Australia Evaluating Dwarfing Rootstocks

Jim Rogers International, Research, Rootstocks

Tahir Khurshid of Australia’s New South Wales Department of Primary Industries (NSW DPI) is leading a project evaluating several overseas rootstocks budded to a range of mandarin and sweet orange varieties. One of the components is evaluating the rootstocks for their dwarfing effect, which will potentially produce small trees for high-density planting systems for the citrus industry.  

Rootstocks
Four-year-old navels are growing on No. 24 (left) and C-54 (right) rootstocks at a density of 800 trees per hectare at the Dareton research station.

Size-controlling rootstocks have many benefits:

  • They are important for high-density orchards, as these plantings crop earlier and produce high yields due to many trees per unit of land.
  • Harvesting smaller trees is more economical than harvesting larger trees.
  • Smaller trees can have more efficient use of fertilizers and chemical sprays.

Flying Dragon (Poncirus trifoliata) rootstock is a dwarfing rootstock that is commercially available for the citrus industry. However, this rootstock is very slow growing when grafted to navel oranges. It takes a few years to produce a commercial crop, and the yield is too low for too long, even if planted at higher densities. Therefore, a size-controlling rootstock that is faster growing and produces greater yields than scions grafted to Flying Dragon is needed.

In September 2017, trials were established at the NSW DPI Dareton research station. Early maturing M7 navel and Tang Gold mandarin were grafted to C-54 and C-22 (from the United States) and No. 24 and 85-24 (from China) using Tri22 (the Australian standard) and Flying Dragon as controls to find a superior rootstock with dwarfing tendency. Tree density is 800 trees per hectare. The effect of these rootstocks on tree growth, yield and fruit quality is being evaluated in comparison to Tri22.

Preliminary data suggest the Chinese rootstocks No. 24 and 85-24 are having a dwarfing effect on tree growth and will be candidates for future high-density cropping systems.

The program is spread over five Australian states with 18 trials at growers’ properties and four trials at the Dareton research station.

In Georgia in the United States, most citrus is grown on Poncirus trifoliata rootstocks such as Rubidoux, Rich 16-6 or Flying Dragon. Learn more about rootstock trials in Georgia.

Source: Citrus Australia

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