Graduate Thesis Or Dissertation

 

Assays to determine tolerance of cherry rootstock to bacterial canker caused by Pseudomonas syringae pv. syringae Público Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2n49t5163

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  • Bacterial canker, caused by Pseudomonas syringae pv. syringae is recognized as one of the greatest limiting factors in cherry production in Oregon. Disease incidence may be decreased when susceptible cultivars are high-grafted onto tolerant/resistant rootstocks. This research was begun to develop a rapid screening method which could be used to test cherry rootstocks for tolerance to Pseudomonas syringae pv. syringae. In 1988, one-year-old wood of 'Napoleon', 'Corum' and F/12-1 was collected at monthly intervals from November until January. 'Napoleon' and 'Corum' are found to be susceptible, and F/12-1 to be tolerant to Pseudomonas syringae pv. syringae. Twigs were inoculated with water, one avirulent, and three virulent strains of bacteria at 10⁵, 10⁶, and 10⁷ cfu/ml. Browning, gummosis, and callus production were evaluated at the inoculation site after incubation for 4 weeks. Generally, browning and gummosis induced by concentrations of 10⁶ and 10⁷ cfu/ml across the virulent strains were not different. No gummosis and browning were observed on twigs inoculated with water or the avirulent strain. Callus production did not appear to be a usable criterion of the disease in this assay. 'Napoleon' and 'Corum' had significantly higher browning and gummosis ratings than F/12-1. In 1989, one-year-old twigs from 'Napoleon', 'Corum', and a number of cherry rootstocks were collected from October until December . The rootstocks included: F/12-1, M x M 2, M x M 39, M x M 60, GI 148-1, GI 148-8, GI 154-2, GI 154-5, GI 169-15, GI 172-9, and GI 173-9. Twigs were inoculated with water alone as a check, one avirulent and three virulent strains at 10⁷ cfu/ml. Incision browning, gummosis and callus production were evaluated after incubation for 4 weeks. Based on incision browning and gummosis all the rootstocks tested were more tolerant than 'Napoleon' and 'Corum', and most did not differ from F/12-1. However, rootstocks GI 172-9 and GI 169-15 showed more browning than F/12-1 in a number of instances. On the last sampling date, rootstocks M x M 2, GI 173-9, GI 148-8, and GI 154-2 showed less browning than F/12-1. The expression of virulence genes in P. syringae has been shown to be induced by plant signals extracted from cherry leaves. Crude aqueous extracts from 'Napoleon', 'Corum', and various cherry rootstock twigs were adjusted to a concentration of 0.2, 1.0, and 2.0 mg-ml⁻¹, and evaluated for the ability to induce virulence in Pseudomonas syringae pv. syringae. A decrease in activity was generally observed at the two highest concentrations of plant extracts. Reduced activity may have been due to inhibition of the assay or saturation of active sites of the enzyme produced by the bacteria. Compared to tolerant genotype F/12-1, 'Napoleon' and 'Corum' had the highest activity of all the genotypes tested. Rootstocks M x M 60, GI 148-1, GI 148-9, GI 154-5, and GI 169-15 had higher activity than F/12-1 in plant extracts of 0.2 mg-ml⁻¹. Activity induced in rootstocks MxM2, MxM39, GI 154-2, GI 172-9, and GI 173-9 was not different from that of F/12-1. The lowest activity observed was for 'Colt', however this activity was not statistically different from that induced by F/12-1.
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