RA 00015.pdf - OAR@ICRISAT

A mold-resistant composite is being developed
to increase levels of mold resistance and to
improve grain quality in an agronomically good
background through recurrent selection procedures.
Currently, male sterility is being incorporated
into selected entries.
Mold resistance is being incorporated into
advanced populations and an attempt is being
made to evaluate the effect of extra-long freethreshing
papery straw-colored glumes as barriers
to grain mold organisms.
A program initiated to develop cultivars suitable
for the postrainy season - incorporating
lines with 90 to 105 days maturity, excellent grain
quality, substantial fodder value, resistance to
shoot fly, and tolerance to drought - has reached
the F 2 stage. Seed from 500 crosses is available
for evaluation in postrainy season 1977. Yields
of some of the photoinsensitive lines tested in the
rainy and postrainy seasons 1976 are presented
in Table 5.
Attempts to recover sorghum in a plump grain
with high lysine content are frustrated by instability
in the lysine concentration - with a
reversion to lower (normal) lysine levels. Work
towards a better understanding of the reasons for
this is part of a Ph.D. thesis study now under way
at ICRISAT Center.
Across the breeding program, selection for
locally desirable grain quality-i.e., bold, reasonably
hard, pearly white seed - is practiced. A
program to attempt to evaluate breeding stocks
for food characteristics is being initiated.
Breeding for Striga Resistance
Screening sorghum in the laboratory to identify
plants with low or no strigol production is now
under way. So far, 3053 cultivars have been
screened and 115 were found to have low stimulant
production. Some of these have at least
partial resistance to shoot fly, midge, grain mold,
and other yield reducers, thus enhancing their
value to the breeding program. Performance of
the top 15 cultivars is compared to that of checks
in Table 6. Difficulty in uniform field screening
led to large coefficients of variation.
Striga asiatica and S. densiflora are found in
India, while S. hermonthica is found primarily in
Savannah Africa. Five Nigerian lines with resistance
to S. hermonthica were also found to be
low-stimulant types for S. asiatica. Preliminary
data were obtained suggesting that many of the
lines which are low-stimulant types for S. asiatica
were positive for 5. densiflora; however there did
not appear to be much difference in reaction to S.
asiatica seed collected from several sites in India
(Table 7). These data are being checked.
It is now well established that some sorghum
cultivars, though strigol positive, have resistance
which operates after Striga seed has attempted to
parasitize them. In cooperation with the
ICRISAT cereal physiology group, studies of the
mode of attachment - using root sections of
susceptible and resistant genotypes - have been
made. The mechanism of resistance appears to be
associated with thick-walled endodermal cells
and the presence of silica crystals in these cells
(see Sorghum Physiology, page 35).
Our field-screening studies at Akola and
ICRISAT Center showed that 15 of the 275
entries tested had high levels of resistance (Table
6). These will be incorporated into agronomically
elite material.
Inheritance studies indicate that low strigol
production is controlled by a single recessive
gene. Further studies on the nature of inheritance
of other resistance mechanisms will be
undertaken with material currently being
assembled.
Breeding for Pest Resistance
This program was initiated with the objective of
strengthening resistance to the three major pest
groups present in the SAT—stem borer, shoot
fly, and midge. Available resistance is being
incorporated into desirable plant types with
good yield and quality traits; populations are
being bred to combine higher levels of resistance
with agronomically good plants. Resistances
found in Indian and African sources were intercrossed,
using male sterility, for a second time
in the rainy season; progeny of these crosses will
be further evaluated. Selections following crossing,
backcrossing, and double crossing have been
31