Histopathology of infection of bean with Pythium myriotylum compared with infection with other Pythium species

Abstract

Clusters of abundant appressoria formed from branching hyphae of mycelial inoculum of Pythium myriotylum on the surface of bean hypocotyls and roots. Pythium aphanidermatum usually produced single appressoria, but sometimes small clusters of appressoria. Pythium ultimum produced only single appressoria. Early pathogenesis of all species was characterized by rapid radial growth of hyphae in the epidermal cells, which was more rapid than in the cortex. These hyphae were constricted at the host cell walls. Invaded tissue and adjacent cells stained differently from healthy cells with all isolates. Aerial hyphae were produced from vesicles below the cuticle or within epidermal cells soon after infection was established. Safranin-staining materials were observed in the xylem, phloem, and tannin sacs. Zoospores of P. myriotylum and P. aphanidermatum germinated and produced long prepenetration hyphae, which branched and formed single appressoria. Oospores of P. myriotylum, P. aphanidermatum, and P. ultimum, after germination, produced branched hyphae and single appressoria. Penetration, rapid advance through epidermal cells, and ramification of cortical and vascular tissue were identical with those of mycelial inoculum. Sporangia of all three species formed intercellularly and intracellulary within 48 h and predominantly in the epidermis and upper cortex. Oogonia were produced intercellularly and intracellularly in 4 day s throughout the tissue, but mainly in the inner two thirds of the cortex. Sporangia of P. myriotylum and P. aphanidermatum in infected bean hypocotyls germinated within 3 h when flooded with tap water and produced zoospores within 6 h. When similar tissue was air-dried for 3 days or rapidly dried for 3 h. there was neither germination nor zoospore production.

Production of Zoospores, Mode of Infection, and Inoculum Potential of Pythium myriotylum Propagules on Cocoyam

“…However, in the case of the mycelium, inoculation followed production of an infection peg. In both situations, penetration and invasion of the roots by P. myriotyium propagules was inter-and intracellular, A similar report made on the histopathology of P, myriotyium in cotton, tomato, eggplant, and bean seedlings, indicated that the hyphae moved both intercellularly and intracellularly through the cortex during advanced pathogenesis (Dow and LUMSDEN 1975).…”

“…This is the first report that detached mycelia of P. myriotyium can be induced to produce zoospores in vitro, DRECHSLER (1943) reported that zoospores were produced on undetached mycelia of P. myriotyium on maize-meal or lima bean agar medium in Petri dishes and flooded with tap water. Dow and LUMSDEN (1975) also reported that P. myriotyium zoospores were produced on infected bean hypocotyls or roots by washing the P. myriotyium culture and soaking them in tap water. The size and shape, as well as the length, of the fiagelia of zoospores of P. myriotyium were similar to earlier reports (DRECHSLER 1943, Dow andLUMSDEN 1975).…”

“…Dow and LUMSDEN (1975) also reported that P. myriotyium zoospores were produced on infected bean hypocotyls or roots by washing the P. myriotyium culture and soaking them in tap water. The size and shape, as well as the length, of the fiagelia of zoospores of P. myriotyium were similar to earlier reports (DRECHSLER 1943, Dow andLUMSDEN 1975).…”

“…The use of zoospore(s) as inoculum, or for the maintenance of P. myriotyium isolates in pure culture as an alternative to myceiial tip tranfer when the isolate has been contaminated with other pathogens, requires that the zoospores be produced consistently from sporangia and in adequate numbers. Dow and LUMSDEN (1975) were able to produce zoospores of P. myriotyium within 6 h infected bean hypocotyls or roots after flooding with tap water. PACUMBABA et al (1991a) in their preliminary study of the pathogen, reported that zoospores of P. myriotyium could be produced on artificial medium.…”

New Report of Pythium Soft Root Rot in Mulberry and its Cultural and physiological Studies

“…The highest Pythium sp. dry mycelial weight was recorded at the pH of 7.0 (386.60 mg) which is on par with the pH 6.5 (352.20 mg) and these are followed by pH 7.5 (234.50 mg), pH 6.00 (201.30 mg), pH 5.5 (191.18 mg), pH 5.0 (191.00 mg), 4.5 (155.80 mg), 8.0 (135.70 mg), 8.5 (45.00 mg) and no growth was seen at 3.5 pH, 4.0 pH and 9.5 pH Dow and Lumsden (1975) and which were white to colourless reported by Alhussaen (2019). Pathogenicity was proved by inoculating mycelial plugs of fungus Pythium sp.on wounded root of healthy mulberry plant.…”