Integrated Centre for Drought Research
Department of Crop Physiology, University of Agricultural Sciences, Bengaluru 560 065

Improving the productivity of crops for rainfed environments is the national priority. Even saving the irrigation water without sacrificing the potential yield has phenomenal significance under water limited conditions. Therefore, NAE envisioned taking into cognizance the diverse facets of plant drought stress response and conceptualization of comprehensive program to achieve the goal of improving crop adaptation to stress.

The basic and strategic research of our centre over the years clearly demonstrated that key to crop stress adaptation is in identifying relevant stress adaptive traits, subsequently identify candidate genes and superior alleles and bring them together by adapting diverse molecular tools. Such an integrated approach is being implemented in the center to realize crop improvement for drought tolerance.

Some of the success stories of the center include;

Subprogram 1: Genotypes with constituent drought adaptive traits

Germplasm characterization to identify donor lines with relevant drought adaptive traits

Accurate phenotyping for assessing the variability in desirable traits in a large number of germplasm and breeding lines is the most important prerequisite for identifying suitable trait donor lines for crop improvement.  Several strategies and techniques for precise phenotyping were developed and standardized. 

a. For WUE:  Carbon isotope discrimination and gravimetry.
b. For transpiration rate:  Oxygen isotope enrichment and gravimetry.
c. Root traits:  Root structures and oxygen isotope enrichment.
d. Cellular level tolerance:  Temperature induction response technique
e.Other physiological screens:  Oxidative stress damage, membrane
    permeability, cell viability etc.

Following traits have been characterized in crops like 

Crops Traits characterized
Finger millet Root
Rice WUE, Root and Intrinsic tolerance
Groundnut WUE and Root
sunflower WUE and Root

Sub-program 2: Genes for improving drought tolerance

Transcriptional profiling and activation tagging to identify relevant candidate genes

For improving the drought tolerance of crops through transgenic approach, prerequisite is availability of validated candidate genes. There are now convincing evidence indicate that stress responsive genes are ubiquitously present both in tolerant and susceptible species, however genes present in stress tolerant plants are structurally and functionally more efficient in imparting stress tolerance. Finger millet is one of the stress adapted species and hence prospecting candidate stress tolerant genes has relevance.
With this hypothesis a systematic approach was adapted to identify candidate genes from finger millet. Stress transcriptome of finger millet was developed and evaluated to clone relevant transcription factors as candidate genes. The approach involved development of subtractive stress cDNA library of cloning and validation of stress specific transcription factors by expression analysis down regulation and over expression studies. With this conceptual approach a few stress specific transcription factors were cloned (EcNAC1, EcMYC, EcNAM, EcGBF, EcbZIP, EcZinc-Finger) from finger millet. Functional validation was done by RNAi approach. Transgenics developed in model system tobacco expressing EcNAC, ECNAM were tolerant to water deficit and salinity stress. Some of the stress specific finger millet transcription factors can be potential candidate genes to improve stress tolerance in other crops.
Subprogram 3: Transgenics for improving the drought tolerance

Development of transgenics expressing stress genes and their evaluation

  • Tissue culture-independent in planta transformation protocol developed in groundnut, sunflower and rice.
  • Groundnut transgenics with improved adaptation and productivity under stress have been developed. By adapting transgenic approach, a few relevant drought adaptive traits have been pyramided to achieve field level tolerance with increased productivity. 

This conceptual approach involved initially identification of validated regulatory genes which brings about cellular level tolerance. Similarly, a genotype with superior water relations (water mining and WUE) was obtained by extensive phenotyping the advanced breeding lines. The transformation protocol standardized in the identified genotype provided options to generate large number of events which are extensively screened for stress response using diverse physiological and empirical screens. Some of the promising transgenics expressing upstream regulatory genes like helicases, DREBs were tolerant to stress and also productive. A co-ordinated effort with inputs from 3 sub-programs led to the development of superior transgenics. Regulatory approvals are being obtained for filed evaluation trials.

Subprogram 4:  Trait introgression to improve drought tolerance through molecular breeding

a)Identification of QTL for specific drought traits
b)Development of double haploid as a tool to 
i) Introgress traits
ii) Develop mapping populations

Development of a panel of germplasm amenable for association mapping

Drought tolerance is a highly complex phenomenon and a large number of diverse traits contribute for the comprehensive improvement in drought tolerance.  Hence, developing trait specific mapping populations for identifying QTLs is quite cumbersome.  Association analysis using a panel of diverse germplasm significantly overcomes this limitation.  This strategy depends on the allelic diversity in a set of germplasm accessions, which should represent most of the molecular diversity available for that crop.  A large set of germplasm accessions of rice were genotyped and a panel of 200 accessions have been identified with minimal genetic admixture and population structure.  This population is extensively being genotyped and phenotyped for drought tolerance traits to identify markers in LD with relevant traits.
The most promising feature of association analysis is the possibility of assessing the phenotypic variation by diverse groups.  The panel can be utilized for LD mapping for other traits depending upon the phenotypic variation in the traits of interest.

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