RA 00048.pdf - OAR@ICRISAT

o n e recessive maturity g e n e a n d t w o o r three
recessive height g e n e s into t h e c h o s e n tropical
varieties. The tropical conversion p r o g r a m has
p r o c e e d e d according to plan w i t h o u t a single
necessary change. Fortunately, t h e project proposal
included t h e provision of returning each
c o n v e r t e d cultivar to its o w n c y t o p l a s m at t h e last
backcross.
I am sure that my interests are t o o n a r r o w for
m e t o have g o o d j u d g m e n t about w h a t you a n d
t h o s e w h o f o l l o w y o u m a y b e d o i n g i n t h e near
and distant f u t u r e . H o w e v e r , I n o w recognize
s o m e of t h e m i s c o n c e p t i o n s that I labored under
for m a n y years a n d think I recognize s o m e
research w o r k that should b e d o n e n o w .
A s D o g g e t t (1970) has s u g g e s t e d , s o r g h u m
probably e v o l v e d in tropical Africa and spread to
t e m p e r a t e zones a n d t o other continents w i t h i n
t h e last 2 0 0 0 years. S o r g h u m has b e e n in t h e
w e s t e r n h e m i s p h e r e for only about 2 0 0 years and
o n l y a v e r y f e w varieties, including t h e q u e s t i o n ­
able relative S. halepense, arrived e v e n t h e n . But
n o w that t h e tropical conversion p r o g r a m has
b e e n under w a y for about 2 0 years, plant breeders
t h r o u g h o u t t h e w o r l d have m a n y o f t h e desirable
varieties f r o m tropical Africa a n d India available to
t h e m . A l s o , if y o u as plant breeders in t h e tropics
are interested in shorter heights, y o u should
realize that tropical " b u l k s " are available f r o m t h e
conversion p r o g r a m that s h o u l d be of interest to
y o u .
S o r g h u m has b e e n a g o o d c r o p to w o r k w i t h as
inheritance in t h e species s e e m s to c o n f o r m to
t h e principles recognized b y Gregor M e n d e l a b o u t
a c e n t u r y ago.
W h e n I visited a graduate course in plant
breeding just b e f o r e I graduated f r o m Texas A & M
College in 1924. I received t h e i m p r e s s i o n that
g e n e s t h a t control g r o w t h w e r e i n n u m e r a b l e and
that any plant included in its hereditary c o m p l e ­
m e n t n u m e r o u s m i n o r metabolic deficiencies.
T h e s e ideas g r e w o u t o f t h e efforts t o explain t h e
g e n e t i c s of hybrid vigor. East a n d J o n e s (1919) in
their t e x t b o o k said that " i t is only necessary to
a s s u m e that in general t h e favorable characters
are i n s o m e d e g r e e d o m i n a n t over t h e unfavorable,
and t h e n o r m a l over t h e a b n o r m a l i n order t o
have a reasonable explanation of t h e increased
d e v e l o p m e n t of hybrids..." Of course, plant horm
o n e s w e r e n o t k n o w n a t t h e t i m e b e c a u s e W e n t
(1928) had not y e t r e p o r t e d t h e recognition of
auxin as a g r o w t h regulator.
In 1937, I w a s coauthor of a paper on hybrid
vigor in s o r g h u m (Karper and Q u i n b y 1937) that
contained g o o d data and s o m e beautiful pictures.
B u t s o m e o f our conclusions b e c a m e a n embarr
a s s m e n t t o m e later because w e had not
recognized that it w a s t h e c o m p l e m e n t a r y action
of a f e w height and m a t u r i t y g e n e s that had
resulted i n m u c h o f t h e a d d e d g r o w t h that w e had
o b s e r v e d and attributed to hybrid vigor.
It finally b e c a m e c o m m o n k n o w l e d g e that
self-pollinated species should not carry n u m e r o u s
metabolic deficiencies a n d as late as 25 years ago
t h e r e w e r e geneticists (Sinnott e t al. 1958) w h o
t h o u g h t that hybrid vigor should not occur in a
self-pollinated species. But that notion had to be
a b a n d o n e d w h e n hybrid vigor w a s s h o w n t o b e
p r e s e n t in self-pollinated species s u c h as sorg
h u m .
Grain s o r g h u m yields did not increase in t h e
U n i t e d States until hybrids appeared but t h e
genetic and physiological basis of hybrid vigor is
still n o t u n d e r s t o o d . A f e w years ago I r e v i e w e d
t h e literature on t h e genetics and physiology of
hybrid vigor (Quinby 1974) and p r e s e n t e d t h e idea
that parents and hybrids differed in h o r m o n e
levels. But h o r m o n e levels in parents and hybrids
have not yet been e x a m i n e d . But t h e idea that
n u m e r o u s g e n e s control plant g r o w t h is still w i t h
us and is part of t h e basis of t h e theories of
population i m p r o v e m e n t .
During t h e t i m e I w a s studying t h e inheritance
of maturity and height (Quinby and Karper 1945
a n d 1954), I d e v e l o p e d m a t u r i t y g e n o t y p e s in
identical genetic backgrounds that differed at
t h r e e maturity g e n e loci and three height g e n e
loci. I finally c o n c l u d e d that t h e g e n e s controlling
t h e t i m e of floral initiation a n d i n t e m o d e elongation
w e r e probably controlling h o r m o n e levels. I
t h e n p r e s e n t e d m y ideas (Quinby 1974), w i t h o u t
proof, hoping that s o m e plant physiologist w o u l d
u s e t h e m a t u r i t y and height g e n o t y p e s t o s t u d y
t h e h o r m o n a l control of. plant g r o w t h .
Dr. P. W. M o r g a n at Texas A & M University a n d
several of his s t u d e n t s have b e e n d e t e r m i n i n g
h o r m o n e levels in m a t u r i t y g e n o t y p e s of M i l o a n d
papers covering that w o r k are beginning to
appear. Gibberellin is n o w k n o w n to h a s t e n floral
initiation in s o r g h u m (Williams a n d M o r g a n , in
press) a n d that auxin levels are higher in tropical
t h a n in t e m p e r a t e M i l o g e n o t y p e s (Dunlap a n d
M o r g a n , in press). It is a s s u m e d that inhibitory
levels of auxin delay floral initiation of tropical
varieties being g r o w n in t e m p e r a t e zones.
In addition. Dr. F. R. Miller a n d I, using solutions
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