Disease resistance screening for Koa wilt disease
N. S. Dudley (1), T. Jones (2), R. L. James (3), P. Cannon (4), R. Sneizko (5), I. Rushanaedy (2), D. BORTHAKUR (2)
(1) Hawaii Agriculture Research Center, Kunia, HI, U.S.A.; (2) University of Hawaii at Manoa, Department of Molecular Biosciences & Bioengineering, Honolulu, HI, U.S.A.; (3) U.S. Forest Service, Vancouver, WA, U.S.A.; (4) USDA Forest Service, Pacific Southwest Region, Vallejo, CA, U.S.A.; (5) Dorena Genetic Resource Center, Cottage Grove, OR, U.S.A.
Phytopathology 101:S216

The wilt disease of Acacia koa (koa) due to infection by Fusarium oxysporum f. sp. koae causes high rates of mortality in field plantings and threatens native koa forests in Hawaii. Identifying and developing wilt resistant koa populations may be the key to successful koa reforestation and restoration. The objectives of this research were to screen koa seedlings for resistance and susceptibility to Fusarium wilt and to determine if resistance is correlated with levels of expression of different classes of chitinases. We have isolated complete cDNAs encoding four different classes of chitinases from koa. In greenhouse experiments, seedlings grown from seeds of selected koa trees were screened for resistance and susceptibility using a mixture of virulent F. oxysporum isolates as the inoculant. Koa families with relatively high frequencies of resistant progenies were grouped as ‘resistant’ while families with high frequencies of seedling mortality were grouped as ‘susceptible’. We are now testing the half-sib progenies from resistant and susceptible families for expression levels of the chitinase genes using quantitative PCR. Expression levels of the chitinase genes may provide an additional measure of wilt resistance of the koa seedlings that survive infection by virulent isolates of F. oxysporum.

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