Analyses of early rough bark phenotype found in seedlings of a cross between the European pear 'Bartlett' and the Chinese pear 'Yali'

One of the morphological symptoms of old age in trees is the development of rough bark on trunks and branches. Here we characterized pear seedlings with a unique phenotype, early rough bark (ERB). Eight-year-old normal and ERB seedlings from a cross between the European pear (Pyrus communis) cultivar 'Bartlett' and the Chinese pear (Pyrus bretschneideri) cultivar 'Yali' were used for morphological analyses and the determination of carbohydrates and lignin. Many rough surface patches were observed on the stems of 2-year-old ERB shoots, and most stem surfaces were covered by rough bark in 3-year-old ERB shoots while most stem surfaces were smooth in 2- and 3-year-old normal shoots. ERB plants also displayed rough-barked trunks, and the trunk surface was relatively smooth in normal plants. The content of lignin, one of the major components of cork tissues, was higher in ERB plants than in normal plants. The levels of starch and sucrose, which play roles in storage and translocation of carbon, were higher in ERB plants than that in normal plants, suggesting that the rate of carbon use is low in ERB plants. The novel phenotype ERB may enable future research on the formation of rough bark in fruit trees.