Tree Performance, Yield, and Fruit Quality of ‘Valencia’ Sweet Orange (Citrus sinensis L. Osbeck) Selections on New Poncirus trifoliata Rootstocks

This study reports the performance of seven Valencia (Citrus sinensis) selections grafted to four Trifoliata (Poncirus trifoliata) rootstocks in the Riverina region of south-east Australia. Six of the Valencia selections (numbered as Valencia 1 to 6) were from orchards in the Riverina region, and the seventh was a standard commercial variety ‘Keenan’ (control). Three of the four Trifoliata rootstock selections (‘Zao Yang’, ‘Tanghe’, and ‘Donghai’) were imported from the People’s Republic of China, and the fourth was the ‘Tri22’ (control) selection used commercially in Australia. ‘Valencia 5’ produced the highest cumulative (162 kg/tree) yield over the five harvest seasons and increased levels of Total Soluble Solids (TSS, 1.7 °Brix) compared with the current industry standard, ‘Keenan’. Trees grafted to ‘Zao Yang’ produced higher yields than any of the other Trifoliata selections, again outperforming the current industry standard, ‘Tri22’. The new combination of ‘Valencia 5’ scion on ‘Zao Yang’ rootstock represents an opportunity to significantly improve orchard productivity, particularly for juice production. ‘Valencia 6’ on Zao Yang’ had the highest percentage (58%) of fruit >75 mm in diameter compared with other scion/rootstock combinations and creates an additional opportunity for fresh market production. Significant differences in tree size, growth rates, and productivity were identified. Results from this evaluation have resulted in the commercialisation of ‘Valencia 5’ and ‘Valencia 6’ scions and ‘Zao Yang’ rootstock as three new citrus varieties for sweet orange production in Australia.