town, Changde city) and Z-CD-45 (collected from the rice fields in 6 group, Huangniu village, Zhuzhou town, Changde city) biotypes had the highest resistance levels, their resistance indexes were 216.16?238.73?259.04 and 300.87, respectively, suggesting that the resistance levels of the most of high-risk resistant samples of E. crusgalli to penoxsulam belonged to medium resistance levels, but little samples were high resistance levels.3. The IC50 values of high resistant biotypes (Z-CD-06, Z-HS-25, Z-CD-33 and Z-CD-45) and susceptible biotype (S1) of E. crusgalli were 7.0136,7.2851,10.3262, 14.3219 and 1.7183 ?g a.i./L in vitro, respectively. There were significant difference (P< 0.05) in above five samples. The ALS activities of high resistant biotypes (Z-CD-06, Z-HS-25, Z-CD-33 and Z-CD-45) were inhibited and then could be recovered, but could not in S1 biotype in vivo.4. There was a trend of increase first and then decrease for GSTs activities of the above five biotypes of E. crusgalli after penoxsulam treatment. The metabolism of GSTs in resistant biotypes to penoxsulam was higher than that in susceptible biotype. The increased activity of GSTs in Z-CD-45 biotype was significantly higher than that in other biotypes, suggesting that the reason of E. crusgalli resistant to penoxsulam was maybe attributed to the enhanced metabolism of GSTs to penoxsulam. |
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