Phytoalexin formation in apple roots responding to apple replant disease (ARD) soil

苹果是一种有价值的果树，但它的繁殖受到苹果再植病（ARD）的影响，导致茎和根的生长发育迟缓。其原因尚不清楚，但根际微生物群的变化似乎起着重要作用。最近，我们的合作伙伴在ARD土壤中观察到易感砧木M26植株的生物量下降和根系损伤，与热处理和γ辐照土壤中的根系相比。首次检测到ard感染根中联苯和二苯并呋喃植物抗菌素的出现。此外，我们还观察到，在离体生长的根中，经过激发剂处理的植物抗毒素向培养基中渗出，这表明这些化合物从ARD土壤中的根释放到根际。我们将研究各种体外培养的砧木基因型经过激发子处理后，其植物抗毒素产生的定性和定量差异。还将测试来自ARD土壤中丰富物种的激发子制剂。主要的植物抗毒素将被合成，并检查其对各种根际（微生物）生物的影响。这些影响预计会引起生物群落组成的变化。植物抗毒素对根的活性也被检测，揭示潜在的化感作用和自中毒。此外，还研究了植物抗毒素合成的时空调控。我们的研究结果将有助于理解由苹果生长引起的土壤的复杂变化，以及苹果种植在ARD土壤中时本身的复杂变化。

Apple is a valuable fruit tree, however, its propagation is affected by apple replant disease (ARD), which leads to stunted growth of shoots and roots. The causes are poorly understood but changes in the microbiome of the rhizosphere appear to play an important role. Recently, biomass decline and root damage have been observed by our cooperation partner in susceptible rootstock M26 plants in ARD soils, when compared to roots in heat-treated and gamma-irradiated soils. For the first time, occurrence of biphenyl and dibenzofuran phytoalexins in ARD-affected roots was then detected. In addition, we have observed exudation of the phytoalexins from elicitor-treated in vitro-grown roots to the culture medium, suggesting release of the compounds from roots in ARD soils to the rhizosphere. We will study various in vitro grown rootstock genotypes after elicitor treatment for qualitative and quantitative differences in their phytoalexin production. Elicitor preparations from abundant species in ARD soils will also be tested. The major phytoalexins will be synthesized and examined for their effects on various rhizosphere (micro)organisms. These effects are expected to cause changes in the biome composition. The activity of phytoalexins toward roots is also examined, revealing potential allelopathy and autotoxication. Furthermore, the temporal and spatial regulation of phytoalexin biosynthesis in ARD-affected roots is studied. Our results will contribute to understanding the complex changes in soils, caused by apple growth, and in apple itself when planted into ARD soils.