Use of cellophane to study the infection structures of PNG cocoa isolates of Phytophthora palmivora in vitro
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RESEARCH NOTE
Use of cellophane to study the infection structures of PNG cocoa isolates of Phytophthora palmivora in vitro Francine Perrine-Walker 1,2 Received: 1 September 2020 / Accepted: 24 September 2020 / Published online: 29 September 2020 # Australasian Plant Pathology Society Inc. 2020
Abstract Cocoa pod isolates of Phytophthora palmivora (Ppal) from different locations in Papua New Guinea (PNG) were grown in the presence of cellophane to determine their abilities to mechanically penetrate this barrier and to gain access to the growth media below. Four Ppal isolates, MAG14, MAG30, MAG50, NSP11 and the plant root pathogenic oomycete P. cinnamomi for comparison, were tested for their cellophane penetrating ability. All were able to penetrate the cellophane by forming appressoria and infection peg-like structures. All Ppal isolates formed frond-like structures which grew at various depths within the cellophane while P. cinnamomi formed hyphal aggregations and frond-like structures within the cellophane. This is the first in vitro study demonstrating how Ppal can modify its hyphal morphology to form lobed structures upon contact to the cellophane surface and branched aggregating hyphae within cellophane to gain access to growth media below. Keywords Infection . Cellulose . Oomycete . Plant pathogen . Penetration assay
The plant pathogenic oomycete, Phytophthora palmivora (Ppal) causes rot diseases in many plants including cocoa (Theobroma cacao L.) (Acebo-Guerrero et al. 2012; Erwin and Ribeiro 1996). It infects various parts of the cocoa plant and when found in the cocoa pod causes black pod rot (Guest 2007). The latter has economic impact as the infected pods can no longer be sold contributing to the economic loss to many cocoa farmers around the world including those in Papua New Guinea (PNG) (Guest 2007). The oomycete’s infection process begins when motile zoopores, released from cadacous sporangia, adhere to the plant surface, and form cysts which germinate after being triggered by environmental factors. The germ tubes enter plant tissue directly via openings such as stomata or via wounding and by the formation of an appressorium upon contact on the plant wall cell surface or the plant Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13313-020-00750-4) contains supplementary material, which is available to authorized users. * Francine Perrine-Walker [email protected] 1
School of Life and Environmental Sciences, University of Sydney, LEES Building (F22), Camperdown, NSW 2006, Australia
2
The University of Sydney Institute of Agriculture, 1 Central Avenue, Australian Technology Park, Eveleigh, NSW 2015, Australia
cuticle. An appressorium peg allows the oomycete to penetrate the plant cell wall and Ppal invaginates into the plant cell to form an haustorium during its biotrophic growth stage and switches to a necrotrophic lifestyle where plant disease symptoms can be observed. Work by Saul Maora et al. (2017) collected 263 isolates of Ppal fro
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