Xylem, phloem and transpiration flows in developing European plums

Area of Science:

• Plant Physiology
• Fruit Development
• Horticultural Science

Background:

• Neck shrivel is a quality issue in European plum (Prunus × domestica L.).
• Xylem sap backflow from fruit to tree has been hypothesized as a cause of neck shrivel.

Purpose of the Study:

• To quantify xylem, phloem, and transpiration flow rates in developing plum fruit.
• To investigate the role of sap flow dynamics in plum fruit quality disorders.

Main Methods:

• Utilized linear variable displacement transducers to measure fruit volume changes.
• Employed steam-girdling of fruit pedicels to selectively interrupt phloem transport.
• Compared flow rates in control, steam-girdled, and detached fruit.

Main Results:

• Xylem flow rates were occasionally negative (backflow) in the early morning.
• Phloem flow was significant during the day but ceased at night.
• Xylem and transpiration rates correlated with atmospheric vapor pressure deficit during stage II.
• Xylem inflow contributed 79% to total sap inflow in stage II, decreasing to 25% in stage III.
• Phloem inflow contributed 21% in stage II, increasing to 75% in stage III.

Conclusions:

• Xylem backflow occurs in plum fruit but at rates too low to significantly cause neck shrivel.
• Phloem sap flow plays an increasingly important role in plum fruit development, especially in later stages.