Characterization of ethylene-induced organ abscission in F1 breeding lines of miniature roses (Rosa hybrida L.)

Miniature potted roses are sensitive to ethylene and respond to it by bud and leaf abscission, leaf yellowing and/or flower senescence. The goal of this study was to develop a selection strategy for characterization of ethylene sensitivity in rose breeding lines. Two hundred and thirty-three F1 genotypes were obtained from a reciprocal crossing of ‘Lavender’ and ‘Vanilla’ cultivars, and evaluated in response to ethylene treatment. Based on ethylene-induced organ abscission, low- and high-sensitive genotypes were selected for physiological and molecular studies compared with the parent plants. After 1 week of ethylene treatment, leaf chroma values and chlorophyll degradation were increased in high-sensitive genotypes, much more than in low-sensitive genotypes. However, after 2 weeks of ethylene treatment, low-sensitive genotypes showed no difference in chroma values, but chlorophyll contents decreased in two out of three genotypes. Expression of ethylene receptor genes (RhETR1/3) and signal transduction genes (RhCTR1/2) was not correlated with ethylene sensitivity of the investigated genotypes. The relative expression of laccase (RhLAC) was evaluated with respect to the relationships of lignin deposition and abscission. Ethylene-induced expression of RhLAC in high-sensitive genotypes increased more strongly than in low-sensitive genotypes. The lowest level of RhLAC transcript was accumulated in pedicels of genotypes that showed the lowest bud abscission. Enhanced expression of the laccase gene by ethylene may be related to the abscission process.