Abstract: We investigated the suitability of micro-variation of stem diameter as an indicator for fruit diameter growth during fruit development period. The micro-variations of stem diameter during fruit development period of peach and pomegranate trees were monitored at Yunnan Province. We analyzed the changes in maximum daily diameter shrinkage (MDS) and maximum daily stem diameter (MXSD), as well as their responses to meteorological factors and soil water. The relationships between stem diameter growth parameters and fruit daily growth in fruit diameter (FDG) were studied. Results showed that MXSD and minimum daily stem diameter (MNSD) of the two fruit trees occurred at specific times. MDS and MXSD of both fruit trees were sensitive to meteorological factors (r²≥0.50, P<0.001). There was a positive linear relationship between MXSD and soil water for both fruit trees (r²=0.65 and 0.45, P <0.001). The MDS of peach tree was negatively affected by soil water (r²=0.39, P<0.001), whereas such pattern was not detected in pomegranate tree. The significant relationship between stem daily growth (SDG) and FDG of both fruit trees calculated based on MXSD (r²=0.48 and 0.38, P<0.001) indicated a lag effect of environmental stress on FDG relative to that on SDG. With respect to SDG and its relationship with FDG, -0.005 mm·d^-1 for peach and -0.063 mm·d^-1 for pomegranate was established as a threshold value. Below such value, FDG could decrease under environmental stress. The daily increment of MDS in both trees had no relationship with FDG. Our findings suggested that MXSD is an appropriate indicator for fruit expansion stage of both peach and pomegranate trees, and that the effect of environmental stress on fruit diameter growth can be monitored by temporal change of MXSD during fruit development period.

Key words: fruit development period, stem diameter, meteorological factor, soil water, fruit diameter growth