Biological Control of Root-Knot Nematode Meloidogyne incognita Infection of Tomato (Solanum lycopersicum L.) by the Oomycete Biocontrol Agent Pythium oligandrum

The biocontrol agent Pythium oligandrum, which is a member of phylum Oomycota, can control diseases caused by a taxonomically wide range of plant pathogens, including fungi, bacteria, and oomycetes. However, whether P. oligandrum could control diseases caused by plant root-knot nematodes (RKNs) was unknown. We investigated a recently isolated P. oligandrum strain GAQ1, and the P. oligandrum CBS530.74 strain, for the control of RKN Meloidogyne incognita infection of tomato (Solanum lycopersicum L.). Initially, P. oligandrum culture filtrates were found to be lethal to M. incognita second-stage juveniles (J2s) with up to 84% mortality at 24 h after treatment compared to 14% in the control group. Consistent with the lethality to M. incognita J2s, tomato roots treated with P. oligandrum culture filtrates reduced the attraction of nematodes, and the number of nematodes penetrating the roots was reduced by up to 78%. In a greenhouse pot trial, P. oligandrum GAQ1 inoculation of tomato plants significantly reduced the gall number by 58% in plants infected with M. incognita. Notably, P. oligandrum GAQ1 mycelial treatment significantly increased tomato plant height (by 36%), weight (by 27%), and root weight (by 48%). Transcriptome analysis of tomato seedling roots inoculated with the P. oligandrum GAQ1 strain identified ~2,500 differentially expressed genes. The enriched GO terms and annotations in the up-regulated genes suggested modulation of plant hormone-signaling and defense-related pathways in response to P. oligandrum. In conclusion, our results support that P. oligandrum GAQ1 can serve as a potential biocontrol agent for M. incognita control in tomato. Multiple mechanisms appear to contribute to the biocontrol effect involving direct inhibition of M. incognita, potential priming of tomato plant defenses, and plant growth promotion. Overall design: Triplicate sets of pooled tomato seedling roots grown in Petri dishes with or without Pythium oligandrum GAQ1.

生防因子（biocontrol agent）寡雄腐霉（Pythium oligandrum）隶属于卵菌门（Oomycota），可防控分类学跨度广泛的多种植物病原菌引发的病害，涵盖真菌、细菌及卵菌。然而，寡雄腐霉是否能够防控植物根结线虫（root-knot nematodes，RKNs）引发的病害，此前尚无定论。
本研究针对新近分离的寡雄腐霉菌株GAQ1，以及CBS530.74菌株，探究其对番茄（Solanum lycopersicum L.）受南方根结线虫（Meloidogyne incognita）侵染的防控效果。初始实验发现，寡雄腐霉培养滤液对南方根结线虫二龄幼虫（second-stage juveniles，J2s）具有致死活性：处理24小时后，线虫死亡率最高可达84%，而对照组仅为14%。
与该致死效应相一致，经寡雄腐霉培养滤液处理的番茄根系可降低线虫的趋化性，且穿透根系的线虫数量最多减少78%。在温室盆栽试验中，接种寡雄腐霉GAQ1的番茄植株，其受南方根结线虫侵染后的虫瘿数量显著降低58%。值得注意的是，寡雄腐霉GAQ1菌丝处理可显著提升番茄株高（增幅36%）、植株鲜重（增幅27%）及根系鲜重（增幅48%）。
对接种寡雄腐霉GAQ1的番茄幼苗根系进行转录组分析，共鉴定出约2500个差异表达基因。上调基因富集的基因本体（Gene Ontology，GO）术语及注释结果显示，寡雄腐霉处理可调控植物激素信号通路与防御相关通路。
综上，本研究结果证实，寡雄腐霉GAQ1可作为防控番茄南方根结线虫的潜在生防因子。其生防效应可能通过多种机制实现：直接抑制南方根结线虫、潜在预激活番茄植株的防御系统，以及促进植物生长。
实验整体设计：设置三组生物学重复，每组均为培养于培养皿中、分别接种或不接种寡雄腐霉GAQ1的番茄幼苗混合根系。