A novel screening strategy to identify biocontrol fungi using protease production or chitinase activity against Meloidogyne root-knot nematodes

Abstract

We isolated 137 fungal strains from females and eggs of Meloidogyne spp. collected from plant roots and infested soil in Jiangsu, China, and examined their in vitro protease production and chitinase activities. We then selected 20 strains, each with a protease production higher than 2 (protease production was measured as the ratio of diameters of the zone of clearing to that of the colony) and a chitinase activity higher than 0.2 U/min mL. For these strains, we examined their egg parasitic rates, mortality rates of stage 2 juvenile (J2), egg hatching rates and evaluated their biocontrol efficacies under greenhouse conditions. The biocontrol efficacies of these 20 potential biocontrol fungal strains ranged from 29 to 58%. The actual biocontrol efficacy against Meloidogyne root-knot was highly correlated with the in vitro protease production (r=0.82), chitinase activity (r=0.80), and mortality of J2 (r=0.76), but poorly correlated with the egg parasitic rate (r=0.51) and the egg hatch rate (r=0.52). Based on these results, we suggest that in vitro protease production or chitinase activities of the fungal strains could be an applicable indicator for assessing biocontrol efficacy against nematodes. This notion was also supported by our field experiments on tomatoes with Paecilomyces lilacinus strains XT18, XCS46 and Pochonia chlamydosporia strain XT124, which reached the biocontrol efficacies of 60.7, 51.5 and 48.1% in 2007; and 67.8, 57.3 and 53.2% in 2008, respectively.

Keywords:

• Meloidogyne incognita
• fungi
• protease production
• chitinase activity
• biocontrol efficacy

Acknowledgements

The pure culture of Meloidogyne incognita was provided by Prof. Jian-Hua Xu (1964–2006), Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, China. This study was supported by a grant-in-aid for science research from the 863 high technology Program of China (2006AA10A211), grants from Governmental Scientific Ministrant Project of Beijing Agricultural Council (BJNY2007-03-02) and program for New Century Excellent Talents in University (NCET-06-0492).

Additional information

Notes on contributors

Li-Hui Wei

Contributed equally to this study and are regarded as joint first authors