Annemie Elsen

Relative mycorrhizal dependency and mycorrhiza-nematode interaction in banana cultivars (Musa spp.) differing in nematode susceptibility

Four Musa cultivars, differing in nematode susceptibility, were selected to study their relative mycorrhizal dependency and to study the interaction between the arbuscular mycorrhizal fungus (AMF), Glomus mosseae, and two migratory endoparasitic nematodes, Radopholus similis and Pratylenchus coffeae. Mycorrhization with G. mosseae resulted in significantly better plant growth, even in the presence of R. similis and P. coffeae. No differences in relative mycorrhizal dependency (RMD) were observed among the four cultivars. G. mosseae suppressed nematode population build-up in Grande Naine and Pisang Jari Buaya. Only in the case of R. similis (Indonesian population) in Pisang Jari Buaya, no significant suppression was observed. In the case of P. coffeae, the AMF reduced the damage in the roots, caused by the nematodes. For R. similis, no reduction of damage was observed. In all, except one experiment, the frequency of the mycorrhizal colonisation was negatively affected by the nematodes.

Arbuscular mycorrhizal fungi reduce root-knot nematode penetration through altered root exudation of their host

AimsArbuscular mycorrhizal fungi (AMF) can control root-knot nematode infection, but the mode of action is still unknown. We investigated the effects of AMF and mycorrhizal root exudates on the initial steps of Meloidogyne incognita infection, namely movement towards and penetration of tomato roots.MethodsM. incognita soil migration and root penetration were evaluated in a twin-chamber set-up consisting of a control and mycorrhizal (Glomus mosseae) plant compartment (Solanum lycopersicum cv. Marmande) connected by a bridge. Penetration into control and mycorrhizal roots was also assessed when non-mycorrhizal or mycorrhizal root exudates were applied and nematode motility in the presence of the root exudates was tested in vitro.ResultsM. incognita penetration was significantly reduced in mycorrhizal roots compared to control roots. In the twin-chamber set-up, equal numbers of nematodes moved to both compartments, but the majority accumulated in the soil of the mycorrhizal plant compartment, while for the control plants the majority penetrated the roots. Application of mycorrhizal root exudates further reduced nematode penetration in mycorrhizal plants and temporarily paralyzed nematodes, compared with application of water or non-mycorrhizal root exudates.ConclusionsNematode penetration was reduced in mycorrhizal tomato roots and mycorrhizal root exudates probably contributed at least partially by affecting nematode motility.

Use of Root Organ Cultures To Investigate the Interaction between Glomus intraradices and Pratylenchus coffeae

ABSTRACT The interaction between Glomus intraradices and Pratylenchus coffeae on transformed carrot roots was studied in root organ culture. G. intraradices provided the roots with increased protection against P. coffeae by suppressing nematode reproduction in the roots. The internal and external mycorrhizal development was not influenced by the presence of the nematodes.

Recolonisation by nematodes of hot water treated cooking banana planting material in Uganda

In East Africa, the cooking bananas (Musa spp., AAA group, subgroup Matoke) are the major food crop. Yields are decreasing due to increasing damage caused by a complex of pests and diseases, including plant-parasitic nematodes. Planting of infected material is the principle means of dispersal for these nematodes. An option to control the nematodes in planting material is hot water treatment but the benefits depend on the rate of recolonisation. Therefore, on-farm trials were carried out at five localities representing Musa production systems in Uganda. Hot water treatment of planting material slowed down build-up of Radpholus similis at least until 30 months after planting. This was not only the case for the treated mother plants but also for the suckers that developed from these mother plants. A similar trend was observed for Helicotylenchus multicinctus. Hot water treatment also slowed down the build-up of Pratylenchus goodeyi but this effect was less pronounced.

Phenols and lignin are involved in the defence response of banana (Musa) plants to Radopholus similis infection

The role of lignin and phenols in plant defence ranges from preformed characteristic to inducible physical and chemical response against nematode infection. Our study shows the involvement of lignin and phenols in the defence of two newly identified resistant banana (Musa) genotypes to burrowing nematode Radopholus similis infection. Results were compared with reference resistant and susceptible banana cultivars. Histochemical analysis of root cross sections showed a more extensive secondary cell wall lignification of vascular bundles in R. similis-infected plants than in the nematode non-infected plants. Increased extensive lignification was not associated with the cortex cells that are directly attacked by the nematode. This showed that the increased lignification is a general defence response to protect the vascular bundle from damage rather than resisting the nematode development and reproduction at the root cortex. Histochemical localisation showed no preformed phenolic cells in the cortex of the non-infected, R. similis-resistant and -susceptible Musa genotypes. By contrast, phenolic substances were the major constituents of the nematode-infected necrotic cells. Phenols and lignin contents were also quantitatively assayed. The Folin-Ciocalteu assay confirmed the increase in phenol content of nematode-infected root cells. Phenol content in nematode-infected plants was twice the amount of phenol content in nematode non-infected plants at 3 weeks after infection. This is possibly due to the biosynthesis or accumulation of secondary metabolites such as phenolic phytoalexins in the nematode infection sites of all the banana genotypes. This study clearly demonstrates that phenols and lignin play an important role in the defence mechanisms of Musa to R. similis infection.

Effect of temperature on the in vitro reproductive fitness of Pratylenchus coffeae populations from Vietnam

The in vitro reproductive fitness on carrot discs of 10 Pratylenchus coffeae populations collected from different agricultural crops in different agro-ecological regions in Vietnam was studied and compared with the reproductive fitness of a P. coffeae population from Ghana. Few major differences in in vitro reproductive fitness on carrot discs among the 10 P. coffeae populations from Vietnam examined (with the exception of one population originally isolated from the roots of an unidentified ornamental tree and one population originally isolated from banana), and between these populations and the P. coffeae population originally isolated from banana in Ghana were observed. Our observations indicate that although the optimum temperature for reproduction of three P. coffeae populations from Vietnam examined is 25 °C to, at least, 30 °C, these populations are also tolerant to low temperatures (15–20 °C) enabling them to survive the low temperatures which occur during the winter in the northern and central parts of Vietnam.

Effect of plant lectins on the host-finding behaviour of Radopholus similis

Summary ‐ The motility and the chemotactic response towards plant roots of Radopholus similis , after treatment with novel types of lectins, were examined in vitroby analysing movement tracks on agar plates. Six plant lectins belonging to e ve different lectin families and a banana thaumatin-like protein (BanTLP) were included in the experiment. A 1% concentration of Phaseolus vulgaris agglutinin (PHA) had an adverse effect on the motility of R. similisfemales: 63% showed no or very little movement on agar plates compared to an average of 33% for other lectins and 3% for the control treatment. A 0.05% concentration of PHA still reduced the motility of R. similis females by 75%. Concanavalin A and wheat germ agglutinin did not alter the chemotactic response towards plant roots, despite binding of both lectins to R. similis. In contrast, Galanthus nivalis agglutinin (GNA) reduced orientated movement of R. similis towards plant roots. Subsequently, secretions of R. similis were stained with Coomassie Brilliant Blue R. Nematodes treated with GNA produced secretions less abundantly compared to the control treatment and BanTLP. The other lectins in the experiment had variable effects on secretion.