Reactive oxygen species, cell death, callose deposition and photosynthesis of tomato after infection with Meloidogyne incognita may contribute to aggravated Fusarium wilt

Although it has been shown that nematode infection aggravates Fusarium wilt in tomato, the mechanisms underlying this phenomenon are still unknown. We analysed morphology, biochemistry and molecular biology of tomato plants infected with Meloidogyne incognita or Fusarium oxysporum f. sp. lycopersici (Fol) alone or in combination. We verified that M. incognita infection facilitated the invasion of Fol. M. incognita infection promoted the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) in tomato inoculated with Fol. The expression of two ROS producing genes: Solyc07g039310.1 (PAO5) and Solyc05g053100.3 (LPD1) and four ROS scavenger genes: Solyc01g067860.3 (PER24), Solyc02g079500.4 (TAP1), Solyc04g071900.4 (PER12) and Solyc10g078890.2 (POD), was upregulated to a greater extent in tomato after infection with M. incognita in combination with Fol compared with Fol alone. Cell death in tomato roots infected with both pathogens was more pronounced than in response to Fol alone. Callose spots in tomato roots inoculated with both pathogens were fewer than in those inoculated with Fol alone. Further transcriptome profiling and KEGG enrichment analyses revealed that a photosynthesis-antenna protein pathway in tomato was enriched after M. incognita infection with or without Fol. Twenty-four out of the 30 genes in this pathway were upregulated due to M. incognita infection. We further used qRT-PCR to confirm the expression of six of these genes. The results suggest that increased accumulation of ROS and MDA, increased cell death, reduced callose accumulation and increased photosynthesis caused by M. incognita may help aggravating Fusarium wilt.