Root-knot nematodes (RKNs) cause significant economic damage to crop plants, spurring demand for safe, affordable, and sustainable nematicides. A previous study by our research team showed that the combination of two nematicidal secondary metabolites (SMs) derived from Photorhabdus bacteria, trans-cinnamic acid (t-CA), and (4E)-5-phenylpent-4-enoic acid (PPA) have a synergistic effect against RKNs in vitro. In this study, we considered in planta assays to assess the effects of this SM mixture on the virulence and reproductive fitness of the RKN Meloidogyne incognita in a cowpea. Factorial combinations of five t-CA + PPA concentrations (0, 9.0, 22.9, 57.8, and 91.0 μg/ml) and two nematode inoculation conditions (presence or absence) were evaluated in 6-week growth chamber experiments. Results from this study showed that a single root application of the t-CA + PPA mixture significantly reduced the penetration of M. incognita infective juveniles (J2s) into the cowpea roots. The potential toxicity of t-CA + PPA on RKN-susceptible cowpea seedlings was also investigated. The effect of t-CA + PPA × nematode inoculation interactions and the t-CA + PPA mixture did not show significant phytotoxic effects, nor did it adversely affect plant growth parameters or alter leaf chlorophyll content. Total leaf chlorophyll and chlorophyll b content were significantly reduced (by 15 and 22%, respectively) only by the nematode inoculum and not by any of the SM treatments. Our results suggest that a single root application of a mixture of t-CA and PPA reduces M. incognita J2's ability to infect the roots without impairing plant growth or chlorophyll content.

中文翻译：

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光杆菌衍生的次生代谢物可减少豇豆根结线虫对根部的感染。

根结线虫 (RKN) 对农作物造成重大经济损失，刺激了对安全、负担得起和可持续的杀线虫剂的需求。我们研究小组之前的一项研究表明，来自光杆菌属细菌的两种杀线虫次级代谢产物（SM）的组合，即反式肉桂酸（t-CA）和（4E）-5-苯基戊-4-烯酸（PPA）在体外对 RKNs 具有协同作用。在这项研究中，我们考虑通过植物测定来评估这种 SM 混合物对豇豆中 RKN 根结线虫的毒力和繁殖适应性的影响。在为期 6 周的生长室实验中评估了五种 t-CA + PPA 浓度（0、9.0、22.9、57.8 和 91.0 μg/ml）和两种线虫接种条件（存在或不存在）的因子组合。这项研究的结果表明，t-CA + PPA 混合物的单根施用显着减少了南方根结线虫感染性幼虫 (J2s) 对豇豆根部的渗透。还研究了 t-CA + PPA 对 RKN 敏感豇豆幼苗的潜在毒性。t-CA + PPA × 线虫接种相互作用和 t-CA + PPA 混合物没有表现出明显的植物毒性作用，也没有对植物生长参数产生不利影响或改变叶子叶绿素含量。仅通过线虫接种，而非任何 SM 处理，叶片总叶绿素和叶绿素 b 含量显着降低（分别降低 15% 和 22%）。我们的结果表明，单根施用 t-CA 和 PPA 混合物可降低南方根结线虫 J2 感染根部的能力，但不会损害植物生长或叶绿素含量。