Improved Rootstocks for Imperial Mandarin Industry Impact: Proven Track Record

Improved rootstocks for Imperial mandarin Industry impact: proven track record

Prior to 2000…… Troyer and Cleopatra

Benton for Imperial 2003, Sunstate Experiment

Barkley for Imperial 2017, Bakers Experiment 13-years-old

Troyer: Benching & tree decline Cleopatra: Phytophthora challenge Troyer 1960s Benton 2003 Barkley 2017

Joint field-day: 7th March 2017, Gayndah

Organised by: QRAC, Citrus Australia Ltd Queensland Citrus Improvement Scheme Inc. Dept of Agriculture & Fisheries Queensland RSVP 3rd March (this Friday) “Growing to market requirements”

What’s that got do with rootstocks?

Funding: Voluntary Contribution project

CT13004 Queensland Citrus Improvement Scheme: finding better rootstocks for Australia. 1. Gayndah ‘Imperial’ rootstock experiment

2. CTV replication and movement in advanced rootstocks

3. Emerald ‘Imperial’ rootstock experiment

4. Breeding new P.trifoliata hybrids with CTV resistance

5. The commercial value of “Extreme hybrids” as rootstocks Laboratory and Nursery Trials: Citrus Tristeza Virus inoculation and screening: >2,500 hybrids Phytophthora screening: >1,500 hybrids

Field Trials: Tegege, Sunstate, 1998: 10 rootstocks→Benton Wallaville, McClennan 2000: 28 rootstocks Gayndah, Bakers, 2004: 33 rootstocks→Barkley Emerald, Presslers, 2011: 66 rootstocks Gayndah, Shepherds, 2013: 245 rootstocks Wallaville, Spencer Ranch, 2016: 138 rootstocks Mundubbera/Gayndah, MHP, 2016/17: 14 rootstocks

Why use Imperial scions?.....good ‘canary’ Rootstock objective: better fruit quality Rootstock objective: better fruit quality

But… Rootstock requirements for Australian conditions

Essential: tolerance to CTV resistance to phytophthora root and collar rot good horticultural performance

Desirable: salt tolerance lime tolerance resistance to nematodes tolerance to waterlogging control of tree size

Minor importance: tolerance to exocortis drought tolerance cold tolerance seedy and nucellar embryony

Australian National Citrus Rootstock Screening Working Party, 1985 Breeding for CTV resistance

Infected bud onto each hybrid Hybrid bud onto infected rootstock Better method, faster results

>800 hybrids completely resistant to CTV, carrying the resistance gene from Poncirus. New challenge…rootstock hybrids with 2 copies of the resistance gene → rapid field deployment.

Breeding for phytophthora resistance

Old Method

Cheaper New Method Faster Cleaner Breeding for salt tolerance Breeding for granulation resistance

Use field trials to identify potential parents (with low granulation) Hybridise these parents Cull for CTV, phytophthora, salt Assess for granulation Unproven method Rootstock requirements for Australian conditions

Essential: tolerance to CTV resistance to phytophthora root and collar rot good horticultural performance

Desirable: salt tolerance lime tolerance resistance to nematodes tolerance to waterlogging control of tree size

Minor importance: tolerance to exocortis drought tolerance cold tolerance seedy and nucellar embryony

Australian National Citrus Rootstock Screening Working Party, 1985 Rootstock requirements for Australian conditions

Essential: tolerance to CTV resistance to phytophthora root and collar rot good horticultural performance HLB tolerance

Desirable: salt tolerance lime tolerance resistance to nematodes tolerance to waterlogging control of tree size warm climate productivity

Minor importance: tolerance to exocortis drought tolerance cold tolerance seedy and nucellar embryony gall wasp

Breeding for new challenges

Choose the right parents (e.g. pumelo, Eremocitrus, Microcitrus for HLB tolerance) Maximise genetic diversity Build breeding populations that have the ‘right stuff’ and dump the rest

e.g. K15 x 14Q055 • 556 hybrid seedlings • 88% fail phytophthora screening •  66 hybrids remaining – 71% fail CTV screening –  19 hybrids remaining • ??% fail salt screening •  perhaps ~10 hybrids for field rootstock testing

~98% of hybrids dumped within 2 years of sowing, and prior to field planting. Minimum cost and effort.

Emerald Imperial Rootstock Trial

• Planted August 2011 • 65 different rootstocks, 891 data trees • Detailed assessments 2014, 2015, 2016

• Major impacts on canopy size, productivity, quality

• Emergence of winners and losers

N639 X639 H639 Nelspruit

Don’t use it! Wallaville Imperial Rootstock Trial

Planted November 2016

605 trees

138 rootstocks (screened for CTV and phytophthora resistance prior to planting)

Genetic diversity Hybrids containing: Poncirus, Swinglea, Clymenia, Atalantia, Fortunella, Severinia, Citropsis, Hesperathusa, Citrus australasica, C.garrawayi, C.glauca, C.junos, C.wintersii, C.reticulata, C.maxima, C.aurantium.

The most genetically diverse rootstock experiment ever planted

Thankyou

• Funding: DAF Qld, Hort Innovation, Qld Citrus Improvement Scheme • Staff: Deb Gultzow, Toni Newman • Field-trial hosts: Bakers, Benhams, Berthelsens, Emmertons, Presslers, Shepherds, Spencer, Trotts. • Professional input and supplies: Andrew Miles and other private researchers/consultants. Helen Hofman, Graeme Sanderson, Nerida Donovan, Mark Skewes, Matt Weinert, Yu Pei Tan and other Agency colleagues. Pat Barkley, Andrew Harty and other industry professionals. John Owen-Turner and Committee Members QCIS. Tim Herrman and the AusCitrus Board • National/ International collaboration and germplasm: NSW DPI, Uni of California, Riverside, CREA Italy, IAC New Caledonia, Jeju Uni South Korea, Uni of Florida Lake Alfred, USDA Fort Pierce, USDA Riverside, Thankyou

Australian citrus growers/nurseries/consultants: for wanting better rootstocks!