JIA-2019-11

2566 LIU Ying et al. Journal of Integrative Agriculture 2019, 18(11): 2561–2570 nematode incubation for 72 h. The juvenile mortality at the concentrations of 5× and 10×AW2017 was (86.2±4.2)% and (51.3±7.2)%, respectively, which was significantly higher than that in the PDB control treatment, (10.5±2.1)%. 3.3. Effect of A. welwitschiae on the attraction of M. graminicola to rice roots To determine whether A . welwitschiae has a direct effect on the attractiveness of roots to M . graminicola , we examined the number of attracted nematodes around and in the roots treated with A . welwitschiae or PDB. Inoculation of 2-week- old seedlings with A . welwitschiae reduced the attractiveness of rice roots to M . graminicola , resulting in a (37.3±3.1)% and (39.6±3.4)% reduction in juveniles migrating to 1.5–3.0 and 3.0–4.5 cm from rice roots, respectively, and a (64.9±5.4)% reduction in the number of J2s that penetrated the roots (Fig. 4-A). No significant difference was observed in the movement of J2s to the area 0–1.5 cm from rice roots. In the control chamber, no significant movement of J2s was detected at the same distance from rice roots (Fig. 4-B). This result indicates that the tested conidial suspension of A . welwitschiae significantly eliminated the attractiveness of rice roots to M . graminicola . 3.4. Biological control efficacy of A. welwitschiae under greenhouse conditions To evaluate the biological control effect of A . welwitschiae on M . graminicola , nematodes in rice plants drenched with conidial suspension or liquid PDB were counted in a greenhouse experiment. Drenching with A . welwitschiae conidial suspension significantly decreased root-knot galls and nematode penetrations when compared with plants inoculated with only PDB medium. The observation of nematodes in roots after staining showed that conidial suspension treatment resulted in a significant reduction in nematodes in the 5×AW2017 ((40.5±4.7)%) and 10×AW2017 ((24.8±3.2)%) treatments at 14 d post inoculation (dpi) (Fig. 5-A). Since the J3/J4 nematodes initiated typical gall formation at 14 dpi, drenching of conidial suspension also resulted in a significant reduction in root galls in the 5×AW2017 ((24.5±4.3)%) and 10×AW2017 ((17.6±2.4)%) treatments (Fig. 5-B). In addition, the Fig. 3 In vitro ovicidal (A) and larvicidal (B) effects of Aspergillus welwitschiae metabolites at different concentrations on Meloidogyne graminicola . The bars in the different graphs represent the mean±SE of data from three times with six replicates each. Values with the same letters above the bar are not signi cantly different at the P ≤0.05 level according to Duncan’s multiple range test. Fig. 4 Attraction effect after the application of Aspergillus welwitschiae metabolites to rice roots (A) or in the control (B) in a soil bioassay on Meloidogyne graminicola distribution in sand at 1.5-cm distances away from rice roots. Each chamber was inoculated with ±800 second-stage juveniles (J2s). The bars in the different graphs represent the mean±SE of data from two experiment contained four replicates each. Values with the same letters above the bar are not signi cantly different at the P ≤0.05 level according to Duncan’s multiple range test. c d d a bc b 0 20 40 60 80 100 A B PDB 5×AW2017 10×AW2017 PDB 5×AW2017 10×AW2017 4 d 8 d Hatching rate of eggs (%) d b c d a c 0 20 40 60 80 100 PDB 5×AW2017 10×AW2017 PDB 5×AW2017 10×AW2017 48 h 72 h Mortality rate of nematode (%) c e b a e e d c 0 50 100 150 Root B A 0–1.5 1.5–3.0 3.0–4.5 Nematode number Distance from rice root (cm) Control A without AW2017 AW2017-treated plants c b d a c b d a 0 50 100 150 Root 0–1.5 1.5–3.0 3.0–4.5 Nematode number Distance from rice root (cm) Control B without AW2017 Control C without AW2017