Histological Characterization of Resistance to Different Root-Knot Nematode Species Related to Phenolics Accumulation inCapsicum annuum

Abstract

In the pepper Capsicum annuum CM334, which is used by breeders as a source of resistance to Phytophthora spp. and potyviruses, a resistance gene entirely suppresses reproduction of the root-knot nematode (Meloidogyne spp.). The current study compared the histological responses of this resistant line and a susceptible cultivar to infection with the three most damaging root-knot nematodes: M. arenaria, M. incognita, or M. javanica. Resistance of CM334 to root-knot nematodes was associated with unidentified factors that limited nematode penetration and with post-penetration biochemical responses, including the hypersensitive response, which apparently blocked nematode migration and thereby prevented juvenile development and reproduction. High-performance liquid chromatography analysis suggested that phenolic compounds, especially chlorogenic acid, may be involved in CM334 resistance. The response to infection in the resistant line varied with root-knot nematode species and was correlated with nematode behavior and pathogenicity in the susceptible cultivar: nematode species that quickly reached the vascular cylinder and initiated feeding sites in the susceptible cultivar were quickly recognized in CM334 and stopped in the epidermis or cortex. After comparing our data with those from other resistant pepper lines, we suggest that timing of the resistance response and the mechanism of resistance vary with plant genotype, resistance gene, and root-knot nematode species.

Post‐infection development and histopathology of Meloidogyne arenaria race 1 on Arachis spp.

“…The post-penetration response of the incompatible A. stenosperma roots was considered a classical HR, which occurred after 8-19 DAI. This is in line with several reports on other plants in which HR was correlated with resistance to nematodes (Dropkin, 1969;Bleve-Zacheo et al, 1998;Rodrigues et al, 2000;Anthony et al, 2005;Pegard et al, 2005). However, the differentiation time of HR differs between plants, occurring hours after penetration for some, and only after days for others.…”

“…Failure of J2s to penetrate the resistant A. stenosperma may indicate physical or chemical root barriers. Such barriers were suggested previously for resistant grape rootstock (Anwar & McKenry, 2002), cotton (Anwar et al, 1994), soyabean (Dropkin & Nelson, 1960), pepper (Pegard et al, 2005) and coffee cultivars (Anthony et al, 2005). It may also indicate that the root exudates did not attract or perhaps even repelled the J2s, or that the J2s penetrated and then left the roots.…”

Development of virulence to Meloidogyne incognita on resistant pepper rootstocks

“…incognita has a great capacity to respond to environmental selection, even overcoming the known ge- netic resistance of some hosts (Castagnone-Sereno, 2006). The resistance response of pepper to M. incognita is expressed as cell necrosis and pitted tissues once juveniles have established in the roots, or as the partial or total inhibition of their multiplication once installed (Bleve-Zacheo et al, 1998;Pegard et al, 2005;Castagnone-Sereno, 2006). The selection of populations that overcome resistance under natural conditions is favoured by the repeated monoculture of cultivars carrying resistance genes.…”

Gene expression analysis inMusa acuminataduring compatible interactions withMeloidogyne incognita

“…Root segments were also embedded in resin for sectioning (4 lm). Root fragments were excised, fixed, and embedded in Technovit 7100 epoxy resin (Kulzer Friedrichsdorf), as described by Pegard et al (2005). Sections were subsequently stained (1 min at 60 C) with 0Á05 % toluidine blue in 0Á1 M sodium phosphate buffer, pH 5Á5 and observed under bright-field light microscopy (Zeiss Axiophoto).…”