Chinese Rootstocks Show Promise in Australia

Preliminary data from an Australian research project suggest Chinese rootstocks No. 24 and 85-24 are having a dwarfing effect on citrus tree growth and will be candidates for future high-density cropping systems. Citrus Australia reported that those rootstocks have strong potential in heavy soils, and that results on deep sandy loam soil are also very encouraging.

Tahir Khurshid from the New South Wales Department of Primary Industries (NSW/DPI) Dareton Research Station is leading this Horticulture Innovation-funded project. The project is focused on evaluating several overseas rootstocks budded to a range of mandarin and sweet orange varieties. The program is spread over five Australian states with 18 trials at growers’ properties and four trials at the Dareton Research Station. 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.

According to Khurshid, size-controlling rootstocks have many benefits:

They are important for high-density orchards because they 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 more efficiently use fertilizers and chemical sprays.

Because of those benefits, growth control characteristics are being sought for most citrus breeding programs worldwide.

Along with controlling vigor, dwarfing rootstocks must also produce high yields with promising fruit quality and large fruit size, Khurshid stated. Evaluating any of these characteristics takes time, at least seven to eight years of commercial crops after planting, before any recommendations can be made on the suitability of any rootstock/variety combination.

Trials were established In September 2017 at the Dareton Research Station. Early maturing M7 navel and Tang Gold mandarin were grafted to C-54 and C-22 from the United States and to No. 24 and 85-24 from China. Tri22 and Flying Dragon were used 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 the Australian standard, Tri22.

No. 24 displayed greater dwarfing than C-54 (Figure 1) and was slightly smaller than Tri22 (Figure 2). Early data on tree growth are shown in Table 1.