TOP CROSS AND SINGLE CROSS

1. TOP CROSS AND SINGLE CROSS
ATHIRA RAJAN
athirarajanmt@gmail.com

2. TOPCROSS
• Davis suggested these method in 1927
• In varying designs has played a major role in breeding of
maizes in USA
• Inbred × variety cross (Jenkins 1934)
• Selected plants are crossed with common testers of known
performance,generally in open pollination
• Purpose of using top is to increase the chance of obtaining a
desirable gene

3. • Top cross covers different forms of crosses between mother individuals
and a common polinator
• Only single cross F1s are utilized
• The yield purpose of these crossess is evaluated in replicated trails
on multi locations
• The line which produces high yielding single cross with tester are
selected
• The design has two short falls
✓ First, a single tester variety may not offer wide genetic background
✓ Secondly the number of crosses become large

4. SINGLE CROSS
• Crossing between two inbreds or varieties is called single cross
• Such crosses express maximum amount of heterosis
• Used to measure the specific combining ability of the inbreds
• The selected line are crossed in all possible combination
• They are evaluated in replicated trials over several locations for
yield performance
• These method can evaluate only limited number of inbreds at a
time

5. • Total number of single crosses by a given number of inbreds
(n) can be calculated by the formula n(n-1) and excluding
reciprocals by n(n-1)/2.
• For commercial production of single crosses, a male sterile
line is used as female, the male parent is the restorer line,
the seed set in the female parent is the hybrid seed, but the
seeds of male parent are selfed seed

6. THANK YOU