Abstract:

【Objective】 Chitinases produced by egg-parasitic fungus Pochonia chlamydosporia have been suggested to play an important role in digestion of root knot and cyst nematode eggshells. The egg-parasitic fungi with chitinase activity is one of the most important biochemical characters in suppression of egg hatching, and can be used for evaluation of the biocontrol potential of those fungi. 【Method】 The chitinolytic systems and exochitinase produced by 7 isolates of P. chlamydosporia were measured by means of NAG(N-acetyglucosamine) and pNP(ρ-nitrophenol) respectively. 【Result】 The results showed that all the isolates hade different levels of exochitinase activity, however only the isolates QNAV97-2, NRRL13094, CFCC84964 and CFCC80919 had activity of chitinolytic systems. On SDS-PAGE analysis with 0.01% glycol chitin, two and four protein bands with chitinase activity were detected, the chitinases of 38.9kDa and 39.8kDa produced by CFCC80964 and QNAV97-2 were believed to be the CHI43 purified in early studies. Inhibitory rates to egg hatching of Meloidogyne incognita by 4 isolates with chitinolytic activity were ranged from 40.32% to 55.15%, however, those by 3 isolates without chitinolytic activity were lower than 20%. Microscopy observations demonstrated that the eggshells of M. incognita was deformed and destroyed in the treatment of culture filtrates from P. chlamydosporia. 【Conclusion】 It is concluded that the chitinases produced by P. chlamydosporia causes lysis of the eggshell of M. incognita, especially immature eggs at early embryonic development stage, and result in egg hatching inhibition and/or egg kill. The digestion of the eggshell by chitinase activity plays an important role in the control of M. incognita. Difference in chitinase activity levels produced by P. chlamydosporia may result in their difference in nematicidal activity to nematodes.

Key words: Pochonia chlamydosporia, Meloidogyne incognita, chitinases, egg-hatching