JIA-2019-11

2568 LIU Ying et al. Journal of Integrative Agriculture 2019, 18(11): 2561–2570 present research demonstrated that the A . welwitschiae isolate significantly repelled the penetration of nematodes. However, the ability of a microbial antagonist to disrupt nematode development inside roots is also important for achieving successful control effects in the field (Padgham and Sikora 2007). Because the female’s egg sac is completely embedded inside the root cortex, the egg sac is invulnerable to attack from antagonists that only colonize the root surface. Our results showed that A . welwitschiae significantly inhibited egg hatching by 40%. However, whether the fungus can be introduced into the rhizosphere and colonize nematode eggs remains unclear. To date, only a few host- or non-host-specific compounds are known to mediate the attractiveness of the host to the nematode. Diez and Dusenbury (1989) observed that the principle means by which nematodes locate host roots is mainly dependent on carbon dioxide or amino acids. These researchers also found that roots from tomato plants had a repellent effect on M . incognita . Similarly, Dababat and Sikora (2007) observed that root exudates from Fusarium strain 162-inoculated tomato plants also reduced M . incognita attraction and movement. Our results showed that inoculation with A . welwitschiae significantly eliminated the attractiveness of rice roots to M . graminicola . However, the inoculation of endophytic fungi into plants does not always result in repellent effects on plant parasitic nematodes (Athman et al . 2006). Le et al . (2016) observed that the root exudates from F . moniliforme Fe14-treated plants were either less attractive to or had a repellent effect on the movement of M . graminicola . Oostendorp and Sikora (1990) reported that Pseudomonas fluorescens colonization of sugar beet roots had no effect on the movement of Heterodera schachtii juveniles. These studies implied that nematode reduction may occur at the post infection stage (Le et al . 2016). Thus, further research on the possible mode of action of host-specific compounds for nematode attraction is also needed for the biological control of M . graminicola with A . welwitschiae . A further challenge in designing biocontrol systems for RKNs of rice is to evaluate the durability and efficacy of the biocontrol organisms in the field. In Southeast Asia, most rice varieties are planted in the anoxic soil conditions of flooded rice paddies. External leakage of oxygen around the rhizosphere soil is sufficient to support a number of anaerobic microbial communities in flooded soil. However, a shift in soil microbial communities of flooded rice systems may have a negative influence on the introduced fungi inside the roots, thereby decreasing the durability and efficacy of the biocontrol organisms in the field (Liesack et al . 2000; Scheid et al . 2004). In addition, the use of biocontrol agents in agriculture as alternatives to nematicides may reduce the cost of controlling various nematodes incurred by farmers. However, most biocontrol agents were demonstrated to display lower efficacies than nematicides against RKNs, preventing the use of only bioagents for nematode control (Saikia et al . 2013). Therefore, further research should focus on the combined use of biological agents and chemical nematicides to increase the reliability and efficacy of nematode control, simultaneously reduce costs for farmers and provide long-term protection against RKNs to host plants. 5. Conclusion The use of biocontrol fungi is more environmentally friendly than the use of chemical nematicides for the management of nematodes. Soil drenching with A . welwitschiae in the greenhouse had a significant control effect on M . graminicola and represents a new strategy for biocontrol of plant parasitic nematodes in rice-producing areas. However, further research should focus on the interaction mechanisms between A . welwitschiae , rice and M . graminicola to obtain a better control effect in the field. Acknowledgements This work was financially supported by grants from the National Key Research and Development Program (2018YFD0201202 & 2017YFD0201102) and the National Natural Science Foundation of China (31571986). References Athman S Y, Dubois T, Coyne D, Gold C S, Labuschagne N, Viljoen A. 2006. Effect of endophytic Fusarium oxysporum on host preference of Radopholus similis to tissue culture banana plants. Journal of Nematology , 38 , 455–460. Bridge J, Plowright R A, Peng D. 2005. Nematode parasites of rice. In: Luc M, Sikora R A, Bridge J, eds., Plant Parasitic Nematodes in Subtropical and Tropical Agriculture . CABI Publishing, Wallingford, UK. pp. 87–130. Byrd D W, Nusbaum C J, Barker K R. 1966. A rapid flotation- sieving technique for extracting nematodes from soil. Plant Disease Reporter , 50 , 954–957. Chen S Y, Dickson DW. 2000. A technique for determining live second-stage juveniles of Heterodera glycines . Journal of Nematology , 32 , 117–121. Dababat A E F, Sikora R. 2007. Influence of the mutualistic endophyte Fusarium oxysporum 162 on Meloidogyne incognita attraction and invasion. Nematology , 9 , 771–776. Diez J A, Dusenbery D B. 1989. Repellent of root-knot nematodes from exudate of host roots. Journal of Chemical Ecology , 15 , 2445–2455. Dutta T K, Ganguly A K, Gaur H S. 2012. Global status of rice root-knot nematode, Meloidogyne graminicola. African