Evaluation of Photosynthesis on Winegrapes

McArtney S., Ward S., Dayatilake G. A. and Wünsche, J.N.

for HortResearch, Hawkes Bay

Report to Garuda Homeopathics Ltd (edited for presentation)

Contents

Executive Summary

Introduction

Methods

Results and Discussion

Conclusions

Executive Summary

In 2003, one Garuda Homeopathics Ltd. product; 'PhotoMax' was evaluated in a trial on Cabernet Sauvignon winegrapes growing in a commercial vineyard in the Hawke's Bay region.

These trials revealed significant positive effects on vine physiology (leaf photosynthesis).

•  'PhotoMax' consistently increased the rate of leaf photosynthesis, measured one or two days after treatment. This increase was in the order of 20% compared to a water-treated control. However, there was no effect of 'PhotoMax' on any of the juice quality parameters measured (soluble sugars, pH, or titratable acidity). The lack of any effects on juice quality may be attributed to the poor climatic conditions during the month leading up to harvest and/or the heavy level of grapevine leafroll virus infestation in the vines used in this study. Research with 'PhotoMax' should be carried out on healthy vines for at least one further season to establish whether any positive fruit quality responses can be achieved in a more favourable season (climate wise).

For further information contact:
Dr Steven J. McArtney
HortResearch
Private Bag 1401
Havelock North, New Zealand
Tel: +64-6-877 8196
Email: smacrtney@hortresearch.co.nz

Introduction

Organic exports from New Zealand exceeded $70 million in 2002, these exports were primarily kiwifruit, processed vegetables and apples. Approximately 9% of apple orchards are currently fully certified for organic production. With increasing volumes of organic production, numerous biodynamic preparations have become available for use within the horticulture sector. Both organic and non-organic producers have an interest in the potential benefits these preparations offer. Whist these preparations are claimed to have efficacy in improving plant growth and health and/or controlling various pests and diseases, these claims have seldom been independently tested and verified.

The objectives of this project were to:

•  Assess the effect of ‘PhotoMax' on vine physiology and fruit quality when sprayed independently

Methods

Fruit Ripening Study

PhotoMax was applied as a dilute spray (equivalent to 800 L spray mix per hectare) to 5-vine plots of mature Cabernet Sauvignon vines using a motorised knapsack sprayer. A water control was included for comparative purposes. Four replicates of each treatment were arranged in a randomised block design. The treatments were applied on three dates (7 March, 19 March and 3 April 2003) at the recommended label rates.

Table 1. Description of ripening treatments applied to mature Cabernet Sauvignon grapevines in Hawke's Bay.

A random fruit sample was removed from each plot of five separate dates leading up to harvest (7 March, 19 March, 26 March, 2 April and 9 April 2003). A juice sample was extracted on each sampling date after combining five bunches per plot (one bunch per vine). Measurements made on the fresh juice sample included soluble sugars (Atago Model PR100 digital refractometer) and pH (Metrohm Model 744 pH meter). After dilution was distilled water (1:5), a portion of this juice was stored frozen for subsequent measurement of titratable acidity (Metrohm Model 716 DMS Titrino).

Treatment effects on the rate of leaf photosynthesis were measured on two dates (21 March, 4 April 2003), two and one days after the second and third treatment applications, respectively. Photosynthesis was measured on two leaves per plot using a portable photosynthesis measurement system (CIRAS-1, PP Systems, Herts, United Kingdom) at ambient CO2 saturated photon flux density (1400 umol.m-2.s-1), and ambient air temperature.

Data were analysed by general linear model procedures using the SAS statistical software (Version 8).

Results and Discussion

Fruit Ripening Study

Photosynthesis
The vines used for the fruit ripening study were badly infected with grapevine leafroll virus, which typically results in delayed fruit maturity. On red grapes, such as Cabernet Sauvignon, established virus infection is easy to identify late in the season as it turns leaves red. The distribution of virus within the block and hence within the treatments was consistent, so the presence of the virus was not considered to have influenced the relative differences determined between treatments. Leaf photosynthesis and stomatal conductance were measured on two leaves per plot. On the first measurement date one of the sample leaves exhibited grapevine leafroll virus symptoms while the other sample leaf did not exhibit symptoms. The rate of photosynthesis in leaves exhibiting grapevine leafroll virus symptoms was only 25% of the rate of leaves showing on symptoms (data not shown). Averaging the data from leaves exhibiting grapevine leafroll virus symptoms and those not showing symptoms, ‘PhotoMax' significantly increased (21%) the rate of leaf photosynthesis on 21 March 2003 (Table 3). On the second measurement date (4 April 2003) the two leaves chosen per plot did not exhibit grapevine leafroll symptoms. Again ‘PhotoMax' significantly increased (17%) the rate of leaf photosynthesis. The positive effects of ‘PhotoMax' on leaf photosynthesis were related to an increase in stomatal conductance. The combined treatment led to an increase in leaf photosynthesis which was similar to that achieved with the ‘PhotoMax' alone.

Table 3. Effects of whole-vine sprays of “PhotoMax', on saturated rate of leaf photosynthesis (Pn, umolCo2.m-2.s-1) and stomatal conductance (Gs, mmolH20.m-2.s-1) of Cabernet Sauvignon grapevines.

Fruit maturity
The rate of accumulation of soluble sugars was rapid between the first two sampling dates, but then slowed and failed to reach 20% for any treatment. In most seasons in Hawke's Bay Cabernet Sauvignon is harvested at a soluble sugar concentration of 21-22%. The vines in the present study never accumulated more than 20% soluble sugars: this could have been a result of the poor season and/or the extent of grapevine leafroll virus infection. The positive effect of ‘PhotoMax' on the rate of leaf photosynthesis was not translated into more rapid accumulation of soluble sugars in the juice. It was estimated that fewer than 20% of the leaves were free from leafroll virus symptoms, so that any treatment effect on leaf photosynthesis would have minimal impact on the carbon economy of the whole vine. There were no treatment effects on either pH or titratable acidity of juice

Conclusions

There were some significant positive effects of the biodynamic products used in these studies on vine physiology and fruit quality.

•  ‘PhotoMax' consistently increased the rate of leaf photosynthesis, measured in the first one or two days after treatment. This increase was in the order of 20% compared to a water-treated control. However, there was no effect of either ‘PhotoMax' on any of the juice quality parameters measured (soluble sugars, pH, or titratable acidity). The lack of any effects on juice quality may be attributed to the poor climatic conditions during the month leading up to harvest and/or the heavy level of grapevine leafroll virus infestation in the vines used in this study. Research with ‘PhotoMax' should be carried out on healthy vines, for at least one further season to establish whether any positive fruit quality responses can be achieved in a more favourable season (climate wise).