A competitive ELISA for detecting resistance to latent stem infection by Diaporthe toxica in narrow-leafed lupins

Resistance to Diaporthe toxica in 12 lines of narrow-leafed lupin (Lupinus angustifolius) was assessed by a competitive enzyme-linked immunosorbent as say (ELISA). Seedlings were inoculated with the pathogen and after 21 days resistance was assessed by counting latent infection structures in epiderma l tissue under the microscope. Infected stem pieces were then incubated for 6 days in moist chambers before treatment with antisera to D. toxica. Ther e was a high correlation between the ELISA reaction and the frequency of la tent infection structures on the 12 lines (r = 0.92, P<0.001). Visual confi rmation of the ELISA result was obtained by further incubating the excised stems for up to 12 days and assessing the degree of fungal development. The re was a high correlation between the ELISA result after 6 days incubation and visual ratings of fungal development after 12 days incubation (r = 0.89 , P<0.001). The ELISA test distinguished susceptible, resistant and very re sistant lines, but failed to distinguish the intermediate line from resista nt lines. A similar result was obtained with visual observation of fungal d evelopment on excised stems, with the exception that the intermediate line was not distinguishable from susceptible lines. The most accurate assessmen t of resistance was by microscope observation of latent infection structure s, which allowed quantitative assessment of resistance and consistently sep arated susceptible, intermediate, resistant and highly resistant lines.