HLB Tolerance – Scions and Rootstocks M. L. Roose Botany and Plant Sciences University of California, Riverside [email protected] October 2019 Slide source: Ed Stover Varieties with HLB Resistance and Tolerance

Other sources of tolerance • Many citron hybrids including rough lemon • Some pummelos • Some mandarins

Slides from Chandrika Ramadugu, UCR From Ed Stover Non-Citron Background Robinson

Konejime sour orange hyb

Egami Buntan pummelo C. maxima

Pineapple Sweet Orange Scarlet Emperor mandarin From Ed Stover Volkamer Lemon Hybrid Diamante citron

S Coast Field Station Citron

Santa Barbara Rangpur

From Ed Stover Florida Rootstock Trial

Swingle 812 C146 Swingle C146 US897 C22 US897 C35

Kuh C35 C22 C57 Swingle C57 C35 US897 Not many HLB symptoms so far Data from W. Castle Marsh Grapefruit Trial in Florida Data from W. Castle X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X C54 C22 C146

2007 planting, 2014 rating Vernia orange rootstock trial in Basinger FL

C54 X X639 US812 X US802 X CLEO SWIN KUH C57 C22 US896 US897 Healthy

Sick

Castle et al, 2015 Tolerant Rootstocks from Florida? • USDA (Kim Bowman) – source of US802, US942 etc. A large program with a national mission • Many rootstock selections recently released • Some do not produce nucellar seeds – micropropagation • Most are at CCPP • U Florida (Jude Grosser, Fred Gmitter, Bill Castle) • Do not have a national mission (except through USDA grants) • A few rootstocks released, many candidates in pipeline • Could decide to sell patented rootstocks to individual companies in California • A few older selections tested in California • Rootstocks and scions at CCPP (USDA-MAC project) Exploiting Natural Resistance and Tolerance • Conventional breeding – possible, but a long road if Eremocitrus or Microcitrus is the source or resistance • Need rapid generation time - plants expressing a gene that regulates flowering are being developed • Identify gene and why it causes resistance • Mapping and genomics experiments for resistance • Poncirus – Gmitter, Stover and Roose • Eremocitrus – Ramadugu and Roose, Stover • Mapping experiments for tolerance • Fortune x Fairchild - Roose and Stover • Sugar Belle – Gmitter • Citrons - Stover • Transfer gene to sweet orange, edit sweet orange gene, introduce gene with viral vector …