Induction of resistance in potato tuber tissue to control Fusarium sambucinum.

摘要

Fusarium sambucinum is one of the causal agents of Fusarium dry rot in potato tubers. Although thiabendazole has been the primary control of Fusarium dry rot, development of resistance to this fungicide has required that new control strategies be developed. Induced resistance may be one new approach to controlling dry rot.; Potato tuber tissue was treated with several materials known to induce resistance in other plants. These included: salicylic acid, salicylic acid analogues, non-protein amino acids, chitosan, fatty acids and homogenate of Phytophthora infestans mycelium. Only treatments of potato tuber tissue with chitosan and homogenate of Phytophthora infestans mycelium (MH) reduced infection by F. sambucinum. However, the tuber tissue response was visually different between the MH and chitosan treatments and chitosan was slightly more effective at reducing infection.; Protein analysis revealed both chitosan and MH induced a number of putative plant defense mechanisms. The pathogenesis-related protein chitinase was locally and systemically induced in tubers in response to both treatments. β-1,3-glucanase was locally induced by both treatments and systemically induced in response to MH. Treatment with MH elicited a greater increase in chitinase and β-1,3-glucanase activity than treatment with chitosan. Local induction of the oxidative enzymes peroxidase and polyphenol oxidase (PPO) was also observed in response to both treatments. Steroid glycoalkaloid accumulation, which has been shown to inhibit F. sambucinum growth and spore germination, was suppressed by both chitosan and MH treatments.; Cytological examination of chitosan-treated tissues with autofluorescence and histochemical staining revealed accumulation of non-soluble phenolic compounds in the cell wall areas of tuber tissue, suggesting cell wall modifications had occurred in response to chitosan treatment. Additionally, lacmoid staining revealed that chitosan treated tissue developed a barrier of callose two to three layers from the treated surface.; Induction of resistance by chitosan and P. infestans mycelium homogenate is probably a result of multiple plant defense mechanisms (pathogenesis-related proteins, oxidative enzymes, accumulation of phenols, cell wall changes and callose deposition) working simultaneously to stop the ingression of F. sambucinum. Induced resistance is therefore a promising alternative to fungicides for the control of Fusarium dry rot and because it controls F. sambucinum using multiple defense mechanisms it may be a more stable form of resistance than fungicides.