The crosses were made between watermelon cold sensitive cultivar (Giza21)
and cold tolerant inbreed line (PIPP8-261). Individual plant data from six generations
(P"P2,F"F2,BC"BC2) were subjected to an analysis of generation means to study the
genetic behavior for the vegetative, yield and fruit traits under winter conditions at
open field. Heterosis of the F, over mid-parent was significant f or a II studied traits
except mature leaf area. The value of potence ratio exceeds one for number of fruits I
plant and total yield I plant, but it was less than one for fruit weight and total soluble
solids content. Broad sense heritability was low for number of fruits I plant and total
soluble solids; and high for fruit weight ar.d total yield I plant. The low temperature -
tolerance in winter was to controlled by a single dominant gene, which could be used
for the development of new cold - tolerance varieties and F, hybrids, thus providing
economic gain due to earlier planting in the open field.