The last 50 years have witnessed unprecedented growth in production,
productivity and scientific activity of wheat. The decade ending 1975
witnessed a burst in wheat production and productivity, which, in conjunction
with similar breakthroughs in rice, was termed as Green Revolution.
This marked a new era in agricultural research and development, in which
modern principles of genetics, plant breeding, agronomy, plant pathology
and social sciences were judiciously applied to develop appropriate
technologies. In view of the trends of production and research, the
post-independence period can be divided in 3 eras: Pre-Green Revolution
era, from 1947 to the mid-sixties, is characterized by wheat of traditional
tall types which were non-responsive to intensive management, but generally
possessed good grain quality, especially for chapati-making.
The Green Revolution era, from the mid-sixties to the seventies, is
distinguished by the introduction and exploitation of semi-dwarf wheat,
which were responsive to intensive management and provided the much-needed
breakthrough in productivity and production. The Post-Green Revolution
period is characterized with the consolidation of the gains of the Green
Revolution, breaking of the yield barriers, and preparation for the
next wheat revolution. In the pre-Green Revolution phases, Indian scientists
directed their efforts at increasing productivity, physical appearance
of the grain and chapati- making quality. During the Green Revolution,
attention was diverted also to other quality traits of Indian wheats
and as a first step protein content and gluten strength were recorded.
Chapati-making properties were further improved and parameters
of the same standardized. In recent years, data on baking strength,
development area and mixing time, stability of dough development, resistance
and extensibility were collected keeping in view the end product. On
the basis of above information, Indian wheat flours may be divided into
3 groups, viz. strong, medium-strong and weak. Strong gluten varieties
were found to be most suitable for bread and for expression of high
loaf volume, attractive brownish crust, silky and small granular structure
of crumbs. Popular varieties such as HI 977, NI 5439, HW 657 and DWR
39 possessed this kind of gluten. Medium-strong gluten made excellent
chapatis. It allowed good dough consistency, soft and viable
with high puffing and keeping quality. Varieties like Sujata, Mukta,
Lok 1, WH 291, UP 2338, WL 711, WH 542, HP 1209, C 306, HD 2402, HD
2189, HW 147, HI 1077, Kundan and Raj 3077 belonged to this group. Weak
gluten varieties suited most for biscuits and cookies. Sonalika, HD
2285, HD 2278, K 8027, HD 2501, DC 784-3 and PBW 175 belonged to this
class.
High Yielding Varieties
With the creation of high genetic potential for yield in the new wheat
varieties, the problem of stability of wheat production assumed greater
significance. Kalyansona and Sonalika, which became widely popular following
the introduction of semi-dwarf genotypes in India, at one stage, occupied
most of the irrigated area under wheat. Indian scientists recognized
the possible dangers of genetic uniformity of this kind and took steps
to diversify the genetic base of varieties to prevent disease epidemics,
because instability in production earlier was mostly due to rust epidemics.
Pathologists kept a close watch on the pattern of rust movement by disease
survey. In 1971-72 when new biotypes of leaf and stripe rusts were observed
on widely grown Kalyansona, pathologists warned that the new biotype
might create serious disease problems in the main wheat belt of India.
Before the disease completely took over Kalyansona, breeders were ready
with genetically different alternative varieties. Nearly 170 varieties,
using Indian x exotic germplasm in most cases, were released. Several
of these varieties were adopted in other countries and have significantly
contributed to their wheat productions. With the release of new genotypes
combining greater resistance to rusts and other diseases and larger
per day production, the yield potentials were continuously improved.
As a result, average yield of the entire Ludhiana district in Punjab
in 1995 was about 5 tonnes/ha. Areas in the intensive production tracts
such as in Punjab and Haryana have already achieved an average yield
of 4.5-5.0 tonnes/ha. There is a technology transfer gap in such areas
and a kind of stagnation in productivity gains is being witnessed. Over
the years, Kalyansona followed by WL 711, HD 2329, UP 2338 and PBW 3430
show linear increases in yield potentials of wheat varieties. The genotypes
emerging from spring x winter crosses have been particularly high yielding.
Current varieties involving the CIMMYT material like Parula, Attila
and Weaver are certainly high yielding but possess low test weight.
Efforts should be made to increase their 1,000-grain weight without
compromising with grain number and the ideotype. In producing still
high yielding genotypes it will be necessary to synergistically combine
the various desirable physiological and yield traits. In the past there
has been limited interaction between physiologists and plant breeders
and this situation needs to be corrected and the 2 groups of scientists
should work in a highly interactive manner. Unlike in rice, heterosis
has not been exploited in wheat improvement. Focused attention should
be given to hybrid wheat. This will also call for inter-disciplinary
research involving breeders, agronomists, physiologists and agro chemists.
A good number of male gametocides are already available in the market.
The IARI has also developed a new male gametocide, which is under trial.
A few selected centres in the country should be strengthened to undertake
the 3 – and 2- line hybrid programmes in wheat. The IARI has already
taken lead in this direction and some of the male-sterile lines along
with their restorers have been distributed to other co-operating centres
in the country. But, the effort needs further consolidation and a network
on hybrid wheat should be established. The scientists at IARI have also
developed a variety DL 802-3, which has outstanding resistance to rust
and gives higher yield than HD 2285 and `Sonalika’ in north-western
plains (average yield 4.1 tonne and maximum yield 5.7 tonnes/hectares).
Developing Disease and Resistent Varieties
Since dwarf wheat varieties expressed their full yield potential under
conditions of high inputs of fertilizers and irrigation, a large-scale
cultivation of the dwarfs could change the microclimate of the area,
which would be favourable to the fungal diseases. Recognizing this fact.
Indian scientists spearheaded the National Wheat Disease Survey and
Surveillance Scheme in 1967. Through this scheme wheat diseases were
sought to be monitored with the help of mobile survey and trap nurseries
planted at strategic locations. This kind of survey and surveillance
helped to detect the build up of leaf rust and stripe rust on vastly
cultivated Kalyansona in 1970-71 in North-western India, localized epidemic
of stem rust in Sanchore (Rajasthan) on Kharchia local, leaf rust build-up
on Sonalika in Uttar Pradesh and Bihar in 1980, Karnal bunt epidemic
on Arjun in 1974-75 and sporadic occurrence of other wheat diseases.
But for the monitoring through survey and surveillance, the disease
build-ups would have gone unnoticed and the country would have been
caught napping. Regular monitoring and warnings by pathologists kept
the breeders on heels and they were ready with alternative varieties
before it was too late. Another important advantage from this survey
was a precise information on epidemiology of rusts and their migration
path in India. This information enabled Indian scientists to develop
management strategies of rusts. Besides, information on performance
of high-yielding varieties was an additional outcome.
Fighting the rust Deployment of rust-resistant wheats/genes:
This strategy aimed at erecting gene barriers against the spread
of rust from the areas of great vulnerability. This strategy led to
the development and release of a number of varieties with high degree
of resistance in different parts of country. Some of such varieties
were Arjun (SD 2009), Nilgiri (HD 2135), HD 2189, HD 2204, HD 2285,
Girija, Shailaja, HW 517, HP 1102, HP 1209, Lok 1, WH 147, K 7410, HUW
206, HUW 234, WH 283, WH 291, WH 542, UP 2338 and PBW 343 among T.
aestivum; and HD 4502, HD 4530, RAJ 911, RAJ 1555, PBW 34 and DWL.
Fighting rust at its base:
Disease survey, surveillance and epidemiological studies by Indian scientists
showed that leaf rust survives in the northern hills and establishes
itself in the foothills of Himalayas from where it further migrates
to the plains. Similarly, stripe rust is introduced from the northern
hills to the plains. Similarly, stripe rust is introduced from the northern
hills to the plains; stripe rust remains confined to the cooler regions
in the northern plains. This rust also survives in Nilgiri and Pulney
hills of south India but does not spread to the plains due to high temperatures.
Stem rust mainly migrates from Nilgiri and Pulney hills to the plains
and moves northwards. Leaf rust, however, also survives in Nilgiri and
Pulney hills and moves northwards from there. These studies laid the
foundation of a well-thought strategy to nip the problem of rusts in
the bud itself. Towards this strategy, genetic barriers were erected
in the northern and southern hills. Wheat varieties Nilgiri (HD 2135)
and Girija which were found to be highly resistant at these foci of
infection were identified and released from Nilgiri and lower hills
of Himalayas respectively. With the help of State Departments of Agriculture,
these 2 varieties were saturated in these hills. This strategy proved
successful. The wheat crop remained remarkably free from serious rust
attacks for decades to come.
Development of multilines:
Efforts have also been made in the past to develop multilines to minimize
losses due to rusts. Two multilines, MLKS 11 and KSML 3, have been released
for the irrigated areas of the North-western plain zones. However, several
factors such as organization of precise seed multiplication programme
and development of higher-yielding, rust-resistant varieties through
conventional methods affected their acceptance by farmers.
Gene deployment:
Since the frequency and distribution of various rust virulence varied
considerably in wheat-growing areas, scientists advocated the deployment
of specific resistance genes. Several such plans were proposed which
aimed at cutting down the load of inoculum of the specific races by
growing varieties with specific resistance genes.
Gene postulation:
The procedure for characterization of virulence provided new insight
for identification of virulence gene in the pathogen and postulation
of resistance gene in the host. Thus stem rust resistance genes (Sr
3, Sr 5, Sr 7a, Sr 8, Sr 9b, Sr 9c, Sr 11, Sr 15, Sr 24, Sr 30 and
Sr 31), leaf rust-resistance genes (Lr 14a, Lr 20, Lr 23, Lr
24 and Lr 26) and yellow rust-resistance genes (Yr 2,
Yr 3a and Yr 9) were postulated in a large number of semi-dwarf
varieties.
Multilocational disease testing:
Multilocational disease testing of wheat germplasm was initiated in
different areas to use the multiple resistance against all the important
wheat pathogens. This kind of testing, which aims at screening against
diseases at hot spots, is an effective instrument of All-India Coordinated
Wheat Improvement Project and provides information on stable field resistance
to important diseases. From this nursery assured disease-resistance
sources are made available to breeders for use as donors in their breeding
programmes. Of late, lines derived from Mexican material under cultivation
in India have been reported to be under attack of Yr 9 virulence
of yellow rust. Pathologists have already sent a warning signal in the
plains of north India. Intensive efforts now are under way to encounter
this threat by using sources resistant to this pathotype. Indian scientists
would be able to face this challenge by giving suitable alternatives,
as they have done in 1970-71 when Kalyansona was attacked. Sources resistant
to Yr 9 pathotype have already been identified and crosses with
such genotypes are under way.
Durable resistance to diseases
The management of various wheat diseases, whose incidence has been increasing,
with the intensification of wheat production, deserves further research
and technology development efforts. Last year, yellow rust because of
the breakdown of Yr9 was already encountered in Jammu and Kashmir,
Punjab, Himachal Pradesh and Haryana. Continuous monitoring of different
rust biotypes, identification of resistance genes (Yr, Lr and
Sr) and convergence of such genes for consolidating adult plant
resistance for comprehensive management of rust is absolutely essential.
Foliar diseases specially caused by Helminthosportium spp are
becoming more serious and are causing considerable damage even in the
North-western plains zone. Centres of excellence for breeding resistant
varieties as well as for management of these diseases should be established
in hot spots. Considering that these diseases are of particular significance
in the North-eastern plain zones, the IARI is establishing an advanced
centre of research on foliar diseases at its centre at Pusa, Bihar.
The work on Karnal bunt done at the IARI has also opened ways for screening
varieties resistant against this disease, but the breeding work has
not been as intensive. Because of the possible restriction posed on
wheat export due to this disease, India should give greater emphasis
on developing genotypes resistant to Karnal bunt. Phalaris minor
continues to be a major weed problem in wheat production. Recent
studies have shown that several biotypes of this weed which are now
showing resistance against commonly used weedicides, have emerged. An
integrated management programme to keep this weed under control, if
not completely eliminated, is essential.
Other diseases
Even as the rust was kept under effective check, other diseases,
notably among them, Karnal bunt appeared prominently. Disease epidemiology
and life-cycle were studied and also chemical measures were tried. Simultaneously,
a search for genetic resistance was made. Though initial attempts were
not successful, several sources of resistance could be located. Donors
like HD 29, HD 30, HD 2281, HD 4564, HD 4566, HI 8073, HW 730, HW 737,
HW 740 and HP 1531 showed considerable degree of resistance. A linear
model has been developed to enable disease prediction essential for
prophylactic treatment. Besides, loose smut, alternaria blight, powdery
mildew and leaf blotch were also investigated for chemical and biological
control. Strategies for integrated disease management were also developed
to withstand disease pressure.
Developing Climatic Tolerance
Improvement in heat tolerance under irrigated and rainfed conditions
There is a need to develop varieties and management practices to alleviate
the depressing effects of heat during germination or maturity or both.
In the irrigated areas of the Indo-Gangetic plains, a lot of wheat is
sown after middle of December. These genotypes mature when the atmospheric
temperature is very high and humid and as a result there is a high incidence
of leaf blight and brown rust as well as forced ripening which reduce
the grain size and the yield. Varieties suitable for such conditions
should be developed, as area under such ecosystems is likely to increase.
These varieties, such as Halna and HD 2402, should be able to germinate
and establish themselves at low temperature, have faster growth rate,
possess resistance to brown rust and foliar diseases, and tolerance
to heat during the dough stage and onwards. Such types are particularly
required in the North-western plain zone. As mentioned earlier, in the
rainfed areas, especially in dryland areas, varieties, which can tolerate
high temperature during germination and can produce adequate biomass
on limited moisture availability and can mature without affecting the
seed quality in fast-receding moisture conditions and increasing temperature
would be ideal. Varieties like HD 2189 which has completely replaced
Kalyansona in the Peninsular zone and is a prominent variety in that
area, should be developed for such tracts where winter is very short,
as in the south of Vindhyas. This will call for greater interaction
among plant physiologists and breeders. Such high-yielding varieties
can play an important role in the states like Maharashtra where yields
up to 4 tonnes/ha can be obtained after sugarcane.
Biotechnology for Wheat Improvement
Although transgenics were reported in wheat as early as 1991, limited
progress has been made in exploiting transgenics. However, molecular
breeding is progressing satisfactorily. Several laboratories in the
world are preparing molecular maps of wheat, and are using RFLP and
RAPD techniques to identify genes for quality and disease resistance.
Such programmes however are in infancy in India and a few laboratories,
such as at IARI, should give greater attention to molecular breeding.
Biotechnology offers great opportunities for altering quality suited
for food and industrial uses. India should become an active partner
in the International Triticeae Mapping Initiative.
Advanced Crop Management
Germplasm conservation and enhancement
India is one of the important centres of diversity of T. aestivum,
T. durum and T. dicoccum wheat. A good number of land races
particularly after the introduction of high-yielding varieties with
the beginning of the Green Revolution were collected and are being conserved
at our National Gene Bank. In the early phase of the Green Revolution,
1966-1970, bulk of the wheat varieties under cultivation was derived
from Indian x exotic crosses. However, in recent years there has been
an increase in the proportion of the Indian x Indian crosses and there
is a commensurate decrease in the exotic x exotic crosses. Several of
the old Indian wheat famous for their distinct attributes has been used
for different purposes such as Hindi 62, Pissi Local and Bijaga Yellow
are excellent sources of heat and drought tolerance. Kharchia Local
is an excellent source of salt tolerance. Likewise, our famous quality
wheat such as NP 4 and K 68 have been used widely in wheat breeding
programmes aimed at quality improvement. Indian emmer wheat possessing
high protein and greater ,1,000-grain weight are valuable genetic resources
which must be protected and further utilized in the breeding programmes.
Recognizing alien wheat species possess useful genes, their conservation
and utilization must assume high significance. Breeding programmes have
successfully transferred rust resistance genes such Yr 8 from
Aegilops squarrosa, Sr 26 from T. elongatum and
Sr 27 from Secale cereale. Selected centres such as the
IARI should intensify and further consolidate their works on tapping
the secondary and tertiary gene pools of wheat for enhancing genetic
potential of cultivated types. Such gene pools will also be extremely
helpful in developing hybrid wheat.
