Screening Of Actinomyces Strains Producing Secondary Metaboletes With Nematicidal Activity

Culture filtrates of 344 actinomyces strains isolated from 30 soil samples were tested of knock-down efficiency in vitro against J2 of root-knot nematodes. Seventeen strains among them, coded as LH004, LH010, LH018, LH053, LH054, LH082, LH117, LH120, LH121, LH132, LH139, SH037, NJ001, NJ024, NJ026, NJ051 and NJ095 respectively, showed strong nematicidal activity .All of their 8-fold diluted culture filtrates had more than 85% knock-down efficiency.Then the 17strains' culture filtrates were further assayed control effect on root-knot nematodes.3 strains, which were NJ026, LH117 and LH121 respectively, could inhibit gall and egg mass formation most significantly, 2ml culture filtrates reduced 62.3%, 85.1%, 67.0% gall formation and 63.6%, 82.7%, 68.2 % egg mass formation. Then successive 6 generations of the 3 strains were examined genetic stability producing active nematicidal substance, results showed that NJ026 lost its active substance producing ability within 6 generations, LH117 remained nematicidal activity after 6 generations but the decreasing trend may be discerned, only LH121 always demonstrated stable strong nematicidal activity. Based on the above experiment, LH117 and LH121 were considered as potential to be used in practice for root-knot nematodes control. Besides nematicidal activity, culture filtrates of LH117 and LH121 both could inhibit growth of five important vegetable pathogenic fungi, namely Colletotrichum gloeosporioide,Gloeosporium piperatwn, Alternaria solani, Cladosporium cucumerinum and Colletotrichum orbiculare.Action mode of the two strains against root-knot nematodes was probed. Culture filtrates of LH121 could completely knock-down all the J2 tested within 4h, but most recovered their movements in fresh water; 12h later, no recovery was observed; 24h later, all of the individuals turned transparent observed under dissect microscope, which revealed that electrolyte leakage occurred. LH117 knocked down 90% of J2 within 8h but most recovered movements in fresh water, 24h later 26.3% of J2 could still recover. Both strains affected egg hatching. 72h treatment with LH121 no egg hatched any longer and the egg mass turned to red-brown; 72h treatment with LH117 the inhibition ratio was 82.3% compared with CK. Experiments in vivo revealed that both strains control root-knotnematode mainly through killing J2 or affecting their activity, they cannot influence nematode development after the nematode-plant endoparasite relationship has been established.In order to promote active substance production, fermentation condition of the two actinomyces strains was optimized. Results was that the optimum fermentation condition of the two strains were almost the same. The culture filtrates which utilized No.l nutrition components, with initial PH7-8, shaking 4-5 days at ITOrpm, 6 days strains age around showed the strongest nematicidal activity. Both strains utilized complex carbon sources such as soluble starch and oatments better than simple carbon sources, and complex organic nitric sources such as beef extract and peptone better than inorganic nitric sources.LH117 and LH121 were identified as Streptomyces cuspidosporus and Streptomyces reseofulvus respectively based on their morphological and physiological properties according to the methods recommended by International Streptomyces Project (ISP).