Disease Progression by Active Mycelial Growth and Biocontrol of Pythium ultimum var. ultimum Studied Using a Rhizobox System

Abstract

This study demonstrates that outward growth of mycelium from primary foci through bulk potting mix to roots of adjoining plants can be an important means of spread of damping-off and root rot caused by Pythium ultimum. The use of a rhizobox system, which confines plant roots, enabled us to study the spread of actively growing mycelium between root systems placed at precise distances from each other. In steamed potting mix, hyphae of P. ultimum on average grew 9.6 cm from diseased root tissue compared to 5.3 cm in raw potting mix. The density of mycelium was highest within the first 2 cm from the infected root tissue, decreasing with increasing distances from the roots. Accordingly, the disease on adjacent plants decreased as the distance from infected roots increased. The time required for damping-off of adjacent plants was 3 days slower in raw as compared to steamed potting mix and increased by 2 days for each additional centimeter between the rhizoboxes. The presence of Trichoderma harzianum diminished the production of secondary inoculum and reduced the ability of P. ultimum hyphae to extend through bulk potting mix. In conclusion, the concentration of the primary inoculum, the plant density, the distance separating diseased from healthy roots, the resident microflora, and the presence of an antagonist were shown to be important factors affecting disease spread by mycelial growth.

Pathogenic and molecular characterization of Pythium species inducing root rot symptoms of common bean in Rwanda

“…were the most frequently isolated fungi and the widespread in Rwanda. Contrary to our findings, in a similar investigation performed by Green and Dan (2000), it was found that Pythium ultimum was the most widespread Pythium species that attacks a large number of plant species in Denmark (Mukalazi, 2004).…”

Lateral roots of carrot have a low impact on alloinfections in cavity spot epidemic caused by Pythium violae

“…Our results showed that P. violae can spread more than 90 mm throughout a sterilized sandy soil after 5 weeks. This distance is compatible with previous results obtained by using taproot transplantation as a method of soil infestation by P. violae and with results obtained by Green and Jensen (2000) for P. ultimum var. ultimum (in steamed potting mix, hyphae on average grew 96 mm from diseased root tissue).…”

“…Following Green and Jensen (2000) and Rekah et al (1999), using Petri dishes and a water agar medium, we verified that a 200-lm nylon mesh does not prevent the spread of mycelium of P. violae. Then, rectangular rhizoboxes were divided into two identical compartments (the donor and the receptor compartments) using that nylon mesh, which created a 30-mm wide central buffer zone designed to prevent contact between the carrot root systems without preventing movement of Pythium through the nylon mesh (Fig.…”

“…Consequently, the experiment established that active mycelial growth from CCS lesions is probably the most prevalent mechanism involved in alloinfections by P. violae because zoospores are of little importance (Van der Plaats-Niterink 1981). Similarly, Green and Jensen (2000) showed in controlled conditions that growth of mycelium from primary foci within the potting mix to roots of adjoining plants can be an important means of the spread of cucumber damping-off and root rot caused by P. ultimum var. ultimum.…”

“…radicis-lycopersici causing fusarium crown and root rot of tomato (Rekah et al 1999), and Pythium irregulare (Burdon and Chilvers 1975) and P. ultimum var. ultimum (Green and Jensen 2000) causing cress and cucumber damping off, respectively.…”