Evaluating the in vitro efficacy of Abamectin and Fluopyram, alongside hot water treatments against Meloidogyne incognita and Globodera rostochiensis : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Applied Science at Lincoln University

Abstract

Plant germplasm importation into Aotearoa/New Zealand poses a risk of introducing unwanted organisms. Current biosecurity measures for plant nematodes on imported nursery stock are under review. This study aimed to investigate alternative chemicals that could replace fenamiphos, the current border treatment. Abamectin and fluopyram were chosen for assays based on their demonstrated nematocidal activity and availablity. Hot water submersion was also tested as a non- chemical alternative. Pratylenchus sp. were extracted from field samples and identified using morphology and molecular methods. Cultures of Meloidogyne incognita and extraction of Globodera rostochiensis cysts were successful, but Pratylenchus sp. cultures could not be established. Preliminary experiments tested the field rates of abamectin (0.009 g/L a.i) and fluopyram (0.3 g/L a.i.) individually and in combination, along with two fenamiphos concentrations (2 g/L and 40 g/L). Abamectin and fluopyram resulted in paralysis rates of ≥ 66.7% in M. incognita J2s, while fenamiphos exhibited no significant differences from the negative control. All treatments produced reversible effects on J2 immobility, indicating a nematistatic effect. Hot water experiments at 44°C for 3 hours caused complete and irreversible paralysis in M. incognita J2s. Further experiments using varying concentrations of abamectin and fluopyram on M. incognita J2s, indicating the highest paralysis rate with abamectin (0.09 g/L a.i.) was 75.2%, while concentrations of fluopyram ≥ 0.6 g/L resulted in 100% paralysis. All combined concentrations of abamectin and fluopyram resulted in 100% paralysis, as did hot water treatments for 1 and 2 hours at 44 and 50°C. In preliminary experiments, no chemical treatments achieved complete mortality in G. rostochiensis juveniles, and no significant differences were observed in the proportion of immobile juveniles compared to the negative control. Hot water treatments at 44°C for 3 hours, in combination with abamectin, fluopyram, abamectin and fluopyram together, and 40 g/L fenamiphos, completely immobilized G. rostochiensis juveniles 48 hours after treatment. Retrospective analysis found the G. rostochiensis experiment results inconclusive due to assessing viability based on movement rather than more precise methods. A preliminary trial using Meldola blue stain revealed that live G. rostochiensis juveniles remained unstained, while dead juveniles stained when exposed to 0.05% Meldola blue for 3, 5, and 7 days. This method was incorporated into further G. rostochiensis experiments. Further chemical experiments on cysts showed no differences compared to the negative control of RO water based on the proportions of juveniles stained with Meldola blue. Hot water treatments at 44°C and 50°C for 1 and 2 hours caused a lower percentage of deceased juveniles compared with the negative control of 24°C. Further experimentation using in planta bioassays are recommended to assess how the chemicals affects nematodes contained within plant tissues as well as plant viability. Expanding the research to encompass a broader range of nematode species is also recommended. Overall, the study demonstrated the potential of abamectin, fluopyram and hot water submersion which provided the complete mortality required in biosecurity situations as alternatives to fenamiphos for biosecurity measures in Aotearoa/New Zealand.