Comparing callus growth with discoloration and electrical conductivity as measures of stem injury after freezing woody plants

摘要

Most of 36 crabapple and 19 other woody plant taxa demonstrated the ability, when dormant, to grow a continuous row of callus along the cambial region on split-stem pieces within 5 to 7 days of incubation at 25deg C. Callus growth was then compared todiscoloration and electrical conductivity as measures of injury after freezing stem pieces of Jack crabapple (Malus baccata cv. Jacki), pink bud Sargent crabapple (M. sargentii [M. toringo] cv. Rosea), Mary Potter crabapple (Malus sp. cv. Mary Potter), and snowberry mountain ash (Sorbus discolor cv. Maxim). Sampling dates for laboratory freezing tests were chosen to represent midwinter cold hardiness and partial hardiness of either late autumn or early spring. There was a high correlation between discoloration and callus ratings for most plants. However, the critical temperature (T50) for injury identified by callus growth was often 3-6deg C lower than for discoloration. For many taxa, callus growth was easier to identify than discoloration of cambium andphloem. TTC (2,3,5-triphenyl tetrazolium chloride) treatment was sometimes useful to identify growth of callus that died after forming. The critical temperature (Tc), the highest temperature at which relative electrical conductivity differed significantly from the control temperature, was higher in most cases than the T50 for callus and discoloration, indicating less cold hardiness. It is concluded that the callus procedure may have value for evaluating injury to the cambial zone from freezing and other plant stresses because it determines the ability of the plant to continue growth.