The seed-associated microbiome of cactus and its implications for plant health

The Cactaceae is a family of plants characteristic of arid and semi-arid environments. Despite being highly resistant to different types of stress, their populations are drastically affected due to over-collection and severe perturbation of their habitat. One of the riskiest stages in the reproduction of cactus is the germination of seeds, although there is evidence that indicates the relevance of the seed-associated microbiome during this stage, little is known about its structure and function. In this work, we explore the diversity of the microbial community associated with seeds of four cactus species that have some type of exploitation either for ornamental use, and edible fruits and stems (Echinocactus platyacanthus, Ferocactus latispinus, Ferocactus pilosus and Stenocereus queretaroensis). For this purpose, Illumina sequencing of the 16S rRNA gene for Bacteria and the ITS1/ITS4 region for fungi was performed, as well as the isolation of cultivable microorganisms and the characterization of their plant growth-promoting capacities. We determine that bacterial communities associated with cactus seeds possess high richness but are dominated by few taxa, and in most cases, there are clear differences between episeminal and endoseminal communities, especially for fungi. The cactus seed microbiota is composed of a mix of potential pathogens and beneficial microorganisms, that could influence the germination percentage and the seedlings development. This phenomenon could be related to the health, principally by the growth-promoting abilities, the protection against pathogens in the early stages of plant development, in addition to nitrogen fixation, chitinolytic activity, and phytohormones production.