HARNESSING THE MICROBIOME OF VERMI-COMPOST TO PROTECT SOLANUM LYCOPERSICUM AGAINST FUSARIUM WILT

Tomato (Solanum lycopersicum L.) is consumed globally as a fresh vegetable. It is highly nutritional and has antioxidant properties. However, soil-borne diseases such as bacterial wilt and Fusarium wilt can significantly reduce its yield and quality. The use of agrochemicals to combat these diseases can produce chemical residues, pesticide resistance, and environmental pollution. Alternative protection strategies are thus needed. One of the most promising solutions is to harness microbial communities that can inhibit disease and promote plant growth and immunity. Most suppressive soils lose their activity when sterilized, which is strong evidence of the important role played by soil microorganisms in pathogen suppression. An agricultural practice that can enhance this microbiological activity is the addition of compost, an organic soil amendment with suppressive properties against several soil-borne pathogens, including Fusarium spp. This study evaluated the impact of vermi-compost on the growth of tomato and its possible suppressive effects on phytopathogen Fusarium oxysporum f. sp. lycopersici (Fol). It also sought to gather information about the microbial community residing in the compost. To study plant growth, vigor parameters (stem length, fresh weight, dry weight, water content and fluorescence intensity) were analyzed in seedlings after they had been growing for 21 days in mixtures of sterile and non-sterile substrates. The ability of the compost to suppress the phytopathogen was studied in vitro with bacterial and fungal isolates through a plate inhibition assay, and in vivo by inoculating Fol on the 21-day-old seedlings. The presence of 30% compost in the growth mixture allowed for greater plant development, growth and use of nutrients. Likewise, the compost reduced the severity of disease in the seedings by 12%. Scanning electron microscopy was used to study the mycoparasitic activity of a Trichoderma sp. isolated from the compost against Fol. Bacterial isolates, on the other hand, were identified with three molecular markers: 16S ribosomal RNA, DNA gyrase subunit A (gyrA), and RNA polymerase beta subunit (rpoB). Both a Bacillus sp. and the Trichoderma sp. were capable of inhibiting the growth of the pathogen. These findings confirm the suppressiveness of the compost and the PGPR aptitudes of the residing microorganisms. The complete isolated genome of the bacterial species will be elucidated in the context of a project approved to be part of GetGenomes GGLatAm2024 initiative. Moreover, the cyclic lipopeptides generated by this species will be studied by HPLC-mass spectrometry.

番茄（Solanum lycopersicum L.）是全球范围内作为鲜食蔬菜广泛消费的作物，兼具较高营养价值与抗氧化活性。然而，青枯病、尖孢镰刀菌枯萎病等土传病害会显著降低其产量与品质。使用农用化学品防治此类病害易引发化学残留、抗药性及环境污染问题，因此亟需开发替代防控策略。其中最具潜力的方案之一，是利用能够抑制病害、促进植物生长与免疫的微生物群落。多数具有抑病能力的土壤经灭菌后会丧失其抑病活性，这为土壤微生物在病原菌抑制过程中发挥的关键作用提供了有力佐证。可增强该微生物调控活性的农艺措施之一是施加堆肥——堆肥是一类对包括镰刀菌属（Fusarium spp.）在内的多种土传病原菌具有抑病效果的有机土壤改良剂。本研究评估了蚯蚓堆肥（vermi-compost）对番茄生长的影响，及其对植物病原菌尖孢镰刀菌番茄专化型（Fusarium oxysporum f. sp. lycopersici，简称Fol）的潜在抑病作用，同时解析了堆肥中栖息的微生物群落组成信息。为研究植物生长情况，研究人员将幼苗接种于无菌与非无菌基质的混合体系中培养21天后，分析其生长活力参数（茎长、鲜重、干重、含水量及荧光强度）。针对堆肥的抑病能力，研究人员通过平板抑菌试验，对分离得到的细菌与真菌菌株开展体外活性验证；同时以21日龄幼苗接种Fol，开展体内抑病效果评估。实验结果显示，生长基质中添加30%的堆肥可显著促进植株生长发育与养分吸收利用。与此同时，该堆肥可将幼苗的病害严重程度降低12%。研究人员借助扫描电子显微镜，观察了从堆肥中分离得到的木霉菌属（Trichoderma sp.）菌株对Fol的重寄生活性。另一方面，研究人员采用3种分子标记对细菌分离物进行鉴定：16S核糖体RNA（16S ribosomal RNA）、DNA促旋酶A亚基（DNA gyrase subunit A，简称gyrA）以及RNA聚合酶β亚基（RNA polymerase beta subunit，简称rpoB）。芽孢杆菌属（Bacillus sp.）与上述木霉菌属菌株均能有效抑制病原菌的生长。上述研究结果证实了该堆肥的抑病性，以及其中栖息微生物的植物根际促生菌（Plant Growth Promoting Rhizobacteria，简称PGPR）特性。本研究分离得到的该细菌菌株的完整基因组，将在获批纳入GetGenomes GGLatAm2024计划的项目框架内完成解析。此外，该菌株产生的环脂肽类物质将通过高效液相色谱-质谱联用（HPLC-mass spectrometry）开展后续研究。