Earthworm combined with Bacillus velezensis improves bacterial community structure and the control effect of Fusarium wilt diseases of continuous cropping lily

Objectives We studied the effect and mechanism of earthworm and biocontrol bacteria strain on improving physiochemical properties, and microbial structure and diversity in rhizosphere soil of continuous cropping lily, to propose an effective measurement to alleviate the impaction of Fusarium wilt diseases on the industry of lily production in Hunan Province.

Methods A pot experiment was conducted in Changsha City, Hunan Province. The test crop lily (Lilium lancifolium Thunb.) was cultured in 2019 and 2020 continuously. The test bacteria strain was Bacillales velezensis YFB3-1 liquid (bacterial concentration ×10⁹ CFU/mL), and the earthworm was Eisenia fetida. The four treatments included neither applying bacteria nor earthworm control (CK), merely applying bacteria liquid (T1), earthworm (T2), and the combination use of bacteria strain and earthworm (T3). The yield and Fusarium wilt diseases of lily were investigated. The rhizosphere soil were sampled after the harvest of the second lily crop for the determination of soil physiochemical properties, bacterial community structures and diversities.

Results Compared with the first crop, the yield of the second lily crop of the same treatment was significantly reduced. The highest yield of lily was all recorded in T3 treatment in 2019 and 2020 two years (16464 kg/hm², and 15674 kg/hm², respectively), which were significantly (P<0.05) higher than the other treatments in the same year. The diseases incidence and disease index was the lowest in T3 treatment (18.15 and 25.00, respectively) in the two years as well, which were significantly (P<0.05) lower than those in the other treatments in the same year. T3 treatment had stronger control effect on lily wilt diseases (P<0.05) than T1 and T2 treatment did in two years. The lily wilt diseases incidence in T3 treatment was 44.55% and 37.66% lower than in CK, and the lily yield was 15.05%, and 14.78% higher than in CK in 2019 and 2020. T3 treatment increased the population abundance of beneficial microorganisms such as Rhizobiales, Flavobacteriales, Pseudomonadales and Bacillales in the rhizosphere soil of lily, and the bacteria strain and earthworm showed significant interaction effects in inhibiting Fusarium wilt diseases of continuous cropping lily, thus alleviated the yield decline of continuous cropping lily.

Conclusions While using Bacillus biocontrol agent to control the continuous cropping lily wilt diseases, farmers should increase the number of earthworms by applying organic fertilizer (cow dung), for better preventing effect of the lily wilt diseases and less yield loss of continuous cropping lily.