Little program relating to energy growth that’ll bear fruit (5,4)
I believe the answer is:
apple tree
'growth that'll bear fruit' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'little program relating to energy' is the wordplay.
'little program' becomes 'applet' (I am not sure about the 'little' bit.).
'relating to' becomes 're' (re can mean with regards to).
'energy' becomes 'e' (physics symbol as in E=mcp).
'applet'+'re'+'e'='APPLE-TREE'
Can you help me to learn more?
(Other definitions for apple tree that I've seen before include "may be source of windfall" , "fruitful growth" , "source of fruit" , "Source of the growth that inspired Newton?" , "fruit producer" .)