Novel Candidate Genes Differentially Expressed in Glyphosate-Treated Horseweed (Conyza canadensis)

The evolution of herbicide-resistant weed species is a serious threat for weed control. Therefore, we need an improved understanding of how gene regulation confers herbicide resistance in order to slow the evolution of resistance. The present study analyzed differentially expressed genes after glyphosate treatment on a glyphosate-resistant Tennessee ecotype (TNR) of horseweed (Conyza canadensis), compared to a susceptible biotype (TNS). A read size of 100.2 M was sequenced on the Illumina platform and subjected to de novo assembly, resulting in 77,072 gene-level contigs, of which 32,493 were uniquely annotated by a BlastX alignment of protein sequence similarity. The most differentially expressed genes were enriched in the gene ontology (GO) term of the transmembrane transport protein. In addition, fifteen upregulated genes were identified in TNR after glyphosate treatment but were not detected in TNS. Ten of these upregulated genes were transmembrane transporter or kinase receptor proteins. Therefore, a combination of changes in gene expression among transmembrane receptor and kinase receptor proteins may be important for endowing non-target-site glyphosate-resistant C. canadensis.

Nutrient availability and pH level affect germination traits and seedling development of Conyza canadensis

Reducing pesticide application in agricultural land is a major challenge for the twenty-first century. Responses of weed seed’s germination and seedling’s early development to chemical soil conditions around the seed may be a promising way to aid weed control in a no-till system. Thus, the objective of this work was to test, under controlled conditions, whether different chemical conditions affect the germination and development of horseweed [Conyza canadensis (L.) Cronquist]. We used, as treatment, solutions containing different nutrients (P, K, Ca, and Mg), separately and in combination, and at two pH levels (4.8 and 6.5). Phosphorus alone inhibited horseweed seed germination at ~ 7 times while had ~ 4 times reduction in final germination percentage and germination speed index for both pH tested. Other nutrients tested had a no-effect in germination speed index compared to the control treatment. Potassium alone or associated with other ions (P, Ca, and Mg) at pH 4.8 had a synergistic effect on seedling development (root and shoot length). In the same way, K associated with Mg was synergistic to the root length at pH 6.5. Seeds in the control treatment (distilled water) presented a high germination speed index at pH 6.5, while at low pH this parameter was higher when in association with KMg, PMg and Ca. The findings demonstrate that seed germination traits and seedling development of horseweed depend on nutrient kind exposure and pH conditions in the seed environment. This work suggests that adequate topsoil management (i.e., pH and nutrient availability) may aid to reduce weed germination, because, it consists of an important factor of weed occurrence in agricultural areas.

A survey evaluating the spatial and temporal distribution of horseweed (Conyza canadensis) late season in Ohio soybeanfields from 2013 to 2017

On-site surveys of weed populations provide information on the relative occurrence and density of weeds that can be useful to growers in that region. Data generated by weed surveys can aid in the management of weed issues by monitoring the movement of problem weeds and forecasting areas susceptible to infestations. Currently, on-site surveys are often performed on a small scale, within single fields or counties. Questionnaire surveys are helpful for assessing relative abundance, but don’t always provide detailed information on weed distribution in time or space. A survey was conducted annually in Ohio from 2013 through 2017 in 49 counties with soybean [Glycine max (L.) Merr.] production to assess the late-season occurrence of horseweed [Conyza canadensis (L.) Cronquist]. The objectives of this research were to: 1) determine the frequency, level of infestation, and distribution of C. canadensis in soybean fields in the primary soybean-producing Ohio counties over five years; 2) identify significant spatial clusters or movement trends over time. Conyza canadensis was encountered in each county from 2013 through 2017. Spatial cores of interest, or counties identified as having significant levels of C. canadensis infestations or a lack thereof, relative to surrounding counties, were identified in all years except 2017. The lowest frequency of C. canadensis encountered at all rating levels occurred in 2017, which coincided with second highest frequency of infestations (highest density level) among years. There was no distinct distribution or pattern of C. canadensis movement within the state from year to year, but there was an increase in counties with infestations over time compared to the early years of the survey where many counties had few to no infestations. These results suggest that C. canadensis persists as a common and troublesome threat to Ohio soybean producers, and that growers should continue making C. canadensis management a priority when developing weed control programs.

Control of glyphosate-resistant horseweed (Conyza canadensis L.) with tiafenacil mixes in corn

Four field experiments were completed in commercial corn fields during 2019 and 2020 to determine glyphosate-resistant (GR) horseweed control in corn with tiafenacil alone or in combination with bromoxynil, dicamba, or tolpyralate applied preplant (PP). Corn planted 1 to 10 d after herbicide application was not injured with any of the herbicides tested. GR horseweed interference reduced corn grain yield 32% when left uncontrolled. Herbicides reduced GR horseweed interference and resulted in corn grain yield that was similar to the weed-free control. Glyphosate (900 g ae ha−1) + tiafenacil at 12.5, 25, and 37.5 g ha−1 controlled GR horseweed 63, 68, and 72% at 4 weeks after treatment (WAT) and decreased GR horseweed density 64, 43, and 83%, and dry biomass 69, 55, and 83%, respectively. Glyphosate + tiafenacil at 12.5, 25, and 37.5 g ha−1 plus bromoxynil (280 g ai ha−1) controlled GR horseweed 81, 88, and 87% at 4 WAT, and reduced GR horseweed density 82, 94, and 93% and dry biomass 93, 93, and 98%, respectively. Glyphosate + tiafenacil at 12.5, 25, and 37.5 g ha−1 plus dicamba (300 g ai ha−1) controlled GR horseweed 86, 88, and 88% at 4 WAT and decreased GR horseweed density 76, 89, and 86% and dry biomass 94, 98, and 98%, respectively. Glyphosate + tiafenacil at 12.5, 25, and 37.5 g ha−1 plus tolpyralate (30 g ai ha−1) controlled GR horseweed 90, 90, and 91% at 4 WAT and decreased GR horseweed density 93, 91, and 95% and dry biomass 98, 97, and 97%, respectively. The industry standards in Ontario, glyphosate + dicamba/atrazine and glyphosate + saflufenacil/dimethenamid-p controlled GR horseweed 95 and 100% at 4, 8 and 12 WAT and caused a 99 and 100% density or biomass reduction, respectively.

Ethno - Botanical Survey Of Plant Species Used For Mosquito Control In Nigeria

In Nigeria, there is paucity of information on plants used to repel or kill mosquitoes despite the abundant plant species in the country’s tropical rain forests. Majority of available data are on the traditional use of plants for curative purposes. This study documents some plant species used for insecticidal or repellent purposes against mosquitoes in Nigeria. An ethno-botanical survey was carried out in four geo-political zones in the country using structured questionnaires and focus group discussion. A total of six plant species belonging to five families were reported in Delta state with Conyza Canadensis (Compositae) being the most utilized (50%) and Aspilia africana (Compositae), the least mentioned (5.60%). In Enugu state, a total of nine plant species belonging to eight families were mentioned by respondents with Aframomum melegueta the most utilised (26.09%) while Agava sisalana and Dracaena manii belonging to the families Agavaceae and Dracaenaceae were the least mentioned (1.09% each). A total of six plant species belonging to five families were reported in Kaduna State with Lantana camara belonging to the family Verbenaceae accounting for 58.82% of the utilised plant species for mosquito control while Ipomea asarifolia, Terminalia catappa and Citrullus vulgaris belonging to the families Convolvulaceae, Combretaceae and Cucurbitaceae respectively were the least utilized (5.88% each). Lagos State recorded the highest number of plant species (twenty five) belonging to eighteen families. Spondia mombin belonging to the family Lilaceae was the most mentioned (7.33%) while the least mentioned (0.37% each) were Magnifera indica, Baphia nitida and Pennisetum purpeum belongingto the families Anacardiaceae, Fabaceae and Poaceae respectively. There is a need for further investigation on these plant species as they may constitute potential sources of cidal and repellent compounds against a wide range of insect pests. Keywords: Ethno-botanical survey, insecticidal, repellence, mosquitoes, plant species

Environmental cues affecting horseweed (Conyza canadensis) growth type and their sensitivity to glyphosate

Horseweed [Conyza canadensis (L.) Cronquist] is a facultative winter annual weed that can emerge from March to November in Michigan. Fall emerging C. canadensis overwinters as a rosette, while spring emerging C. canadensis skips the rosette stage and immediately grows upright upon emergence. In Michigan, primary emergence recently shifted from fall to spring/summer and therefore from a rosette to an upright growth type. Growth chamber experiments were conducted to determine 1) whether both C. canadensis growth types could originate from a single parent and 2) if common environmental cues can influence growth type. Variations in temperature, photoperiod, competition, shading, and soil moisture only resulted in the rosette growth type in four C. canadensis populations originating from seed collected from a single parent of the upright growth type. However, a vernalization period of four weeks following water imbibition, but prior to germination, resulted in the upright growth type. Dose-response experiments were conducted to determine whether glyphosate sensitivity differed between C. canadensis growth types generated from a single parent of the upright growth type. Upright type C. canadensis from known glyphosate-resistant populations ISB-18 and MSU-18 were four and three-fold less sensitive to glyphosate than their rosette siblings, respectively. Interestingly, differences in glyphosate sensitivity was not observed between growth types from the susceptible population. These results suggest that while C. canadensis populations shift from winter to summer annual lifecycles, concurrent increases in glyphosate resistance could occur.