Reactions of selected bean germ plasm to infection by Fusarium oxysporum f. sp. phaseoli
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Permanent link to this item: http://hdl.handle.net/10568/44009
A Brazilian isolate of Fusarium oxysporum f. sp. phaseoli (F. o. f. sp. phaseoli) was used to determine the reactions of 66 lines of beans to the Fusarium yellows pathogen in greenhouse tests. The distal 1 cm of root tips of 1-wk-old seedlings grown in sterilized sand were removed, roots were dipped in a spore suspension of F. o. f. sp. phaseoli for 5 min, and the seedlings were then transplanted into pots filled with pasturized soil. As the concentration of F. o. f. sp. phaseoli spores was increased from 0 to 1 × 107 / ml, incubation time to the first disease symptom was decreased and disease severity ratings (DSR) increased on the field-susceptible cultivar IPA 1. However, only slight disease symptoms occurred at a spore concentration of 1 × 107 on the line HF 465-63-1, known to show resistance under field conditions in Brazil. Severely infected plants became defoliated and often died within 2 3 wk. The dead stem and petiole tissues were covered with pink to orange spore masses. The extent and intensity of vascular discoloration was generally proportional to the overall foliar disease severity. Forty bean accessions evaluated with an inoculum concentration of 1 × 106 spores per milliliter were resistant (DSR 1 3), six were intermediate (DSR 3.1 6.0), and 20 were susceptible (DSR 6.1 9.0). Based on these results, an international nursery consisting of 48 entries of bean germ plasm for evaluation against F. o. f. sp. phaseoli has been formulated and is available for distribution from the Centro Internacional de Agricultura Tropical (CIAT).