| Barnyardgrass (Echinochloa Beauv.) is one of the 18 most important weeds in the cropped area. It is an annual weed wildly in distribution, aggressively in competition, seriously damageable in crop production, especially to rice. Here the biology and the herbicide tolerance of eight species and variations of barnyardgrass were studied as follows:There were 5 species and 3 varietas of barnyardgrass which occurred in rice fields of Jiangsu Province. They are: Echinochloa crusgalli (L.) Beavu., Echinochloa Hispidula (Retz.) Nees., Echinochloa colonum (L.)Link, Echinochloa Caudate Rosev. , Echinochloa cruspavonis (H. B. K.) Schult and Echinochloa crusgalli (L.) var. mitis (Pursh) Peterm, Echinochloa crusgalli (L.) Beauv var. zelayensis (H. B. K.) Hitche, Echinochloa crusgalli var. austro-japonensis Ohwi. Ecrusgalli (L.) var.mitis (Pursh) Peterm, Ecrusgalli (L.) Beauv var. zelayensis (H. B. K.) Hitche and Ecrusgalli (L.) Beavu. occurred everywhere in Jiangsu, the importance value of Ecrusgalli (L.) Beavu. var. mitis (Pursh.) Peterro was higher than any other species and variations ofbarnyardgrass, and Ecrusgalli (L.) Beauv var. zelayensis (H. B. K.) Hitche mainly occurred in Lixiahe rice area, and Echinochloa crusgalli (L.) Beavu. mainly occurred in Taihu and coastland rice area. The frequency and importance value of Echinochloa colonum (L.) Link were the lowest.The reproductive capacity of ?crusgalli (L.) var. mitis (Pursh) Peterm was the highest in 8 species and variations of barnyardgrass, it was adapted to the rice field and had the highest tolerance to the herbicide, so the distribution of the species was the most broad. Ecrusgalli (L.) Beauv var. zelayensis (H. B. K.) Hitche and Ecrusgalli (L.) Beavu. was followed. Ecrusgalli var. austro-japonensis Ohwi and ?colonum (L.) Link had the lowestreproductive capacity and the lowest tolerance to the herbicide, so, the distribution was the narrowest. E. Caudate Rosev. and ?cruspavonis .(H.B.K.) Schult had high reproductive capacity, but didn' t adapted to rice and rape rotation field, so the distribution in Jiangsu was lower.Surgical cuts were used to induce germination of dormant barnyardgress caryopses. When removing only the caryopsis coat covering the coleoptile induced up to 57. 33% germination, 58. 66% germination for removed all caryopsis coat, and24. 67% when removing caryopsis coat covering the radicle. Dormancy of barnyardgress was not just caused by the mechanical resistance of the caryopsis coat.Pretilachlor didn't inhibit the germination of barnyardgrass seeds, but it could inhibit its growth. After the pretilachlor treatment, the leaf of barnyardgrass twisted in coleoptiles, the length of leaf cells and coleoptiles cells become shorter, and the number of lamellae of granule and stroma in chloroplast was higher than the control, and starches accumulated in chloroplast. Pretilachlor inhibited the a -amylases activities of barnyardgrass, so the transport of nutrition to embryo was obstructed, and the growth of barnyardgrass was inhibited. The various changes happened on the morphology and physiology could explain the different tolerances to the pretilachlor between different species and variations of barnyardgrass. After the pretilachlor treatment, the results showed that the control percentage of ?crusgalli (L.) Beavu. var. mitis (Pursh.) Peterm was the lowest, and it was the highest for E. colonum (L.) Link among the eight species and variations to barnyardgrass. It seemed that the E. crusgalli (L.) Beavu. var. mitis (Pursh.) Peterm had higher tolerance to the herbicide.After the acetochlor treatment, It seemed that the ?crusgalli (L ) Beavu. var. mitis (Pursh.) Peterm had higher tolerance to the herbicide than ?colonum (L.) Link. Observed result from micromorphology showed that the leaf surface of E. crusgalli (L.) Beavu. var. mitis (Pursh.) Peterm was similar with E. colonum (L.) Link, so it may be not the reason leading to the various tolerances among different species and variaties of barnyardgrass. The acetochlor treatment har...
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