In vitro screening of sugarcane to evaluate smut susceptibility

Tissue-cultured plantlets of three sugarcane (Saccharum spp.) cultivars having a known field smut reaction were screened for susceptibility to Ustilago scitaminea H&P Sydow. Plantlets were inoculated with 0.5 mu l of a suspension of equally mixed quantities of plus and minus mating type sporidia of U. scitaminea at concentrations ranging from 1 x 10 super(1) to 1 x 10 super(6) cells. Fungal sori (whips) were produced in cultivar N12 (intermediate) 6 weeks following inoculation with 1 x 10 super(5) mixed sporidia and thereafter in cultivar NCo310 (susceptible) but not in cultivar N19 (resistant). Sori bearing teliospores were produced up to 3 months following inoculation and incubation at 26 degree C. No sori were produced at mixed sporidial concentrations lower than 1 x 10 super(5)cells. The in vitro soral production in cultivars N19, N12 and NCo310 was 0, 27.5 and 47.5% respectively. Plantlets inoculated with 1 x 105sporidia of only one mating-type did not produce sori in any of the three cultivars tested. Blind scoring of an unknown sugarcane cultivar by this method corresponded exactly with its field smut rating.