Tissue-Specific Localization of Pea Root Infection by Nectria haematococca. Mechanisms and Consequences

Abstract

Root infection in susceptible host species is initiated predominantly in the zone of elongation, whereas the remainder of the root is resistant. Nectria haematococca infection of pea (Pisum sativum) was used as a model to explore possible mechanisms influencing the localization of root infection. The failure to infect the root tip was not due to a failure to induce spore germination at this site, suppression of pathogenicity genes in the fungus, or increased expression of plant defense genes. Instead, exudates from the root tip induce rapid spore germination by a pathway that is independent of nutrient-induced germination. Subsequently, a factor produced during fungal infection and death of border cells at the root apex appears to selectively suppress fungal growth and prevent sporulation. Host-specific mantle formation in response to border cells appears to represent a previously unrecognized form of host-parasite relationship common to diverse species. The dynamics of signal exchange leading to mantle development may play a key role in fostering plant health, by protecting root meristems from pathogenic invasion.

The Organization Pattern of Root Border-Like Cells of Arabidopsis Is Dependent on Cell Wall Homogalacturonan

“…Maintaining border-like cells close to the root cap either in the wild type (file of attached cells) or in the qua1-1 mutant (isolated cells entrapped in mucilage) might be important for the function of border-like cells, possibly in protecting the root tip. While a protective function of the root cap has been demonstrated for border cells (Hawes et al, 2000;Gunawardena et al, 2005), the potential function of border-like cells in relation to root health has not been assessed.…”

Alarming occurrence of Fusarium wilt disease in pea (Pisum sativum L.) cultivations of Jabalpur district in Central India revealed by an array of pathogenicity tests

“…These exudates contain soluble (mainly sugars and amino acids) and volatile chemicals released from germinating seeds and actively growing roots which act as stimuli for infection process (Nelson, 1991). Gunawardena (2005) stated that flavonoids and isoflavonoids commonly present in the exudates of legumes may also be responsible for instigating Fusarium infection. Stasz et al (1980) Pathogenic forms of F. oxysporum are reported to penetrate a host root either through wounds or directly through root apices (Nelson, 1981).…”

“…The plates were incubated at 25 o C for seven days and observed after every 24 hours. Infection of F. oxysporum on pea seeds of the selected varieties was studied and evaluated on a 30 point scale (modification of method by Ondrej et al, 2008;Gunawardena, 2005). If a germinated seed showed coat infection as well as radical tip infection then two points or if either was true then one point was given.…”

Deciphering the Responses of Root Border-Like Cells of Arabidopsis and Flax to Pathogen-Derived Elicitors

“…Root border cells impact plant health and survival by protecting the root meristem from pathogenic infection, as has been clearly demonstrated for pea (Pisum sativum) against the fungus Nectria haematococca (Gunawardena and Hawes, 2002;Gunawardena et al, 2005). Border cells have also been shown to repel pathogenic bacteria by means of their secreted mucilage (Hawes et al, 2000).…”