In vivo production of entomopathogenic nematodes using Galleria mellonella: costs and effect of diets on nematode pathogenicity.

Five separate diets - beeswax (BW), glycerol (Gly), and three types of dog croquettes (DC1, DC2, and DC3) - were used to rear larvae of the greater wax moth, Galleria mellonella. The larvae were later inoculated with five different isolates of entomopathogenic nematodes (EPN) emerging from the insect larvae reared on the five diets. Insect cadavers were then conserved for 1, 2, 3, and 4 wks (T1, T2, T3, and T4, respectively) to evaluate the nematodes' progeny production and to assess the pathogenicity of emerging nematodes to G. mellonella larvae. Larvae fed on DC1 weighed the least (0.18 ± 0.03 g) and those fed on Gly weighed the most (0.22 ± 0.04 g). Gly was effective for insect development but was the most expensive to produce at 6.30 US dollars/kg. No significant difference (P = 0.851) was observed between mortality rates of larvae for nematode isolates for the three best diets (Gly, BW, and DC1) during 1 wk (T1) and 3 wks (T3) after processing at 3 d post-inoculation. All nematode isolates emerged and had the highest population density per insect larva at T1 for isolate Ze4 (Heterorhabditis sonorensis) on BW (553.63 ± 311.97 infective juveniles (IJs)/50 µâ€Šl of suspension, 276,815 IJs/larva) and at T2 on DC1 (488.63 ± 321.37 IJs/50 µâ€Šl, 244,315 IJs/larva) and for isolate Aglali (H. sonorensis) at T1 on Gly (615.18 ± 309.63 IJs/50 µâ€Šl, 307,590 IJs/larva). This study shows the costs and effectiveness of different diets on development and production of G. mellonella larvae and the EPN produced in vivo.Five separate diets ­ beeswax (BW), glycerol (Gly), and three types of dog croquettes (DC1, DC2, and DC3) ­ were used to rear larvae of the greater wax moth, Galleria mellonella. The larvae were later inoculated with five different isolates of entomopathogenic nematodes (EPN) emerging from the insect larvae reared on the five diets. Insect cadavers were then conserved for 1, 2, 3, and 4 wks (T1, T2, T3, and T4, respectively) to evaluate the nematodes' progeny production and to assess the pathogenicity of emerging nematodes to G. mellonella larvae. Larvae fed on DC1 weighed the least (0.18 ± 0.03 g) and those fed on Gly weighed the most (0.22 ± 0.04 g). Gly was effective for insect development but was the most expensive to produce at 6.30 US dollars/kg. No significant difference (P = 0.851) was observed between mortality rates of larvae for nematode isolates for the three best diets (Gly, BW, and DC1) during 1 wk (T1) and 3 wks (T3) after processing at 3 d post-inoculation. All nematode isolates emerged and had the highest population density per insect larva at T1 for isolate Ze4 (Heterorhabditis sonorensis) on BW (553.63 ± 311.97 infective juveniles (IJs)/50 µâ€Šl of suspension, 276,815 IJs/larva) and at T2 on DC1 (488.63 ± 321.37 IJs/50 µâ€Šl, 244,315 IJs/larva) and for isolate Aglali (H. sonorensis) at T1 on Gly (615.18 ± 309.63 IJs/50 µâ€Šl, 307,590 IJs/larva). This study shows the costs and effectiveness of different diets on development and production of G. mellonella larvae and the EPN produced in vivo.

Rice susceptibility to root-knot nematodes is enhanced by the Meloidogyne incognita MSP18 effector gene.

MAIN CONCLUSION: This study revealed novel insights into the function of MSP18 effector during root-knot nematode parasitism in rice roots. MSP18 may modulate host immunity and enhance plant susceptibility to Meloidogyne spp. Rice (Oryza sativa) production is seriously impacted by root-knot nematodes (RKN), including Meloidogyne graminicola, Meloidogyne incognita, and Meloidogyne javanica, in upland and irrigated culture systems. Successful plant infection by RKN is likely achieved by releasing into the host cells some effector proteins to suppress the activation of immune responses. Here, we conducted a series of functional analyses to assess the role of the Meloidogyne-secreted protein (MSP) 18 from M. incognita (Mi-MSP18) during rice infection by RKN. Developmental expression profiles of M. javanica and M. graminicola showed that the MSP18 gene is up-regulated throughout nematode parasitic stages in rice. Reproduction of M. javanica and M. graminicola is enhanced in rice plants overexpressing Mi-MSP18, indicating that the Mi-MSP18 protein facilitates RKN parasitism. Transient expression assays in onion cells suggested that Mi-MSP18 is localized to the cytoplasm of the host cells. In tobacco, Mi-MSP18 suppressed the cell death induced by the INF1 elicitin, suggesting that Mi-MSP18 can interfere with the plant defense pathways. The data obtained in this study highlight Mi-MSP18 as a novel RKN effector able to enhance plant susceptibility and modulate host immunity.

Molecular diversity of Photorhabdus and Xenorhabdus bacteria, symbionts of Heterorhabditis and Steinernema nematodes retrieved from soil in Benin.

The diversity of 43 bacterial strains isolated from Beninese entomopathogenic nematodes was investigated molecularly by analyzing the 16S rRNA, recA, and gyrB genes. Based on 16S rRNA sequence analysis, 15 bacterial strains were identified as Xenorhabdus sp., 27 strains as Photorhabdus sp., and one as Serratia sp. The Xenorhabdus strains were isolated from Steinernema nematodes and identified as Xenorhabdus indica based on 16S rRNA gene and concatenated recA and gyrB sequence analysis. However, analysis of 16S rRNA and concatenated recA and gyrB gene sequences of the Photorhabdus strains, all isolated from Heterorhabditis nematodes, resulted in two separate sub-clusters (A) and (B) within the Photorhabdus luminescens group, distinct from the existing subspecies. They share low sequence similarities with nearest phylogenetic neighbors Photorhabdus luminescens subsp. luminescens HbT, Photorhabdus luminescens subsp. caribbeanensis HG29T, and Photorhabdus luminescens subsp. noenieputensis AM7T.

Differential effect of hot water treatment on whole tubers versus cut setts of yam (Dioscorea spp.).

BACKGROUND: The use of thermotherapy or hot water treatment (HWT) is recommended for the management of plant-parasitic nematodes and other pathogens for a range of planting material, especially vegetatively propagated crops including yams, Dioscorea spp. The sprouting (germination) and consequent viability of yam following HWT, however, appear to be influenced by the post-treatment method of planting (whole or cut setts) and cultivar. The present study was established to evaluate the sensitivity of the most popular yam cultivars in Benin and Nigeria, West Africa, to HWT at 50-53 degrees C for 20 min. RESULTS: Sprouting of both setts and whole tubers of most cultivars was affected by HWT. Across experiments, 47% of HWT material, compared with 61% of non-HWT material, sprouted over 8 weeks. When cut into setts, 41% of HWT or untreated tubers sprouted, compared with 72% of whole tubers. Whole, untreated tubers had highest sprouting rates (84%), and setts following HWT had the lowest (38%). Yam planting material was also not completely free of parasitic nematodes following HWT. The reaction to HWT or cutting was highly cultivar specific. CONCLUSION: Yam cultivars vary in their sensitivity to hot water therapy. Care is therefore advised in selecting yam cultivars for HWT, especially when using cut setts.