TOP CROSS AND SINGLE CROSS.pdf

TOP CROSS AND SINGLE CROSS

1. TOP CROSS AND SINGLE CROSS
ATHIRA RAJAN
[email protected]

2. TOPCROSS
•Davis suggested these method in 1927
•In varying designs has played a major role in breeding of
maizesin USA
•Inbred×variety cross (Jenkins 1934)
•Selected plants are crossed with common testers of known
performance,generallyin 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 commonpolinator
•Only single cross F1s are utilized
•The yield purpose of thesecrossessis evaluated in replicatedtrails
onmulti 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 inbredsor 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 inbredsat 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 selfedseed

6. THANK YOU