Bayer CropScience, Chesterfield, MO, USA.
Department of Agricultural Biology, Colorado State University, Wentzville, MO, USA.
Pest Manag Sci. 2021 Feb;77(2):795-804. doi: 10.1002/ps.6080. Epub 2020 Sep 28.
Precise quantification of the fitness cost of synthetic auxin resistance has been impeded by lack of knowledge about the genetic basis of resistance in weeds. Recent elucidation of a resistance-endowing IAA16 mutation (G73N) in the key weed species kochia (Bassia scoparia), allows detailed characterization of the contribution of resistance alleles to weed fitness, both in the presence and absence of herbicides. Different G73N genotypes from a segregating resistant parental line (9425) were characterized for cross-resistance to dicamba, 2,4-d and fluroxypyr, and changes on stem/leaf morphology and plant architecture. Plant competitiveness and dominance of the fitness effects was quantified through measuring biomass and seed production of three F lines in two runs of glasshouse replacement series studies.
G73N confers robust resistance to dicamba but only moderate to weak resistance to 2,4-D and fluroxypyr. G73N mutant plants displayed significant vegetative growth defects: (i) they were 30-50% shorter, with a more tumbling style plant architecture, and (ii) they had thicker and more ovate (versus lanceolate and linear) leaf blades with lower photosynthesis efficiency, and 40-60% smaller stems with less-developed vascular bundle systems. F mutant plants had impaired plant competitiveness, which can lead to 80-90% less biomass and seed production in the replacement series study. The pleiotropic effects of G73N were mostly semidominant (0.5) and fluctuated with the environments and traits measured.
G73N is associated with significant vegetative growth defects and reduced competitiveness in synthetic auxin-resistant kochia. Management practices should target resistant kochia's high vulnerability to competition in order to effectively contain the spread of resistance.
由于缺乏对杂草中抗性遗传基础的了解，合成生长素抗性的精确量化受到了阻碍。最近在关键杂草物种狗尾草（Bassia scoparia）中阐明了赋予抗性的 IAA16 突变（G73N），这使得在有或没有除草剂的情况下，能够详细描述抗性等位基因对杂草适应性的贡献。从一个分离出的抗性亲本系（9425）中鉴定出不同的 G73N 基因型，以研究其对二甲四氯、2,4-D 和氟草烟的交叉抗性，以及对茎/叶形态和植物结构的影响。通过在两个温室替代系列研究中测量三个 F 系的生物量和种子产量，量化了植物竞争力和适应性影响的优势。
G73N 赋予了对二甲四氯的强大抗性，但对 2,4-D 和氟草烟的抗性仅为中等至较弱。G73N 突变体植物表现出明显的营养生长缺陷：（i）它们的高度降低了 30-50%，植株结构呈翻滚状，（ii）叶片变厚，呈卵形（而非披针形和线性），叶片光合作用效率降低，茎的直径减小 40-60%，维管束系统发育不良。F 系突变体植物的植物竞争力受损，这可能导致在替代系列研究中生物量和种子产量减少 80-90%。G73N 的表型多效性大多为半显性（0.5），并随所测量的环境和性状而波动。
G73N 与狗尾草合成生长素抗性植株的明显营养生长缺陷和竞争力降低有关。管理措施应针对抗性狗尾草在竞争中的高脆弱性，以有效遏制抗性的传播。
