This is the report from a BSPP MSc/MRes Bursary.
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Pythium species are recognised as important soilborne plant pathogens, however, some of these species are aggressive parasites of other fungi and oomycetes, and are referred to as mycoparasitic Pythium species. These have the potential to be developed as biological control agents against plant pathogens. However, there is limited information regarding the population diversity of mycoparasitic Pythium spp. present in New Zealand, especially associated with economically important horticultural crop such as grapevine.
My first objective of this study was to determine the best methods to isolate mycoparasitic Pythium species from soil collected from the Lincoln University vineyards, and to use the best methods in a more extensive North Canterbury vineyard survey to identify mycoparasitic Pythium species diversity. Additionally, the second objective was to investigate in vitro host range and mode of parasitism of mycoparasitic Pythium spp. isolates recovered from North Canterbury vineyard soils.
The first soil sampling was done in summer (Jan 2021) from the organically and conventionally managed vineyard sites at Lincoln university. Three isolation methods were tested (1) soil dilution plating, (2) sclerotia baiting, and (3) pre-colonised fungal host baiting (fungal hosts: Botrytis cinerea, Fusarium oxysporum, Ilyonectria liriodendri, Neofusicoccum luteum, and Neofusicoccum parvum). The sclerotia baiting and F. oxysporum pre-colonised plate methods were the most effective at recovering mycoparasitic Pythium species from the soil samples. Dilution plating method was the least effective method for isolating mycoparasitic Pythium spp. More mycoparasitic Pythium spp. isolates were recovered from the organically managed vineyard. The species identity of the recovered isolates were confirmed as P. acanthicum and P. oligandrum (Figure 1) using sequencies of the ITS and cox II gene regions. The six vineyards from North Canterbury (including two vineyards from summer samping) were surveyed during autumn (April/May 2021) for soil sampling, as for the summer sampling P. acanthicum and P. oligandrum were recovered from the autumn soil sampling.
The host fungal range of the P. acanthicum and P. oligandrum isolates recovered was investigated using a pre-colonised host culture assay, with four fungal hosts used B. cinerea, F. oxysporum, I. Iiriodendri and N. parvum. Of the four hosts tested N. parvum and F. oxysporum were identified as being susceptible host, I. Iiriodendri was identified at being less susceptible, and B. cinerea was identified as a resistant host. Interactions on I. Iiriodendri pre-colonised host plates indicated that P. acanthicum isolates was less aggressive than P. oligandrum. Four types of parasitic reactions being hyphal lysis (Figure 2), cytoplasmic coagulation (Figure 2), hyphal thickening, and some coiling attempts were observed when interactions between hyphae of P. acanthicum and P. oligandrum and the different host pathogens on coverslip thinly coated with water agar. Pythium acanthicum and P. oligandrum had the same mode of parasitism.
The findings of this study showed that both P. acanthicum and P. oligandrum were present in vineyard soils in the North Canterbury region of New Zealand and, with regards to grapevine trunk pathogens, have a similar host range and mode of parasitism. However further glasshouse and field experiments are required to determine their efficacy in reducing infection of grapevines by grapevine trunk pathogens.
I thoroughly enjoyed my one-year research master project at Lincoln University, New Zealand. I have developed good understanding of fungal isolation and identification techniques using morphological studies or molecular techniques. I enjoyed talks with vineyard managers about vineyard establishment and management. during vineyard soil sampling. I also gained experience of setting up an experiment for biocontrol assay and statistical analysis. Besides this, I have developed my confidence and time management skill. I would like to thank my supervisors Prof. Eirian Jones and Manjula Kularathna for their support and guidance during my master project. I am grateful to BSPP for recognising my project by awarding me with BSPP Master Bursary.
Pratima Dhakal Acharya