Pre-treatment with Dazomet enhances the biocontrol efficacy of purpureocillium lilacinum to Meloidogyne incognita.

BACKGROUND: Meloidogyne incognita greatly restricts the production of protected vegetables in China. Application of biocontrol agent Purpureocillium lilacinum is an important practice to control the nematode; however, instability usually occurs especially in heavily infested field. This study aimed to illustrate the high efficiency of P. lilacinum agent with fumigant Dazomet in vitro. RESULTS: P. lilacinum YES-2-14 showed strong parasitic and nematicidal activities to M. incognita. Pre-treatment with Dazomet significantly enhanced the biocontrol effects of the fungus. After fumigation with Dazomet at a dosage of 7.5 mg kg- 1 soil, parasitism of YES-2-14 on M. incognita eggs increased by more than 50%. Meanwhile, when P. lilacinum fermentation filtrate treated following Dazomet fumigation at 10 and 20 mg kg- 1 soil, the mortalities of second-stage juveniles (J2s) increased by 110.2% and 72.7%, respectively. Both Dazomet and P. lilacinum significantly reduced the penetration ability of J2s to tomato roots. When P. lilacinum filtrate used alone, the J2s penetrating into the young roots decreased by 48.8% at 4 dpi; while in the combined treatment, almost no J2 was detected within the roots at 4 dpi and the number of knots reduced by more than 99% at 45 dpi, indicating a synergistic effect of the biocontrol fungus and fumigant. CONCLUSIONS: Pre-treatment with Dazomet greatly increased the biocontrol efficacy of P. lilacinum to M. incognita. This research provides insight into the efficient management of plant parasitic nematodes and effective use of biocontrol agents.

A novel protein elicitor PeFOC1 from Fusarium oxysporum triggers defense response and systemic resistance in tobacco.

In recent years, it is a hotspot research field on interaction mechanism between elicitor and plant. In this study, a novel hypersensitive response (HR)-inducing protein elicitor was isolated from the culture filtrate of Fusarium oxysporum f. sp. cubense and named PeFOC1, which consisted of 321 amino acids with a molecular weight of approximately 35 kDa. After the inducible expression in Escherichia coli and purification by ÄKTA explore system, the recombinant PeFOC1 also triggered a typical HR in tobacco. In addition, PeFOC1 induced a cascade of defense response in tobacco including production of hydrogen peroxide, deposition of callose, and accumulation of phenolic compounds. Moreover, PeFOC1 significantly improved systemic resistance of tobacco seedlings to tobacco mosaic virus and Pseudomonas syringae pv. tabaci. Real-time quantitative-PCR analysis indicated that several defense-related genes in tobacco, such as NtPR1a, NtNPR1, NtPAL, NtEDS1, NtPDF, and NtLOX, were all up-regulated by the treatment of PeFOC1. All these results collectively demonstrated that PeFOC1 triggered defense response and systemic acquired resistance (SAR) in tobacco. This research not only provides further research on immune mechanism between plant and elicitor, but also sheds new light on strategy for biocontrol in the future.

Secreted protein MoHrip2 is required for full virulence of Magnaporthe oryzae and modulation of rice immunity.

MoHrip2, identified from Magnaporthe oryzae as an elicitor, can activate plant defense responses either in the form of recombinant protein in vitro or ectopic expressed protein in rice. However, its intrinsic function in the infective interaction of M. oryzae-rice is largely unknown. Here, we found that mohrip2 expression was significantly induced at stages of fungal penetration and colonization. Meanwhile, the induced MoHrip2 mainly accumulated in the rice apoplast by outlining the entire invasive hyphae during infection, and its secretion was via the conventional endoplasmic reticulum (ER)-to-Golgi pathway, demonstrating the nature of MoHrip2 as an apoplastic effector. What's more, the disease facilitating function of MoHrip2 was revealed by the significantly compromised virulence of Δmohrip2 mutants on rice seedlings and even on the wounded rice leaves. Inoculations of these mutant strains on rice leaf sheaths showed a reduction in penetration and subsequent expansion of fungal growth, which is probably due to activated host immunity including the expression of certain defense-related genes and the production of certain phytoalexins. Altogether, these results demonstrated the necessity of MoHrip2 in suppression of host immunity and the full virulence of M. oryzae.

The Secreted Protein MoHrip1 Is Necessary for the Virulence of Magnaporthe oryzae.

Secreted effectors from Magnaporthe oryzae play critical roles in the interaction with rice to facilitate fungal infection and disease development. M. oryzae-secreted protein MoHrip1 can improve plant defense as an elicitor in vitro, however, its biological function in fungal infection is not clear. In this study, we found that the expression of mohrip1 was significantly induced in the stages of fungal penetration and colonization. Although dispensable for the growth and conidiation, MoHrip1 was necessary for the full virulence of M. oryzae. Deletion of mohrip1 remarkably compromised fungal virulence on rice seedlings and even on rice leaves with wounds. Rice sheath inoculation assay further demonstrated the defects of mohrip1-deleted mutants on penetration and proliferation in rice cells. Additionally, compared with WT and complementation strain, the inoculation of mohrip1-deleted mutants induced a higher expression of specific defense related genes and a higher production of specific defensive compounds in rice leaves. These data collectively indicated that MoHrip1 is necessary for fungal penetration and invasive expansion, and further full virulence of rice blast fungus.