The response of weedy sunflower (Helianthus annuus L.) to nicosulfuron: An examination of vegetative parameters and acetolactate synthase activity

Abstract

Genetic and morphological interpopulation variability of weed species is often responsible for variable responses to herbicides. As weedy sunflower, an invasive form of Helianthus annuus L., possesses high morphological and genetic variability, very different responses of its populations to herbicides can be expected. This species is one of the dominant weed species in row crops, including maize, in many European countries in which nicosulfuron is intensively used for weed control. There are little available data about the response of this sunflower form to nicosulfuron or of the interpopulation variability of its response to other herbicides. The responses of three weedy sunflower populations to nicosulfuron were studied in field dose-response experiments, and acetolactate synthase (ALS) enzyme activity at different herbicide concentrations was determined in vitro. Interpopulation variability in the response to nicosulfuron was confirmed. Populations WS2 and WS3 were more that 20-fold and 30-fold less susceptible to nicosulfuron, respectively, than population WS1, based on fresh weight, whereas the differences were not so prominent based on other parameters, including plant height, leaf area and ALS activity, and ranged from 2 to 12-fold. [Projects of the Serbian Ministry of Education, Science and Technological Development, Grant no. III46008 and Grant no. 173018]

Effects of nicosulfuron on biological production of weedy sunflower (Helianthus annuus)

“…Namely, the period between sowing and sampling dates in 2008 was characterized by somewhat higher rainfall than the corresponding period of 2009. This is coinciding with previous studies which confirmed that environmental conditions significantly affected the activity and effects of post-emergence herbicides (Bozic et al, 2012(Bozic et al, , 2015bBožić et al, 2019). In conclusion, nicosulfuron was found to have a significant impact on weedy sunflower vegetative production (plant height, fresh weight and leaf area) and on some generative parameters (number of heads per plant, weight of seeds per plant and number of seeds per plant).…”

“…Therefore, fresh weight and leaf area were more sensitive parameters (all applied herbicide rates reduced these parameters more than 50%) than plant height. This is not consistent with findings reported by Abbas et al (2005) that plant height was the more sensitive parameter to some ALS-inhibiting herbicides than dry weight, but it is in accordance with the findings of Božić et al (2019) who reported that plant height was the least sensitive parameter for estimating weedy sunflower response to nicosulfuron, compared to fresh weight and leaf area. Effects of herbicides (nicosulfuron in this case) to seed production of non-target weed species are important because seed production in a single growing season determines the potential weed problems in subsequent years.…”

“…Bozic et al (2016) found that the recommended rate (40 g a.i. ha -1 ) of nicosulfuron reduced vegetative and generative production of this weed, and Božić et al (2019) confirmed variability in weedy sunflower population responses to the same herbicide. As those studies showed that the recommended nicosulfuron rate was only able to reduce plant growth and different vegetative and generative parameters, rather than cause mortality of weedy sunflower, the objective of this study was to examine the influence of different rates of that herbicide on biological production of weedy sunflower under field conditions.…”

“…There is no information about weedy sunflower effects on crop yield in Europe, but in America, weedy forms of sunflower reduce yields of corn by up to 64% (Deines et al, 2004) and yields of soybean by as much as 97% (Geier et al, 1996). Cultivation of herbicide-tolerant sunflower hybrids, which tolerate ALS-inhibiting herbicides (Bozic et al, 2012), may be accountable for a potential flow of genes responsible for crop hybrid tolerance to weedy populations (Bozic et al, 2015a;Božić et al, 2019), leading to the development of resistant weedy sunflower.…”

“…As weedy sunflower and Sorghum halepense are common dominant weeds in some Serbian maize fields, and nicosulfuron is known to be effective in controlling S. halepense (Baghestani et al, 2007;Nosratti et al, 2007), it is useful to know more about weedy sunflower response to that herbicide. To our knowledge, weedy sunflower response to herbicides in Europe has been rarely studied (Božić et al, 2011(Božić et al, , 2019Bozic, 2016). Bozic et al (2016) found that the recommended rate (40 g a.i.…”