An inoculation method for evaluating resistance of cacao to Crinipellis perniciosa
1995
Frias, G.A. | Purdy, L.H. | Schmidt, R.A.
Methods are described to collect and store basidiospores of Crinipellis perniciosa and to inoculate seedlings of cacao (Theobroma cacao) for evaluation of resistance to witches'-broom disease. Basidiospores of C. perniciosa collected overnight in a 16% glycerol solution (containing buffer and Tween 20) remained viable but did not germinate until the collecting solution was diluted to 3% glycerol. Basidiospores freshly collected or stored in the collecting solution for 1 week at 4 degrees C, or stored in liquid nitrogen for up to 18 months remained viable and, after application to cacao seedlings, caused witches'-broom. Witches'-broom developed on inoculated susceptible seedlings placed in a dew chamber for 4 to 6 h at 25 degrees C, but did not develop on seedlings after 2 to 4 h of wetness. Maximal percentages of seedlings became diseased with 15 h of wetness. Differences in percentage of witches'-broom were evident among susceptible and putatively resistant cacao families inoculated with basidiospore concentrations of 10,000 and 12,500 spores per ml; however, higher concentrations (25,000 to 100,000 per ml) resulted in nearly 100% disease. Likewise, inoculation of flushes with large succulent leaves resulted in high percentages of disease in all families. Discrimination among families by percentages of diseased seedlings was achieved when small (0.3 to 1.5 cm) leaves were inoculated. Procedures for basidiospore collection and storage, inoculation of cacao seedlings, and control of pre- and postinoculation conditions support the effective and efficient screening of cacao for resistance to witches'-broom disease.
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