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POSTERS: Late Breaking II

P-668 - Field Trial of Five Experimental Avocado Rootstocks Shows Promising Resistance to Phytophthora cinnamomi in Hawaii

Tuesday, August 5, 2025
10:15 AM - 11:00 AM HST
Location: Exhibit Hall 3

    Presenting Author(s)

  • LK

    Lukas J. Kambic

    University of Hawaii At Manoa
    Hilo, HI, USA

    • Author(s)

  • SW

    Sharon Wages

    Extension Agent
    University of Hawaii at Manoa
    Hilo, Hawaii, United States

    • Author(s)

  • PM

    Patricia M. Manosalva

    Associate Professor
    University of California, Riverside
    Riverside, California, United States

  • KW

    Koon-Hui Wang

    University of Hawai'i at Mānoa
    Honolulu, Hawaii, United States

  • MT

    Miaoying Tian, PhD

    Distinguished Professor
    University of Georgia
    Tifton, Georgia, United States

  • AA

    Achyut R. Adhikari

    University of Hawaii at Mānoa
    Honolulu, Hawaii, United States

Abstract Text: The University of California Riverside (UCR) rootstock breeding program has selected
five new advanced avocado (Persea americana Mill.) rootstocks (PP35, PP40, PP42,
PP45, PP80) for their resistance to Phytophthora Root Rot (PRR), a major disease
affecting avocados worldwide. Here, we report early results from a Hawaii-based field
trial of these five UCR advanced experimental rootstocks. East Hawaii Island's growing
environment presents high rainfall, naturalized avocado trees and histosolic soils with
widespread presence of Phytophthora cinnamomi, the causal agent of PRR. The UCR
experimental rootstocks and 'Dusa', a moderately PRR resistant commercial
rootstock, were propagated with a modified Frolich technique and grafted with cv.
Sharwil as scion. Additional grafted 'Sharwil'-scion trees with uncharacterized
seedling rootstocks were purchased as representatives of typical Hawaii commercial
nursery genetics. Trees were planted in a 5x10 grid at 7.5m spacing in a former 
cattle pasture with confirmed presence of P. cinnamomi. At 18 months post-planting, 
‘Sharwil’ trees grafted on 'Dusa’ and on local commercial rootstock exhibited higher 
mortality ('Dusa' p=0.0033, local nursery rootstock p=0.026, Fisher’s Exact Test). 
P. cinnamomi was recovered from roots of a subset of symptomatic control trees,
indicating that these trees were colonized by the pathogen. Phenotypic data collection 
regarding field performance, development, and production is currently ongoing.