What was it all about?

Rootstocks have a major impact on the horticultural performance of citrus scion varieties and consequently influence the health and productivity of a citrus industry. The use of improved rootstocks is an important step for achieving a more productive and competitive industry.

Australia’s citrus rootstock improvement program is a multi-stage process involving glasshouse screening for seed characteristics, seedling uniformity, graft compatibility, disease resistance and salt tolerance, followed by orchard evaluation with a range of scion varieties.

Orchard evaluations are conducted in two phases comprising short-term trials (up to 10 years) to identify candidates for entry into longer-term semi-commercial based plantings in collaboration with industry.

This project, which ran between 2008 and 2013, involved short-term assessments of horticultural performance to identify superior rootstocks that can be entered into longer-term industry-based commercial evaluation plantings under a range of soil, climatic and management conditions.

The rootstocks evaluated in these trials, from China and from CSIRO’s breeding program had been screened previously by NSW DPI and CSIRO for disease resistance and salt tolerance.

Rootstock effects on tree growth, fruit yield and quality were assessed over a period of five years continuing work from four trials established in 2001 of Navelina, Lane Late navel, Imperial mandarin and Eureka lemon. Root excavation was also carried out in trees from stages 1 and 2 to investigate root distribution and structure.

Based on cumulative fruit yield, size and internal quality, as well as tree size, a number of rootstocks were selected from stage 1 according to their effects on different scion varieties.

Data presented in the final report details rootstock effects on the performance of trees for tree establishment, growth, chloride uptake, disease resistance, fruit yield and quality. Data concerning tree growth, fruit yield and quality are reported for the second and third stages, while data for chloride uptake are reported for trees in three stages.

This work developed the following selected rootstocks with potential for entry into longer-term, semi-commercial, trials…

• Navelina: P. trifoliata: Jiangjin large leaf, Small leaf, Ghana and Xianyong
• Lane Late naval: P. trifoliata: Guanyun, Xianyong and Ghana
• Imperial mandarin: C reticulata: Mantou hong and P. trifoliata: Ghana
• Eureka Lemon: P. trifoliata: Wangchang large leaf, No. 22 and Wanyan.

Further evaluation and commercialisation work was carried out through subsequent investments.