Differential Flooding Tolerance of Some Dwarfing Pear Rootstock Clones Selected from the Progenies of Pyrus betulaefolia and P. calleryana

Abstract

Response and tolerance to flooding of potted open-pollinated seedlings, four ungrafted dwarfing clonal selections of Pyrus betulaefolia Bunge (PB), six of P. calleryana Decne (PC), and the same topworked to the Japanese pear ‘Kosui’ were investigated. The 3-yr-old trees were flooded for 15 days or 12 weeks and then examined for tree survival, growth cessation, shoot growth, adventitious root formation, and defoliation. Although the tolerance to water stress was higher in PC than in PB, the responses varied within and between the species. Some SPRB clones with greater tolerance than the PC control and SPRC clones developed adventitious roots on the trunk above the water surface. This may be a morphological adaptation to the stress. Prolonged flooding separated the rootstocks into 4 overall rankings: most tolerant (SPRB22), very tolerant (SPRB13, SPRB15, PC1, PC2, SPRC15, and SPRC20), moderately tolerant (SPRC3 and SPRC8) and least tolerant (PB seedling, PB4, SPRB1, SPRC5, and SPRC13). PC and its selection flooded for 30 days had significantly higher shoot growth, new roots, and higher 2,3,5-triphenyltetrazolium chloride (TTC) reducing activity in the fine roots than the PB ones. Within the SPRB clones, SPRB15 and SPRB22 exhibited the most shoot and new root growth. From the analyses of long and short-term flooding data, we categorized the selections SPRB15, SPRB22, SPRC15, and SPRC20 that developed adventitious roots with extended root activity as having superior ability to withstand water stress.