| Root-knot nematodes (RKN, Meloidogyne sp.) are harmful to the agricultural production in the worldwide. With the popularization of greenhouses cultivation, the RKN disease happens more extensively and severely than ever before. Since RKN are protected by a thick collagenous cuticle from attack and have very broad hosts that cover almost all common crops and weeds, the prevention and control of nematode damage are very difficult. Although chemical control of RKN is efficient, it has been gradually banned because of its danger to safety of human and environment. Physical controls (e.g., solarization of soil) and agricultural management (e.g., using crop rotation and resistant new cultivars) are safer than the chemical ways, but unfortunately, their application is limited by environmental conditions and the effect is unsatisfactory. Envrioment-friendly biological control becomes a potential substitute method for control of RKN. This study is aimed to screen effective antagonists against RKN, to prepare anagonist-enhanced bio-organic fertilizers and to evaluate the effectiveness of the bio-organic fertilizers both in greenhouse and in field.We had proposed a hypothesis that if collagen in the cuticle of RKN was decomposable to bacteria, the activity and infectivity of second stage juvenilis (J2) would be reduced and J2 even would be injured. We screened the bacteria from soil that could produce collagenase by the selective medium and got two strains named QL17 and ZY5. After culturing 48 h on the gelatin plate, the colony diameters of QL17 and ZY5 were 3.67 mm and 6.60 mm, respectively, while their diameters of gelatin hydrolysis zone were 16.8 mm and 22.5 mm, respectively. Taeated with the 1/5 strength of bacterial culture filtrate, the J2 mortality by QL17 and ZY5 were 52.49% and 65.52%, respectively, after 48 h of incubation. QL17 and ZY5's morphological and physiological features as well as the 16S rDNA sequences were analyzed according to the Bergey's Manual (8th) and Common Bacterial Systems Identification Manual and identified as Bacillus megaterium strains.A greenhouse experiment was carried out for investigation of the biological control effect of the antagonists on RKN in tomato. The mixture of an amino acid fertilizer and pig manure compost with addition of different strains in more than 108 CFU·g-1 was composed to prepare bio-organic fertilizers. Compared with the control of chemical fertilizer, the bio-organic fertilizers strengthened with strain QL17 and strain ZY5 significantly reduced: (1) the gall indice with 63.5% and 48.9% of relative control efficiency, respectively; (2) the density of J2 in soil of both treatment by 45% at 60 d after transplanting; (3) the eggs in 1 g fresh root by 27% and 24%, respectively. All the results showed that bio-organic fertilizers contained the antagonist QL17 and ZY5 could prevent the plants from RKN attack and suppress the reproduction of RKN。A field experiment was carried out in the RKN severely infected soil of muskmelon including 4 different bio-organic fertilizers,i.e., three of them were fermented separately by two Bacillus strains X5 and BTG and a Trichoderma strain (supplied by our laboratory), one of them was made by the mixture of the prior three bio-organic fertilizers at ratio 1:1:1. Results were as follows:(1) the incidence of RKN was significantly reduced in the treatments of bio-organic fertilizers with the highest control efficiency of 81.14%, whereas the chemical fertilizer control is heavily diseased; (2) application of bio-organic fertilizers effectively reduced the population of second stage juvenilis in soil, eggs per eggmass and eggs in root system; (3) the DGGE patterns of nematodes from the soil treated with bio-organic fertilizers and common fertilizers belonged to two corresponding clusters, suggesting that application of bio-organic fertilizers contained the antistatic strains of RKN changed the structure of nematode community in soil. |
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