Conyza sumatrensis: A new weed species resistant to glyphosate in the Americas

Abstract

Recent reports of weed‐control failures after the use of glyphosate led to suspicion about the selection of resistant biotypes of Conyza at locations in west and north Paraná, Brazil. Plants were collected, identified as Conyza sumatrensis and subsequently evaluated for possible resistance to glyphosate in four stages of weed development. The experiments were carried out in a greenhouse by combining biotypes, stages of development and a range of glyphosate doses. All the suspected biotypes were collected from locations in Cascavel, Toledo, Assis Chateaubriand, Tupãssi and Campo Mourão with a history of glyphosate use in burndown and in glyphosate‐resistant soybean for at least the four previous years and were compared to a susceptible biotype (São Jorge do Ivaí) with no previous history of herbicide use. The doses of glyphosate ranged from 0 to 5760 g ae ha−1. The biotypes were considered as resistant if two combined criteria were present (resistance factor > 1 and the rate required to achieve 80% control is >720 g ha−1). The results provided evidence that there is a marked difference in the level of control of older plants and also confirmed the presence of some resistant biotypes. For applications at the first stage of development, two biotypes that were resistant to glyphosate were identified (Cascavel‐1 and Tupãssi‐6). For applications in the second stage of development, beyond the biotypes that were found in the first stage, three other biotypes were considered as resistant: Toledo‐5, Assis Chateaubriand‐7 and Floresta‐10. However, for applications at the third and fourth stages, all the biotypes were considered as resistant.

<b>Genetic admixture in species of <i>Conyza</i> (Asteraceae) as revealed by microsatellite markers

“…In the samples of C. sumatrensis distributed among the six sites from southern Brazil (Paraná State), the highest proportion of polymorphic loci (83.3%) was observed in samples from Campo Mourão and Cafelândia. However, the highest number of alleles (Na = 2.0833) and the highest effective number of alleles (Ne = 1.8016), as well as the highest mean expected heterozygosity value (H e = 0.3632), were observed in the samples from Toledo-R identified by Santos et al (2014b) as resistant to glyphosate (Table 5). A high number of alleles (Na = 1.9167) and a high effective number of alleles (Ne = 1.6171) were also observed in samples of resistant biotypes from Cascavel-R (Table 5).…”

“…Conyza bonariensis and C. sumatrensis are common in Southern, Southeast and Midwestern of Brazil (Santos et al, 2014b). In contrast, C. canadensis occurs only in the Southern Region, particularly in Rio Grande do Sul State (Lazaroto et al, 2008).…”

Invasion by Conyza sumatrensis alters soil microbial community structure in urban ecosystems

“…sumatrensis, native to South America (Anastasiu and Memedemin 2011;Santos et al 2014aSantos et al , 2014b, commonly known as tall fleabane or broad-leaved fleabane, is a cosmopolitan species and is found frequently in abandoned fields, roadsides, and waste areas (Hao et al 2009). It is widespread throughout the USA, Western Europe, and around the Mediterranean Basin (Thebaud and Abbott 1995) and also occurs in central Africa, Australasia, Central America, and Japan (Sansom et al 2013).…”

“…The rapid range expansion of this ruderal species locally may be attributed to the production of a large number of small, wind-dispersed seeds, ranging to over 200,000 seeds per plant (Sansom et al 2013), high resistance to diseases, herbivory, and herbicides (Santos et al 2014a(Santos et al , 2014b. It is pertinent to mention that recent transcontinental comparison of the impact of Conyza based on field studies, greenhouse experiments, and individualbased models revealed its strong suppressive impact on native plant diversity in non-native regions but not at home (Shah et al 2014a).…”

Fall management of fleabane based on glyphosate+2, 4-D, MSMA and glufosinate applied isolated or in tank mixture with residual herbicides

“…In Brazil, glyphosate-resistant Conyza bonariensis and C. canadensis were first reported in 2006 both in citrus orchards located in São Paulo State (Moreira et al, 2007) and in grain-producing areas in Rio Grande do Sul (Vargas et al, 2007). Besides that, resistant biotypes of Conyza sumatrensis were also reported in Paraná State (Santos et al, 2014).…”