Dr Solomon Wante

 

Introduction

As climate change continues to impact wine regions in New Zealand and worldwide, grape production faces unprecedented challenges. As reported by the National Institute of Water and Atmospheric Research (NIWA), increasingly unpredictable weather patterns have shown peaks of drier conditions in 2020, 2023, and 2024 at various locations across New Zealand, putting immense pressure on vineyards. To sustain future grape production and maintain wine quality, it is crucial to explore innovative strategies that enhance grapevine resilience. One promising approach is harnessing the potential of soil-beneficial microbes, particularly those belonging to the genus Trichoderma, which may improve drought tolerance and water use efficiency in grapevines.

Trichoderma: A fungal ally in the soil

Trichoderma is a genus of fungi naturally found in soils across New Zealand. Known for their ability to promote plant health, these fungi have been extensively studied for their role in biological control, where they suppress plant pathogens. However, recent research has revealed that Trichoderma species can do much more than protect plants from disease. They also have the potential to enhance plant growth and resilience, particularly under stressful conditions like drought. Grapevines, especially those grown in regions prone to soil water deficits, could greatly benefit from the support of these beneficial fungi. Applying Trichoderma around grapevine roots has the potential to boost soil biology, supporting vine productivity in the face of limited soil moisture.

 

Figure 1. Young, grafted Sauvignon Blanc grapevines grown in pots under controlled glasshouse conditions.

Summary of methods

The pilot trial was conducted by Bragato Research Institute (BRI) in collaboration with the Department of Agriculture Science at Lincoln University. We investigated the effects of Trichoderma on young, grafted Sauvignon Blanc grapevines. The experiment carried out under controlled glasshouse conditions (Figure 1) involved growing the grapevines in various soil types and subjecting them to regulated drought stress.

One example is the Temuka_50a.1 soil from Marlborough, classified as Typic Orthic Gley Soil. This clay soil is known for its high structural vulnerability and water-holding capacity, often experiencing intermittent waterlogging and gleying. While root penetration can reach up to 700 mm, moisture extraction becomes increasingly difficult as the soil dries. The objective was to determine whether inoculating Trichoderma around the root zones in soil influences soil biology in a way that enhances drought resilience and water use efficiency in grapevines, offering a potential solution for vineyards facing drier conditions.

Young grafted Sauvignon Blanc grapevines were planted in four different soil types, each representing a distinct growing environment. For each soil type, two sets of plants were established: one treated with Trichoderma and a control set without fungal inoculation. By comparing these sets under drought conditions, we identified differences in the grapevines’ ability to cope with water stress.

To better understand how Trichoderma influences grapevine resilience, we employed long-read amplicon sequencing to characterise the soil microbial communities before and after Trichoderma application in both drought and non-drought treatment sets. This technology allowed us to analyse the bacterial and fungal populations in the soil, providing insights into how Trichoderma interacts with other microbes and influences the overall microbial ecosystem around the root zones.

Findings

Soil microbes

The soil microbial analysis conducted before Trichoderma inoculation showed that Trichoderma was not among the top 10% of core fungal genera across the various soil types used in this trial. For instance, in the Temuka_50a.1 soil, classified as Typic Orthic Gley Soil, Trichoderma was significantly less abundant compared to other dominant fungi, such as Leptosporella (see Figure 2). However, after Trichoderma treatment, there was a noticeable shift in the composition of both bacterial and fungal populations. These changes suggest that Trichoderma may help foster a more favourable microbial environment, enhancing the presence of beneficial microbes while suppressing potentially harmful ones.

Figure 2. Core fungal genera in Temuka_50a.1 Soil (Typic Orthic Gley Soil) before Trichoderma inoculation

Trichoderma’s impact on drought tolerance and water use efficiency

Grapevines treated with Trichoderma exhibited enhanced growth performance under both drought conditions and normal irrigation compared to those without Trichoderma inoculation. The Trichoderma-treated vines developed superior root systems, producing more root biomass and maintaining growth with less water. This improvement is particularly beneficial in water-scarce regions, where it allows vineyards to sustain productivity with reduced irrigation (see Figure 3).

The enhanced root development is due to Trichoderma’s action in several ways: it increases below-ground biomass by solubilising phosphates and other essential nutrients, making them more available to plants; it produces plant hormones such as auxins, which stimulate root growth; and it enhances resistance to soil-borne pathogens by creating a protective barrier against them. These mechanisms collectively improve root function and water efficiency.

Despite these benefits, no significant differences were observed in physiological functions such as stomatal conductance and photosynthesis rate between Trichoderma-treated and untreated plants, whether under drought stress or normal irrigation, during the six months of the trial. Stomatal conductance measures the rate at which carbon dioxide enters and water vapour exits the leaf through stomata, and photosynthesis rate indicates the efficiency of photosynthesis, the process by which plants convert light energy into chemical energy. This suggests that while Trichoderma positively impacts root development and nutrient uptake, the effects on above-ground growth and physiological functions may take longer to manifest.

Figure 3. Improved root morphology in Temuka_50a.1 soil (classified as Typic Orthic Gley Soil) treated with Trichoderma and non-treated, under normal irrigation (a & b), and treated and non-treated with Trichoderma under drought conditions (c & d).

Conclusion

The trial has demonstrated the potential of Trichoderma as a promising tool for managing drought stress in grapevines. The study showed that Trichoderma inoculation significantly improved root development, resulting in better growth performance under both drought and normal irrigation conditions. This enhancement is largely attributed to Trichoderma’s ability to increase below-ground biomass, solubilise essential nutrients, and provide protection against soil-borne pathogens.

While the trial observed no immediate significant changes in physiological functions like stomatal conductance and photosynthesis rate within the first six months, the improved root structure suggests that Trichoderma may offer long-term benefits for grapevine productivity, particularly in water-scarce regions. These findings underscore the potential of Trichoderma to support sustainable viticulture practices and enhance resilience against climate-induced water stress. Further research is needed to fully understand the long-term effects on above-ground growth and overall vineyard productivity.

Acknowledgements

Thank you to the contributors of this research: Dr Cen (Yusmiati) Liau; Bhanupratap Vanga; Dr Annabel Whibley; Dr Amy Hill, Dr Ellie Bradley; Dr Darrell Lizamore; Dr Hossein Alizadeh and Prof. John Hampton. We also extend our gratitude to the Marlborough Grape Growers Association, Dr Stewart Field from Nelson Marlborough Institute of Technology and Yuichi Ando from Bragato Research Institute for their valuable in-kind contributions.