Biochar reduced the suppressive effect of composts on potato cyst nematodes

Potato cyst nematodes (PCN) are one of the most damaging pests to potato production. Among management measures, the use of soil amendments has been a traditional practice to reduce plant-parasitic nematodes, including PCN. The objectives of this study were: (1) to investigate the effects of two concentrations (0.3% and 1% V/V) of two types of biochar and compost on survival and reproduction of Globodera rostochiensis and G. pallida and (2) to understand the modes of action of these amendments in PCN suppression by exploring their effects on hatching and infectivity of second-stage juveniles (J2). The treatments included biochar 1 and biochar 2 (produced by slow pyrolysis of wood at 480°C, and holm oak wood at 650°C, respectively) alone, biochar 1 mixed with wood chip compost after the composting process, biochar 2 blended with a mixture of green and municipal waste before the composting process and either composts alone. Soil amendments were mixed with a sandy soil; non-amended soil served as a control. Cysts of either species were placed in retrievable bags and added to the soil in a pot either planted with potato (reproduction test) or without potato (survival test). The viability of cysts content was determined after 8, 12 and 16 weeks using the trehalose-based method. PCN reproduction was determined at potato harvest 16 weeks after inoculation by counting new cysts and their content. To study the impact of amendments on hatching, batches of 20 cultured cysts of each PCN species were exposed for 10 weeks to potato root diffusate collected from non-amended and amended soils and the percentage of hatched J2 was calculated. To examine the effect of amendments on J2 infectivity, batches of 3000 freshly hatched J2 of either species were added to pots planted with potato in amended or non-amended soils. The number of J2 inside the roots was determined 10 days later. Incorporation of either composts alone reduced egg viability, reproduction, hatching and infectivity of PCN. Addition of both biochar types did not have any effect on PCN species; moreover, it inhibited the suppressing effect of both composts on PCN irrespective of the time of mixing biochar with the composts or the dosage. The composts probably released products or triggered changes in the rhizosphere that killed eggs and juveniles, or changed the physiology of the roots leading to reduced hatch and lower root penetration. In conclusion, amending soil with biochar is not recommended when a potato field is infested with Globodera species, while compost application may be beneficial.

Key words- amendment, viability, reproduction, hatching, infectivity