Wheat Technical


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Introduction

India ranks second, next to China, in global wheat production, but experts point out that it has the potential to become the largest wheat producer in the world towards the year 2020. During the pre-Green Revolution era, from 1947-65, India had already established a strong wheat improvement programme and several improved tall varieties possessing better yield, superior grain quality and rust resistance were developed. During the Green Revolution era, the introduction of Mexican semi-dwarfs, soon followed by locally bred semi-dwarfs which were released in increasing numbers year after year, and development and adoption of management technologies coupled with desired market and price support, resulted in dramatic increases in yield and total production. Newer semi-dwarfs have continued to increase yield potential by about 0.8 to 1% annually in irrigated areas. Yield losses to diseases, especially rust, were also reduced due to the development of resistant varieties which incorporated new sources of resistance against new races of the pathogens. Moreover, the photo-nonsensitivity of the modern varieties had permitted diversification and intensification of wheat-based cropping systems.

The wheat revolution had generally bypassed the rainfed areas. Acreage under rainfed wheat has been declining and is currently about 25% of the total wheat area and the yields are not only about one-third of that in the irrigated areas but have also been increasing only slowly. The rice-wheat system is showing signs of fatigue and the growth of factor productivity has decelerated. Pressure is also mounting due to the increasing virulence of pathogens, genetic vulnerability and demand for improved grain and product quality. In order to meet these challenges and to secure an evergreen wheat revolution, interdisciplinary research for integrated management of production resources, genetic resource conservation and enhancement, pests and pathogen management, and quality improvement should receive high priority. Development of more efficient and lodging-resistant plant types, hybrid wheat, multiple and horizontal resistance and new crop raising practices, such as ridge-furrow planting, should be emphasized. Molecular breeding and production of transgenics hold great promise for not only diversifying the genetic base but also for enhancing the breeding materials, especially for quality traits and resistance or tolerance to biotic and abiotic stresses.

 
Variety and Crop Improvement

The choice of the correct variety plays a very important role in achieving optimum yield. For deciding on a variety for cultivation under irrigated conditions, the following are very important considerations:

  1. Disease resistance
  2. Fertilizer responsiveness
  3. Lodging and shattering resistance and
  4. Desired maturity

Under rain-fed conditions, the ability to withstand soil and atmospheric drought is most needed. If the right variety is not present, production technologies cannot be applied effectively. The Indian Council of Agricultural Research has released the following seven wheat varieties for different wheat growing zones and production conditions.

Latest Wheat Varieties Released for Various Production Conditions 1999-2000

Variety

Area of Recommendation

Production Condition

Average Yield (Tonnes / ha)

Other Salient Features

Central Release

Shresth

(HD 2687)

Punjab, Haryana, western Uttar Pradesh and parts of Rajasthan

Irrigated, timely sown, high fertility

5.01

Resistance against brown rust race 77-5 and adult plant resistance

UP 2425

Punjab, Haryana, western Uttar Pradesh and parts of Rajasthan

Irrigated, late sown

3.81

Malviya Wheat 468 (HUW 468)

Eastern Uttar Pradesh, Bihar, West Bengal, Assam, Orissa

Irrigated, timely sown, high fertility

4.26

Malav Shakti (HI 8498)

Madhya Pradesh, Gujarat, Southern Uttar Pradesh parts of Rajasthan

Irrigated, timely sown, high fertility

4.52

Durum variety having Sr 2 and Sr 11 genes against stem rust

State Release

UP 2384

Plains of Uttar Pradesh

Irrigated, timely sown, high fertility

4.88

Having Yr 9 resistance gene

Abha

(HI 1454)

Madhya Pradesh

Irrigated, late sown

4.20

Resistant to leaf rust and stem rust

* Experimental name, if different from the cultivar name, is given in the parenthesis


A programme on the incorporation of resistance genes for leaf rust (Lr9, Lr 19, Lr 24) in the background of popular varieties (WH 542, HD 2329, UP 2338 and CPAN 3004) yielded a number of desirable genotypes RRW 3 and RRW 4, showing immunity against leaf rust and resistance to stripe rust, high yield levels and phenotypic characteristics of WH 542. The florets of the chemical hybridizing agents-based male sterile wheat open twice to facilitate cross fertilization. First opening is for a shorter period and second after a gap of 1-2 days is longer (5-6 days). Chemical hybridizing agent in a late-sown crop was more effective than in normal sown wheat.

Wheat Genotypes Resistant to Biotic Stresses 1999- 2000

Three rusts (stem, leaf and stripe) RAJ 3702, UP 2352, HPW 82, DL 547-2, HW 1081 AND HW 1084
Leaf and stripe rust PAF 82/90 and DUCK SEL/TREE LDS x YAV SEL
Three rusts and Karnal bunt RAJ 1555, CMH 82 A 1350, HD 2590, HS 318 and NI 8859
Three rusts, Karnal bunt, leaf blight and powdery mildew H 567-71 DAR
Head scab DLRRL 34 AND KAL-BB x TOFN > S = AUFN
Flag Smut HD 2618, DWR 202 and HD 2636

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.