Recently, scientists from the Agharkar Research Institute (ARI), based in Pune, have discovered two alternative dwarfing genes, Rht14 and Rht18. These genes can play a pivotal role in moderating the rice crop residue burning – more commonly known as stubble burning. This independent research institute works under the Department of Science and Technology.
The Stubble Burning Issue
In India, approximately twenty-three million tonnes of remaining rice residues are burned annually by farmers. This action helps to clear the straw and prepare fields for the subsequent wheat crop but results in significant air pollution. Furthermore, dry environments present obstacles for the germination of wheat varieties with short coleoptiles – the sheath protecting the young shoot tip in grass or cereal. Short coleoptiles are typically less suited for deeper sowing conditions, which are often necessary in these arid environments.
Current Wheat Varieties and Their Challenges
The existing semi-dwarf wheat varieties carry the conventional Rht1 dwarfing alleles, first explored during the Green Revolution. The Reduced Height (Rht) genes lower plant height, thereby increasing productive tillers or sprouts. Despite producing good yields under high-fertility irrigated conditions, these varieties falter in dry conditions due to their shorter coleoptiles. The result is often a decrease in seedling emergence due to low early vigor, or slowed plant growth.
Introduction of New Dwarfing Genes
ARI has successfully mapped the dwarfing genes Rht14 and Rht18 on chromosome 6A in a durum variety of wheat. Concurrently, DNA-based markers were developed for better selection of these genes in wheat breeding lines. These markers allow wheat breeders to accurately select wheat lines containing these alternative dwarfing genes, despite a large pool of breeding lines. These genes are correlated with better seedling vigor and longer coleoptiles.
The Benefits of Rht14 and Rht18
It has been demonstrated that the dwarfing genes Rht14 and Rht18 in wheat confer a reduction in plant height similar to the Rht1 alleles. However, these new genes maintain early vigor in wheat seedlings and do not impact the length of the coleoptile and seedling shoot. As such, Rht14 and Rht18 can serve as valuable alternatives to Rht1 for deeper sowing conditions or fields with retained stubble.
Adapting Indian Wheat Varieties
The ARI is currently utilizing DNA-based markers to assist in transferring these genes into Indian wheat variants. This will ideally make these variants more appropriate for sowing in rice stubble-retained conditions and dry environments.
Marker-Assisted Transfer: An Indirect Solution
Marker-assisted transfer is an indirect selection process where a trait of interest is selected based on a marker linked to it. These markers can be morphological, biochemical, or DNA/RNA variation, and relate to traits like productivity, disease resistance, abiotic stress tolerance, and quality.
Reducing Stubble Burning: The Bigger Picture
Embracing wheat lines with these new dwarfing genes can significantly reduce occurrences of stubble burning under the rice-wheat cropping system. This would mean farmers no longer need to resort to stubble burning to prepare their fields for the next crop. Moreover, these lines allow for deeper sowing of wheat seeds, leveraging residual moisture in the soil, saving water resources, and lowering cultivation costs.
Addressing Environmental Impact and Improving Genetic Diversity
Stubble burning detrimentally affects the environment, soil health, and human wellbeing. Therefore, integrating these alternative dwarfing genes into wheat improvement programs is essential. Greater diversification of the genetic base of dwarfing genes is also critical in catering to the diverse wheat-growing zones in India. Lastly, rigorous Research and Development related to gene varieties can significantly enhance crop productivity.
