Abstract：Taking watermelon variety‘Zaojia 84-24’ as scion and pumpkin variety‘Zhenzhuang’
as rootstock，this paper studied the effects of different scion or rootstock age on growth and development
of watermelon seedlings grafted by machine．The results showed that the ages of scion and rootstock would
significantly affect the quality and root regeneration of grafted seedlings．Besides，the main factor affecting
the survival rate，lateral root number，root length and root volume of grafted seedling，etc. was the age of
rootstock seedling．And the main factor affecting the leaf health index was the age of scion seedling．While，
the absolute growth rate of the new leaves was jointly affected by the ages of rootstock and scion seedlings，
but there was no significant correlation．The age of rootstock seedling suitable for mechanized amplexiform
determined by comprehensive evaluation of satisfaction was 16 days，namely：the size of first real-leaf being
a coin size，stem diameter being 3.20 ± 0.16 mm．The age of scion seedling was 16-19 days，namely： from
first true-leaf appeared to one leaf and one-core period，and stem diameter being 2.76 ± 0.23 mm．
