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Case Study

Kiwifruit stump root trial

Braden Hungerford, MJF Orchard, Te Puke.
Gerard Besamusca, AgConsult, Waihi.
Karin Watson, BioCult, Cambridge.
Simon Budd, BioStart, Tauranga.
Jerome Demmer, BioStart, Auckland.
Ranfurly Orchard Services, Te Puke.

31 August 2012


Overview

The recent discovery and impact of Pseudomonas syringae pv actinidiae (Psa) on kiwifruit has meant that a number of kiwifruit orchards will be regrafted this year with more resistant varieties (e.g. the G3 gold kiwifruit cultivar). As part of this regrafting process, the scions (leaders?) in Psa‐affected orchards will be removed by cutting the trunk below the grafting joint which will have a severe impact on the vine root system. When the vine is regrafted, the much smaller canopy in the first year or two after regrafting will leave root/shoot system unbalanced in the orchard. It may take at least one full growing season before the canopy can produce adequate levels of photosynthetic material in order to sustain the requirements of the large root systems left behind after cutting the trunks. This will impact the vine by reducing root exudates, which in turn affect soil biology in the root zone, and thereby increase the chances of root diseases impacting the vine health.

Mycorrcin is a BioStart product that has been extensively tested and is widely used in grapes and other horticultural crops to promote root health and vigour. The effects of Mycorrcin are achieved through promoting root health and root‐mycorrhizal fungal associations in a target plant. In this Project a kiwifruit trial was conducted using Mycorrcin in order to measure the impact of this product on kiwifruit vine health and minimise the effects of canopy reduction in an orchard re‐grafting programme.

Particular aim of the Mycorrcin trial was to determine whether this product promoted soil biological activity, in particular of mycorrhizal fungi, around the roots of kiwifruit vine trunks in orchards that are being re‐grafted. Mycorrhizal fungi form mutually beneficial symbiotic relationship with plant roots. Earlier trials in kiwifruit had shows Mycorrcin also promotes lateral root branching resulting in more actively growing root tips, as well as enhancing nutrient uptake.

Methodology

Trial Design: The trail was conducted down in a commercial kiwifruit orchard using blocks C2 and C3 in MJF Orchard in Te Puke (see Map 1). The soil in the orchard is Te Puke sandy loam (Ngak_2.1) with sprinkler irrigation being installed across the orchard. The orchard consists of Hort 16a kiwifruit (planted 2006) grown on a pergola strip male system. The variety was the cut back to below the graft (late September 2011) and left to grow rootstock suckers (Bruno) to be regrafted this season (Zespri G3 ). There were four untreated and four treated replicate blocks. Within each block 4 trenches were dug at the end of the growing season to monitor effects on the roots. Vine regrowth was reflected in shoot growth of between 2 and 4 m length.

Product Application: There were two applications of Mycorrcin made in the trial. The first application was carried out on 10 January 2012 using a commercial floodjet sprayer applying it at a rate of 6 ltrs Mycorrcin/ha in 1,500 ltrs water/ha. The Second application was carried out on 5 March 2012 using a commercial floodjet sprayer applying it at a rate of 4 ltrs Mycorrcin/ha in 1500 ltrs water/ha.

Root Measurements: On 2 May 2012 small trenches were dug next to 32 vines in the orchard; 16 treated and 16 untreated. Each trench was dug ~200 mm from the trunk, and about 500 mm deep and 1,000 mm wide. A 7x3 grid was used to assess roots in the trench walls. Grid squares were 125x125 mm. Roots were counted in each square and placed into three categories according to root size; large roots > 100 mm, medium size roots 2‐10 mm, small roots <2 mm).

Root samples were collected from each vine to determine the levels of ectomycorrhizal (EM) as well as vesicular abuscular mycorrhizal (VAM) colonisation, root branching, active root tips, nematode damage.

Data collected from these measurements were analysed using t‐tests.


Results:

Map 1: Outlay of the trials and approximate position of sampled vines.

kiwi_mycorrcin_xtable.jpg

 

Root measures being made in the orchard (Below):

kiwi_mycorrcin1_phto1.jpg



Figure 1: Effect of Mycorrcin on Kiwifruit Vines. NB the error bars are ± 1 x SEM


kiwi_mycorrcin_graph.jpg


Mycorrcin Significantly increase small root numbers

The Mycorrcin treatment of kiwifruit vines produced a statistically significant 42 % increase (p <0.003) in the number of small roots per plant from 22 to 31 small roots per vine in the area sampled for control and Mycorrcin treated vines, respectively (Figure 1). Similarly, Mycorrcin treatment produced a 13 and 29 % increases in the number of medium and large sized roots per vine, respectively, but these increases were not statistically significant (p < 0.355 and p < 0.341, respectively).

The analysis of the root numbers for the three different root sizes in the orchard showed that there was variability between individual vines within the same treatments and this has impacted on some of the statistical significance of differences between control and treated means. We think this variability may in part be attributable to the different subsoils present in the orchard.

Further analysis of the effects of Mycorrcin treatment showed that the increase in small root numbers was 42 and 39 % in the top two soil layers analysed 0‐125 mm (p <0.021) and 125‐ 250 mm (p< 0.035) layers, respectively (Figure 2). Although increases in root numbers were observed for medium and large roots in some of the layers these differences were not statistically different from control root numbers (Figure 2). The difference in root numbers for each layer and root size between control and Mycorrcin‐treated vines is presented in Table 1.


Table 1

The Effect of Mycorrcin on Kiwifruit Vine Roots in Different Soil Layers Expressed as Difference from the Control Vines.

Sample depthSmallMediumLarge
0-125mm42%20%48%
125-250mm39%-7%-6%
250-375mm74%68%-33%

 

Figure 2 Effect of Mycorrcin on Kiwifruit Vine Roots in Different Soil Layers. NB the error bars are ± 1 x SEM

kiwi_mycorrcin_graph2.jpg


Root Microbial Interactions
Further root analysis was carried out by BioCult and this is summarised in Table 3.


Table 2 – Root Analysis Results

Root branches/g fine roots% Active white root tipsNematode root damage% EM colonization% VAM colonization
Control8463%0.03099%91%
Treated9659%0.02498%96%
Difference12-5%-0.006-2%5%
Diff as % of control14%-7%-21%-2%5%

Mycorrcin treatment of vines increased the amount of root branching by 14 % when compared to untreated vines, reflecting what was observed in the small root count numbers. This difference was not statistically significant.

There was a small drop in the percentage of active white root tips. It is surmised that in terms of absolute number of active white root tips there would still have been an increase. There was a small non‐significant decrease in white root tip numbers following Mycorrcin treatment.

Mycorrcin treatment of vines decreased the amount of nematode damage to roots by 21 % when compared to untreated vines, reflecting an in‐field observation of reduced nematode damage to roots. This difference of nematode damage was not statistically significant.

The reduction in nematode damage could be influenced by the improved mycorrhizal colonisation, which is known to have a protective effect against nematodes or by to plantmicroorganism‐ nematode signalling pathways.

kiwi_mycorrcin_phto2.jpg

The levels of EM and VAM colonisation in control kiwifruit vines was very high, 99 and 91% respectively, and these levels were not affected significantly by the Mycorrcin treatment.

The Mycorrcintreated roots showed a small decline in EM counts (1.7%) and a 5.1 % increase in VAM colonisation. 

Vine biomass

Vine biomass was weighed for all 16 vines. Mycorrcintreated vines had a statistically nonsignificant (p<0.266) 23 % increase in vine biomass over controls (1.8 versus 2.2 kg/vine for controls and treated vines, respectively).

Leaf Mineral Test
Leaf mineral analysis of the vine material showed that there were increases in vine nitrogen, phosphorous, potassium and sulphur levels (Table 3).


Table 3 – Vine lead compositions Analysis Results

ControlMycorrcin TreatedMycorrcin TreatedMycorrcin Treated
Medium RangeAvgAvgDifference% of Control
Nitrogen %2.0-2.72.12.30.210%
Phosphorus %0.18-0.300.150.230.0853%
Potassium %1.8-3.01.11.30.218%
Sulphur %0.3-0.60.580.630.059%
Calcium %2.5-4.04.054.390.348%
Magnesium %0.35-0.700.520.540.024%
Sodium %0.00-0.05<0.01<0.01
Iron mg/kg56-1504643-3-7%
Manganese mg/kg50-200156148-8-5%
Zinc mg/kg15-305257510%
Copper mg/kg7-123640411%
Boron mg/kg30-50272700%
Chloride %0.6-1.66558-7-11%

Conclusion:

  • This trial has shown that Mycorrcin treatment of kiwifruit vines resultsin a significant (42%, P<0.003) in the numbers of small roots in the top 25cm of orchard soil. Other impacts of Mycorrcin included;- increased root branching, reduced nematode damage and increased root branching.

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