What was it all about?

Up until around the year 2000, Australian pear production was largely based on the rootstock Pryus calleryana D6 (D6). This had been a good stock with exceptional longevity but it had two downsides:

• Trees on D6 rootstock take up to five years to begin fruiting
• The large size of the tree that was produced by D6 rootstock rendered it unsuitable for intensive plantings.

In the early 2000s a number of new pear rootstocks were introduced to Australia. These were dwarfing and semi-dwarfing compared to D6. However there was significant industry concern that these new rootstocks would not cope with the heavier soils and high temperatures of the Goulburn Valley, where more than 85 per cent of Australia’s pears are grown.

There were also concerns that, in particular, the Quince stocks would not result in a tree large enough for the cultural systems used in the Goulburn Valley. The previous use of Quince, although limited, had resulted in smaller trees.

In 2004, the initial trees of this trial were planted, to investigate the merits of the various rootstocks in producing the common pear varieties – Packham’s Triumph, Williams Bon Cretin and Corella.

Four rootstocks were used: D6 as the control, along with BM2000, BP1 and Quince A.

Two tree training systems were imposed on the rootstock scion combinations – Central Leader and Open Tatura Trellis. The trees on Quince A were planted two years after the others.

In this project, trees of each type were evaluated for tree size, as well as yield, fruit size, fruit weight, sugar and fruit pressure.

Key findings were:

• For WBC and Corella pears, Central Leader tree training was the highest yielding system
• For Packham pears Open Tatura Trellis was the highest yielding training system
• The D6 rootstock was the highest yielding for all three scion varieties but it resulted in more limb extension growth and more water shoots in the tree - possibly resulting in more skin marks and lower packouts (skin marks and packouts were not measured). Increased cost in labour hours is also a negative of D6
• Apart from D6, the best rootstock for Packham and Corella was Quince A and for WBC it was BM2000
• For all three varieties, Open Tatura Trellis tree training delivered trees with greater cumulative yield efficiency than trees trained to the lower density Central Leader system
• The best rootstocks, in terms of cumulative yield efficiency, were:
  • For Packham: BP1
  • For Williams: BM2000 and BP1
  • For Corella: Quince A.

Note that the rootstocks that perform well in terms of yield efficiency are quite different to those that perform well in terms of yield.

A further rootstock evaluation trial was continued after this project at Tatura.