生物测定法测定苎麻园小飞蓬对草甘膦的抗药性试验

为了明确湖南省主要苎麻产区小飞蓬对草甘膦的抗药性情况,在采集各地麻园小飞蓬种子的基础上,采用温室生物测定法测定了其对草甘膦的抗药性水平。试验结果表明:采自南县、汉寿、君山、华容、慈利、永定、永顺和吉首等地的小飞蓬种群的相对抗药性倍数均低于2,而采自沅江、湖南农业大学苎麻基地以及桃源等3地小飞蓬种群相对抗药性倍数较高,其中沅江小飞蓬种群相对抗药性倍数达到了3.49,这说明在湖南省主要苎麻产区,部分地区的小飞蓬种群已经产生了对草甘膦的抗药性。     

Reduced translocation is involved in resistance to glyphosate and paraquat in Conyza bonariensis and Conyza canadensis from California

Resistance to glyphosate and paraquat has evolved in some populations of Conyza spp. from California, USA. This study evaluated whether herbicide absorption and translocation were involved in the mechanism of resistance to both herbicides. Three lines of each species were used: glyphosate‐paraquat‐susceptible (GPS), glyphosate‐resistant (GR) and glyphosate‐paraquat‐resistant (GPR). Radiolabelled herbicide was applied to a fully expanded leaf, and absorption and movement out of the treated leaf were monitored for up to 24 h for paraquat and 72 h for glyphosate. Plants treated with paraquat were incubated in darkness for the first 16 h and then subjected to light conditions. More glyphosate was absorbed in C. bonariensis (52.9–58.3%) compared with C. canadensis (28.5–37.6%), but no differences in absorption were observed among lines within a species. However, in both species, the GR and GPR lines translocated less glyphosate out of the treated leaf when compared with their respective GPS lines. Paraquat absorption was similar among lines and across species (71.3–77.6%). Only a fraction of paraquat was translocated in the GPR lines (3% or less) when compared with their respective GPS or GR lines (20% or more) in both species. Taken together, these results indicate that reduced translocation is involved in the mechanism of resistance to glyphosate and paraquat in C. bonariensis and C. canadensis.     

Comparing after-ripening response and germination requirements of Conyza canadensis and C. bonariensis (Asteraceae) through logistic functions

Germination requirements and after‐ripening effects during one year of dry storage at 15/5 and 25/15°C (day/night) were compared for Conyza bonariensis and C. canadensis (Asteraceae). A logistic function was fitted to the results from tests over time in various incubation conditions, using three populations of each species as replicates. Time required for response to dry storage was measured by using a new method, the third derivative of the logistic function. Therefore, a point when major germination was achieved could be detected, without having to rely on maximum germination (which is uncertain), individual data points or any subjectively chosen limit. Fresh seeds of both species were dependent on light for germination and after‐ripening was mainly manifested by increasing germination in darkness. Low dormancy status and light requirement might indicate that soil cultivations should rapidly reduce the seedbanks of these species, although fecundity and wind dispersal will affect population levels. The species differed in their germination response, with C. bonariensis germinating at lower temperatures than C. canadensis. This seemingly counter‐intuitive result may explain the prevention of fatal germination of C. canadensis in cold conditions and its behaviour as a summer annual in northern climates, while C. bonariensis is restricted to warmer parts of the world.     

Saflufenacil efficacy on horseweed and its interaction with glyphosate

Saflufenacil is a new herbicide on the market and its effectiveness on horseweed, several populations of which have evolved resistance to glyphosate, is not clear. In this research, the effect of adjuvants on the control of horseweed with saflufenacil in the field, the effect of the interaction between glyphosate and saflufenacil on glyphosate‐resistant and glyphosate‐susceptible horseweed and the patterns of uptake and translocation of glyphosate applied alone and in combination with saflufenacil in horseweed were evaluated. The addition of methylated seed oil to saflufenacil provided the best control of horseweed, with crop oil concentrate being intermediate in effect and non‐ionic surfactant ranking as the least‐effective adjuvant. The interaction between glyphosate and saflufenacil was additive with regards to the control of glyposate‐resistant horseweed. The glyphosate‐susceptible horseweed population absorbed 6–13% more ¹⁴C‐glyphosate than the glyphosate‐resistant population. The addition of saflufenacil reduced ¹⁴C‐glyphosate translocation in both the glyphosate‐resistant and the glyphosate‐susceptible horseweed populations by at least 6%; however, due to the exceptional efficacy of saflufenacil, these reductions did not reduce the level of control. Saflufenacil holds great potential as an alternative control option for glyphosate‐resistant horseweed and is a valuable tool in the management of resistant weeds.     

Allelopathic Effect of Conyza albida on Avena sativa and Spirodela polyrhiza

The allelopathic influence of four plant tissues of Conyza albida (stems, leaves and inflorescences) on oat growth were investigated using in vivo tests. Oat growth (fresh and dry weights of above and underground parts) was inhibited from phytotoxic activity of upper leaves and inflorescence tissues of C. albida in pot studies. The inhibition was significantly higher than in the other tissues studied. The inhibiting action of crude extracts and volatile compounds from young plants (rosette) and mature plants were examined using two bioassay methods: (a) seed germination and radicle growth of oat and (b) fresh weight of duckweed plants. Both bioassayed species exhibited greater phytotoxic response from the young plants, collected in winter, than from the mature ones.