RA 00048.pdf - OAR@ICRISAT

and regional bases, and t h e a s s e s s m e n t of
c r o p losses in the 1980s.
2.4 Strlga
2.4.1 Present research efforts to develop effective
s y s t e m s of Striga control and t h e
i m p l e m e n t a t i o n of control measures are
totally inadequate for t h e current task. We
r e c o m m e n d that donor agencies set up a
small advisory g r o u p t o s t u d y t h e p r o b l e m
a n d to prepare proposals for a greatly
increased research effort on Striga.
2.4.2 A l t h o u g h s o m e progress has been m a d e in
t h e identification of resistant cultivars, there
is a n e e d to develop s i m p l e and reliable
field-screening techniques, and to understand
t h e various resistance m e c h a n i s m s .
2.4.3 O t h e r aspects requiring attention include:
t h e m e c h a n i s m b y w h i c h nitrogen and
drought stress influence Striga attack, particularly
in t h e m o r e resistant varieties;
better understanding of t h e pattern of
Striga seed germination under field conditions
and t h e reasons for reduced e m e r g ­
ence under w e t a n d / o r shaded conditions;
t h e potential for biological control; t h e
p o t e n t i a l f o r a r t i f i c i a l s t i m u l a t i o n b y
e t h y l e n e and synthetic s t i m u l a n t s ; t h e
potential for induction of resistance by s e e d
hardening w i t h phenolic acids; techniques
for direct a s s e s s m e n t of yield loss (as a
m e a n s of assessing p e r f o r m a n c e of resistant
lines and of generating crop loss data).
2.5 Birds
2.5.1 W e r e c o m m e n d t o donor agencies that
t h e y should continue t o support and e n ­
c o u r a g e (a) research into t h e biology,
m o v e m e n t s , a n d control of Quelea and
other bird p e s t s in Africa, and (b) t h e
transfer of t h e technology to g o v e r n m e n t
organizations t h r o u g h t h e training of plant
protection personnel to take advantage of
t h e progress achieved in recent years.
Similar programs should be initiated w h e r e
birds also severely d a m a g e s o r g h u m a n d
millet grain.
2.5.2 In m o s t situations in Africa, control of
Quelea t h r o u g h a p r o g r a m of total population
reduction is e x t r e m e l y unlikely to succ
e e d because of t h e high reproductive
potential of t h e species and t h e vast inaccessible
areas in w h i c h t h e birds are
distributed and because Quelea, like all t h e
major bird pests, are highly visible migrants
and opportunistic feeders. For practical,
e c o n o m i c a l , logical, a n d e n v i r o n m e n t a l
reasons, w e r e c o m m e n d and support t h e
p r e m i s e that lethal c o n t r o l s h o u l d be
directed only to those birds actually causing
d a m a g e o r w h o s e m o v e m e n t patterns w i l l
take t h e m into susceptible cropping areas.
2.5.3 W e r e c o m m e n d that additional strategies
such as chemical repellents, barriers, cultural
and agronomic m e t h o d s , and genetic
deterrent characteristics in t h e plant itself
continue to be evaluated so that safe,
economical, and effective control techniq
u e s are available for use in appropriate
situations, either alone or in combination
w i t h lethal measures.
3. Genetic Resources
3.1 The task of g e r m p l a s m resources units in
t h e 1980s is enormous. During t h e 1970s a
w o r k i n g collection of s o r g h u m g e r m p l a s m
w a s assembled f r o m across t h e range o f
Sorghum bicolor (L.) M o e n c h . Collections
w e r e classified and m e t h o d s w e r e devised
to maintain these sources. D e m a n d s during
t h e 1980s are going to be for t h e m o r e
efficient use of the a s s e m b l e d g e r m p l a s m .
N e w sources of resistance to diseases and
pests w e r e identified in landraces, and
other collections proved to be of s u c h
superior quality that they w e r e directly
incorporated into breeding projects in c o u n ­
tries far beyond their origins.
3.2 Quality of g e r m p l a s m has b e c o m e m o r e
important than t h e n u m b e r of collections in
g e n e banks. Collecting remains an important
task of genetic resources units. But
collecting efforts m u s t be concentrated in
t h o s e areas w h e r e landraces are in danger
of extinction, and in habitats w h e r e g e n o t y ­
pes of particular value to breeders are
e x p e c t e d t o b e f o u n d . The n u m b e r o f
collections, and range of variation of t h e
close w i l d and w e e d y relatives o f s o r g h u m
also n e e d to be increased. W i l d species
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