Enhanced Efficacy and Economic Feasibility of Anaerobic Soil Disinfestation Combined with Carbon Source and Cover Tarps in Controlling Strawberry Soil-borne Diseases

Pre-planting soil fumigation is a common practice for controlling strawberries (Fragaria×ananassa Duchesne) soil-borne diseases worldwide. Methyl bromide was the preferred fumigant for growers until it was classified as an ozone-depleting substance, and its utilization was gradually restricted and legally phased out in 2015 in China. Chloropicrin or 1, 3-dichloropropene as the main alternative fumigants for methyl bromide are not sustainable. These kinds of broad-spectrum fumigants require a commercially licensed application, are costly, and are potentially hazardous to agricultural workers and the environment. These negative side-effects have promoted the search for alternatives that growers can use to control soil-borne diseases. Anaerobic soil disinfestation (ASD) is widely evaluated to suppress soil-borne diseases economically in numerous crops. The efficacy of the ASD technique varies with the form of the carbon source and its quantity, the soil properties, the temperature, and the cover tarps. The influence of different tarps on ASD efficacy is not documented.
The structure of the thesis was divided into three parts: 1) the first part focused on optimizing ASD technologies by testing several carbon sources, cover tarps, soil moisture, and air temperature to reduce ASD cost while maintaining the efficacy; 2) using high-throughput sequencing (HTS) technologies to monitor the soil microbial communities before and after ASD treatments; 3) organizing field trials to evaluate the effect of ASD on control strawberry soil-borne diseases and the responses of plant growth, yield, and grower’s income.
In the laboratory experiments, we evaluated the efficacy of three films used for ASD. The films included: polyethylene (PE), totally impermeable film (TIF), and virtually impermeable film (VIF). Water irrigation was used as a blank control. The result indicated that the combined factors of maltose, 28℃ temperature, and 30% of soil moisture carried out for ASD were more efficient than the other conditions by orthogonal experimental studies. Also, ASD using maltose as an organic amendment and sealing with TIF obtained the higher suppression against Fusarium spp. (> 99.5%) and Phytophthora spp. (> 99.3%).
In the field trials, the efficacy of ASD using 6 and 9 t/ha maltose and sealing with TIF was evaluated and compared with reference treatment with chloropicrin (Pic), soil solarization (Sol), or untreated control. Compared with the untreated soil, ASD treatments highly reduced the colony number of Fusarium spp. and Phytophthora spp., and successfully controlled the damage caused by root rot wilt disease. ASD significantly increased the soil’s nutrition which promoted plant growth. Also, it significantly increased strawberry yield, which was similar to the Pic but better than the solar energy treatment. The analyzed fungal and bacterial microbiota did not show significant differences in the taxonomic richness and diversity between the compared treatments. Nevertheless, compared with the blank control, ASD treatments seemed to cause a modification change of the soil bacterial and fungi taxonomy composition at the class and genus levels even though the shift was not significant.
In the second field trial, to reduce the cost of ASD and to promote its commercial application, the impact of 6 tons/ha composted chicken manure (CCM, CCM6) or 12 tons/ha CCM (CCM12) and TIF against soil-borne pests was evaluated. The results showed that the colonies of Fusarium spp. and Phytophthora spp. reduced significantly after ASD. With ASD treatment, the concentration of ammonium nitrogen, nitrate-nitrogen, and organic matter was significantly increased, but the oxidation-reduction potential was decreased in the soil. Besides, the strawberry plant height, stem thickness, and yield were significantly higher than the control. The strawberry marketable income was higher with ASD, the economic benefit could be due to the suppression of soil-borne disease reduction and the improvement of soil nutrition. The soil bacterial and fungal diversity and richness increased after CCM 6 treatment, but there was no significant difference between the CCM12 and the control. The increased biological control agents lead to the suppression of soil-borne pathogens.
In summary, the results of the three experiments showed that adding maltose or compost chicken manure as a carbon source and coupling it with TIF for ASD has a great potential to replace chloropicrin for soil-borne diseases control in commercial strawberries production.