In Vitro Screening of Easter Lily (Lilium Longiflorum Thunb) for Resistance to Stem Rot Caused by Phytophthora Cactorum.

Callus cultures were initiated using 0.5 cm bulb scale segments of Easter lily (Lilium longiflorum Thunb) cultured on a medium designated CI-1, which contained (per liter), 4.3 g Murashige and Skoog basal salts, 30 g sucrose, 8 g agar, 0.4 mg Thiamine, 100 mg myo-inositol, 2.5 mg 1-naphthaleneacetic acid (NAA) and 0.1 mg N-(phenyl-methyl)-1-H-purine-6-amine (BA). Calli derived from 3 cultivars of Easter lily, 'Ace', 'Harson' and 'Nellie White', susceptible to the fungus Phytophthora cactorum, were irradiated with UV light (25 erg mm$\sp{-2}$ s$\sp{-1}$) for 0-28 days at 4 day intervals. The calli were then subcultured for 4 weeks on CI-1 medium containing different concentrations of the fungal-culture filtrates. From a total of 34560 calli, six filtrate-resistant-variants (FRV) were isolated and challenged with the fungus. Results did not suggest that UV treatments enhanced the frequency of resistant calli. About 21% of the calli obtained from FRV calli were resistant to the fungus after callus increase. Plants were regenerated from calli by placing on CI-1 minus growth regulators. Regenerated plants were planted in vitro on 10-day-old fungal cultures, and evaluated after 3 weeks. Eighty percent of the tested plants exhibited resistance and were established in pots. Electrolyte leakage from susceptible and resistant callus tissues was measured after 4 h exposure to culture filtrates. A small, gradual increase in conductance was observed in resistant tissues, before reaching a plateau; however, for susceptible tissues conductance continued to increase throughout the 6-h test period. Calli not exposed to filtrate manifested no change in conductance.