For everyone else that cares about the studies of root rot in hydroponics and the results. Here is some info.
An understanding of root rot epidemics is fundamental to the development and refinement of methods and practices to manage the disease in hydroponic crops, but remains fragmentary. While root rot is almost universal in commercial hydroponic systems, and in many instances becomes sufficiently severe to cause serious crop losses, it is also true that in many other instances progress and spread of the disease is comparatively slow and losses are perceived as minor. From the literature, and an abundance of anecdotal evidence from greenhouse growers and crop advisory personnel, it is clear that a myriad of variables significantly influence
Pythiumspecies and root rot development in hydroponic systems. Important variables range from subtleties such as calcium in the root zone, which at millimolar levels strongly influence adhesion of zoospores to roots (33), to elevated temperature, which can bring about abrupt and explosive increases in root necrosis in large portions of crops (4, 28, 39, 54, 61, 83, 107). This portion of the present article will now focus on effects of factors associated with the host, the pathogen, the environment of the nutrient solution and plant canopy, and human interferences on disease severity and pathogen ecology. Excellent perspectives of the general principles of epidemiology are given in Zadoks & Schein (119) and Bergamin Filho & Amorim (7). For a critical review of the epidemiology of diseases caused by
Pythium spp. in plants grown in soil, attention is drawn to Martin & Loper (61).
Recent studies in our laboratory have demonstrated for the first time that environmental stress factors can increase the susceptibility of hydroponically-grown plants to
Pythium root rot. The studies were conducted using pepper plants in single-plant hydroponic units with aerated nutrient solution. When temperature of the nutrient solution was raised to 28ºC or 34ºC for a few hours or days and subsequently lowered to 22-24ºC
prior to inoculation of the root systems with
P. aphanidermatum, root browning progressed earlier and more rapidly than in control plants maintained at 22-24ºC before inoculation (C.R. Sopher & J.C. Sutton, unpublished). Similarly, when plants were kept in nutrient solution (pH 5.
amended with certain simple phenolic compounds for 48 h and then placed in unamended solution for 24 h before inoculation with
P. aphanidermatum, disease severity increased more rapidly than in untreated controls (103). This finding suggested that phenolics escaping from diseased roots might predispose downstream healthy plants to attack by
Pythium. Collectively, the studies demonstrated that high temperature and phenolic compounds predisposed the plants to root rot. By definition, predisposition refers to increased susceptibility of plants to disease brought about by environmental factors acting
prior to infection by the pathogen (39). It is likely that other environmental stressors or stress conditions, such as low intensity light and low concentration of dissolved oxygen in the nutrient solution also predispose plants to
Pythium root rot. Chérif
et al. (14) found that
Pythium F colonized roots of hydroponically-grown tomatoes more extensively when concentration of dissolved oxygen was moderate (5.8-7.0%) or low (0.8-1.5%), than at high levels (11-14%), however, it was not determined whether the influence of reduced oxygen was through increasing susceptibility of the host, or through effects on the pathogen or the host-pathogen interaction.
The info is abundant out there. You just have to know how to read and have the drive to want to know why and how things operate.
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