Root rot in carnations (Dianthus caryophyllus) is a devastating condition primarily caused by soil-borne fungal pathogens, most notably those from the genera *Fusarium*, *Pythium*, and *Rhizoctonia*. From the plant's perspective, this is a systemic attack that begins at the foundation of its existence—the root system. The roots are responsible for water and nutrient uptake, anchorage, and storing essential compounds; their compromise leads to a cascade of physiological failures.
From my perspective as a carnation plant, the attack begins when fungal spores, resting in the soil, detect the exudates from my young or damaged roots. They are attracted to this chemical signal and germinate, directly invading my root tissues. *Pythium* species, for example, produce motile zoospores that swim through water-filled pores in the soil towards me. Once they make contact, they form structures that penetrate my cell walls. Inside, the fungi proliferate, feeding on my cell contents and effectively blocking my vascular system, the xylem and phloem. This is the critical first stage where my vital supply lines are severed.
As the fungi colonize my root cortex and vascular tissues, I face an internal crisis. The physical blockage of my xylem vessels means I cannot transport water and dissolved minerals from my roots to my stem and leaves. Even if the growing medium is wet, I begin to experience severe physiological drought. My leaves start to wilt, not from a lack of water in the soil, but because I cannot move it upwards. Simultaneously, the transport of sugars and energy produced by photosynthesis in my leaves down to my roots via the phloem is also disrupted. This starves my remaining healthy root tissues, weakening me further and making me more susceptible to continued invasion.
My internal struggle becomes visibly apparent. The first sign I show is a wilting of my lower leaves and stems, which may be mistaken for simple thirst. However, unlike under-watering, the soil will remain moist. As the rot progresses, my foliage turns from a healthy green to a dull, yellow-grey, and my growth becomes severely stunted. The most telling sign is at my base; my stem may become soft, brown, and water-soaked. If you were to gently uproot me, instead of a firm, white, healthy root system, you would find roots that are brown-to-black, mushy, and easily slough off. This is the visual evidence of the extensive tissue death occurring below the surface.
To avoid this fate, my needs are specific. I require a well-draining growing medium that provides both moisture retention and ample aeration. My roots need oxygen to perform respiration and function correctly; waterlogged, compacted soil suffocates me, causing root cells to die and creating the perfect anaerobic environment for root rot fungi to thrive. I prefer to be watered deeply but infrequently, allowing the top layer of the medium to dry out between waterings. Furthermore, I am highly susceptible to injury from rough handling during transplanting or from tools; any wound on my roots is an open door for pathogenic infection.
