Abstract
ABSTRACT: Knowledge of the level of resistance of weed populations and the herbicides to which they survive is important for recommending suitable advice to farmers and allowing the selection of appropriate management strategies. Whole-plant dose response experiments were carried out to assess the resistance status of eight putative resistant Galium spurium L. populations and one G. aparine L. population, originating from northern Greece. High levels of resistance of both species to the ALS-inhibiting herbicides chlorsulfuron and tribenuron were found, while their susceptible populations were controlled. Three G. spurium (GS) populations showed additional cross-resistance to [florasulam + 2,4-D], whereas the remaining five resistant GS populations were controlled with [tribenuron + mecoprop-p], [florasulam + 2,4-D], and [florasulam + aminopyralid]. Also, [florasulam + fluroxypyr] was very effective against two resistant GS populations tested. DNA sequence alignment of the three GS populations (GS 1, GS 6, and GS 8) with cross-resistance to chlorsulfuron, tribenuron, and florasulam revealed a point mutation at Trp-574 (tryptophan-574), causing amino acid substitution by Leu (leucine). The G. aparine (GA) population showed cross-resistance to chlorsulfuron and tribenuron, but it was controlled with [tribenuron + mecoprop-p], [florasulam + aminopyralid], [florasulam + 2,4-D], and [florasulam + fluroxypyr]. The confirmed cross-resistance of both GS and GA species to chlorsulfuron and tribenuron in northern Greece is the first report of Galium spp. resistance to ALS-inhibiting herbicides in Europe. Finally, all populations (8 GS and 1 GA) that showed resistance to chlorsulfuron and tribenuron were controlled with the mixtures [tribenuron + mecoprop-p] and [florasulam + fluroxypyr].
Highlights
Galium spp., such as G. spurium and G. aparine, are annual broadleaf weeds with reproduction by seed (Malik et al, 1988). Both species are native to Eurasia, whereas G. aparine is native to North America (Malik et al, 1988; Defelice, 2002)
Galium aparine occurs in temperate zones and in high altitudes in the tropics (Holm et al, 1978), whereas G. spurium is widely distributed in Europe (Hanf, 1983)
The aim of this research was to examine whether: 1) the poor control of G. spurium and G. aparine in northern Greece can account for development of cross-resistance to acetolactate synthase (ALS)-inhibiting herbicides, 2) to clarify the genetic basis of resistance by sequencing the als gene, and 3) to determine the effectiveness of mixtures of ALS-inhibitors with auxin-type herbicides as alternatives for control of the studied populations, bearing different herbicide resistance traits due to various histories of exposure to ALS-inhibiting herbicides
Summary
Galium spp., such as G. spurium and G. aparine, are annual broadleaf weeds with reproduction by seed (Malik et al, 1988). Both species are native to Eurasia, whereas G. aparine is native to North America (Malik et al, 1988; Defelice, 2002). G. aparine is found in arable fields and native habitats, waste ground, fence rows, barnyards, and pastures (Moore, 1975). This weed can grow in various soil types, but it is mostly found in nutrient-rich, deep, loamy and clayey soils, containing humus, and moist habitats (Holm et al, 1978). G. spurium prefers dry and sunny habitats and does not tolerate shade (Malik et al, 1988)
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