Proceedings of the Fifth Asian Regional Maize Workshop - Search ...

achieved.
It has adequately been shown that in the presence of opaque-2 the lysine and tryptophan
content is nearly doubled. This increase in the level of these two amino acids results in the
aarked increase in the biological value. In spite of this nutritional superiority, the lack of
extensive acceptability of the opaque-2 varieties is due to their soft chalky endosperm, the
opposite of the vitreous endosperm types of the flint to semiflint maize varieties. The opaque-2
varieties have a similar problem to those associated with the soft kernel type, which face
difficulties for safe storage since they are more prone to weevil attack when stored at lower
elevations. Considerable variation in kernel vitreousity exists within a opaque-2 broad based
populations and it was, therefore, thought appropriate to improve the frequency of hard endosperm
(HE) types.
Intensive work in this direction was started in 1971, with the release of three opaQue-2
composite varieties. Selection approaches adopted were: individual kernel selection, ear-to-row
selection, and reciprocal full-sib selection. Among the three selection approaches, more
promising results were obtained with reciprocal full-sib selection, primarily because of the
presence of reciprocal/maternal effects. A broad based hard endosperm opaque-2 composite, SO/SN
has been developed. In terms of yield and frequency of HE the Indian cultivars are comparable
with HE materials developed at CIJ+1YT, Mexico. Realizing the popularity of sweet and pop corns
in the country, attention has also been laid for the development of their improved cultivars.
Two cultivars, Madhuri and Madhu Makka in the sweet corn group, and Amber pop and VL-Amber pop in
popcorn group have been released so far.
To date, more than five dozen hybrids and composites have been released for COIlI1l8rcial
cultivation with either yellow or white grain color, flint to semiflint texture, early to late
maturity range, and adaptation for irrigated and also for rainfed conditions. Also, these
cultivars posses a fairly good level of tolerance/resistance to important diseases and pests.
Develos-'lt of .ize cultivars suitable for various fal"llling systems.
The cultivars released prior to 1971 belonged to the full season maturity group. In 1974
a program to develop materials of medium and early maturity was initiated with the result that we
have today improved cultivars belonging to various maturity groups, thereby farmers have a wide
option to choose a maize cUltivar to fit in their cropping system (Table 3).
Synthesis of broad-based pools for the devel~t of varieties.
A few broad based pools representing various maturity groups and grain color were developed
to cater to needs of various agro-ecological regions of the country. Mobilization of
desirable progenies selected from these pools yielded promising varieties. After the proper
evaluation and selection, the promising materials were used to synthesize composites or varieties.
The following five broad based pools mobilizing the available elite materials were
fonmulated: pool AB-yellow, AB-white, Be-yellow, CD-yellow, CD-white, representing three maturity
groups and two grain types. After initial synthesis, each of these pools has undergone six
cycles of random mating. The individual pool was grown in a half-sib nursery and the 1-2 most
promising ears in nearly ~ of the elite progenies were retained and tested at 4-6 locations
during summer season. The seed from selected ears was grown during the winter season in a halfsib
recombination block to random mate the population and develop progenies for next cycle.
Again, from this nursery 1-2 best ears from each of the progenies were retained for next cycle
(second cycle of half-sib selection). selected elite half-sibs were used to synthesize an
improved version of the population.
Gain through intrapopulation illlProvement seleCtion.
The intrapopulation improvement program at the national level was initiated in 1974 using
ten elite composite varieties representing different maturity groups. A full-sib family selection
scheme with two levels of selection intensity was used. under this selection program about
250 full-sib progenies were evaluated at 4-6 locations for grain yield and other agronomic
characters. In addition, these progenies were also evaluated for one or more important
disease(s) and insect pests under artificial inoculations and infestations. After harvest, based
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