What was it all about?

From 2017 to 2022, this investment evaluated the performance of new rootstocks for the Australian citrus industry, with the goal of delivering superior and locally-adapted rootstocks to growers.

A range of rootstocks were tested in different soil and climatic conditions, so that recommendation could be made on which rootstocks that can produce higher yields and fruit quality as good as, or better than, existing rootstocks used in Australia.

A multi-stage process was undertaken by the research team involving establishing source trees, ensuring uniformity of rootstock seeds and seedlings, glasshouse screening for disease and salt tolerance, short-term preliminary field trials to evaluate horticultural performance, and longer-term evaluation in semi-commercial plantings in a range of soil, climatic and management conditions.

The trials were conducted in major regions for citrus production in the Murray Valley, Riverina, Riverland, Queensland, and Western Australia. During the program, 77 scion/rootstock combinations were tested in several trials, and another 120 scion/rootstock combinations will be planted around Australia in October 2023. Promising rootstocks were identified from the commercially orientated and industry-based trials in the major regions for citrus production. The dwarfing effect rootstocks for high density planting and the Italian rootstocks were established at the NSW DPI Dareton Research Institute. The program also initiated the establishment of the reported HLB tolerant rootstocks at NSW DPI Dareton, NSW DPI Griffith and around Australia.

The rootstock evaluation program with a range of scion varieties has been a great success. During the start of the project, six high performing rootstocks were released for the citrus industry in 2017. The rootstock seed for the six rootstocks is now available from AusCitrus. Rootstock will be available to overseas institutes under a research agreement for research purposes.

The selected Chinese rootstocks were expanded to the semi-commercial trial on processing oranges and Zao Yang was identified as the best rootstock with Valencia 5 (DV Valencia) the superior scion. The work on salt tolerant rootstock was a great success and two hybrid rootstocks 3822 (Scarlet mandarin × Poncirus trifoliata) and 3834 (Scarlet mandarin × Poncirus trifoliata) from the NSW DPI breeding program were identified as the best rootstock able to tolerate saline irrigation conditions. The dwarfing potential for high density planting was tested by introducing two Chinese rootstocks to a trial at Dareton with M7 navel and Tangold mandarin. Although the trial is not completed yet, two rootstocks (No. 24, Poncirus trifoliata and 85-24, Poncirus trifoliata) are showing promise as a potential rootstock for high-density plantings. Semi-commercial trial sites around Australia were established in 2017 with Chinese rootstocks in different soil and climatic conditions. The data collected during those trials indicate that Ghana (Poncirus trifoliata) and Tanghe (Poncirus trifoliata) are proving to be promising rootstocks for yield and Zao Yang (Poncirus trifoliata) is continuing to produce sweeter fruit in Afourer mandarins. However, another four years of data are required to complete these trials and make recommendations.

During the program, three Italian rootstocks were introduced and were budded with three scion varieties: Imperial, Nectar and Tangold mandarins. The trial was planted in 2020 and another five years of data are required to make recommendations to the citrus industry. HLB tolerant rootstocks were recently imported from the United States. These rootstocks have now been raised and will be budded with sweet orange, mandarin, and limes. The experimental plan has been finalised to establish trials at the NSW DPI research institutes at Dareton and Griffith. Trials will also be established around Australia in five states at growers’ properties. After the trial establishment in October 2023, rootstocks will be evaluated for their effects on yield, fruit quality, fruit size distribution and tree growth.