Resistance to anthracnose is decreased by tissue culture but increased with longer acclimation in the resistant strawberry cultivar

Inoculation of tissue-cultured plants of strawberry cultivar Ichigochukanbohon-Nou2gou (Nou-2) with the anthracnose pathogen (Glomerella cingulata) results in wilting and plant death, whereas inoculation of strawberry runners grown in greenhouses results in leaf spots, not wilting or death. When tissue-cultured Nou-2 plants were acclimated for 3, 9 or 15 days, plant resistance to anthracnose increased as the acclimation period increased, suggesting that the resistance of Nou-2 may be induced by external factors. To clarify the mechanisms of resistance, we used cDNA microarray analyses to compare gene expressions among tissue-cultured and acclimated plants of the resistant cultivar Nou-2 and the susceptible cultivar Tochiotome. As a result, we identified 18 cDNA clones that were upregulated during acclimation in Nou-2 but not in Tochiotome. In a real-time RT-PCR of the 18 clones, the expression levels of three were significantly higher in acclimated plants of Nou-2. Two of the three clones showed close homology to enzymes related to flavonoid biosynthesis, i.e., leucoanthocyanidin dioxygenase (LDOX, ANS) and UDP-glucosyltransferase, putative (3-GT). The clones spotted onto the cDNA microarrays were rechecked, and 23 nonredundant cDNA clones of 13 enzymes were estimated to be flavonoid biosynthetic enzymes. Most of these clones were upregulated by acclimation in Nou-2.