A rapid bioassay for measuring nematode suppressive potential of anaerobic digestate

Abstract

Summary Anaerobic digestate is a byproduct of anaerobic digestion of organic materials for biogas production. Land application of digestates may provide plant nutrition and suppression of plant-parasitic nematodes. The characteristics of digestates may vary by organic substrates and digestion conditions. To measure nematode-suppressive potential, the rigour and simplicity of a radish bioassay with Heterodera schachtii was expanded. In a three-factor factorial design, three incubation environments, two growth containers and two nematode life stages as inoculum were tested. Containers with 50 g of dry sandy loam soil were inoculated with 500 second-stage juveniles (J2) of H. schachtii or with cysts with equivalent hatchable J2. One seed of radish Raphanus sativus ‘Cherry Belle’ was planted into each container, and 1 ml of drench treatment was applied. After 64 degree days (4-5 days), roots were washed and stained with acid fuchsin for nematode counting. In three experiments, food waste digestate permeate suppressed nematode root penetration in the growth chamber, glasshouse and laboratory, in cups and tubes, and following inoculation with cysts and J2. However, root penetration by J2 was more greatly reduced after cyst inoculation than after J2 inoculation. Investigations in preserving nematode cysts showed that J2 within cysts remained viable after incubation in sandy loam soil at 23°C in sealed tubes in the laboratory for 35 days. Results of the radish assay predicted nematode-suppressive potential against Pratylenchus vulnus on peach rootstock ‘Nemaguard’ in a glasshouse experiment. In summary, a straightforward rapid bioassay for measuring nematode suppressiveness of organic liquids was developed for routine use.