Alternative Dwarfing Genes in Wheat

• 22 May 2020

Why in News

Recently, scientists at Pune based Agharkar Research Institute (ARI), have mapped two alternative dwarfing genes Rht14 and Rht18 in wheat that can help in reducing rice crop residue burning i.e. stubble burning.

• ARI is an autonomous institute of the Department of Science and Technology.

Background

• In India, close to twenty-three million tonnes of leftover rice residues are annually burnt by farmers to get rid of the straw and prepare their fields for sowing wheat, which is the next crop, resulting in air pollution.
• Also, dry environments pose a challenge for the germination of wheat varieties with short coleoptile.
  
  • Coleoptile is a sheath which protects the young shoot tip in a grass or cereal.
  • Short coleoptiles are generally less adapted for the deeper sowing conditions.
• The presently available semi-dwarf wheat varieties, which were explored during the Green Revolution, carry conventional Rht1 dwarfing alleles.
  
  • Alleles are the variant form of a given gene.
  • The Reduced Height (Rht) genes decreased plant height and increased productive tillers (sprouts).
• The present variety produces optimum yields under high-fertility irrigated conditions.
• However, they are not well adapted for deeper sowing conditions in dry environments due to shorter coleoptiles, and low early vigor (measure of increase in plant growth) often results in reduced seedling emergence.

Key Points

• Alternative Dwarfing Genes:
  
  • ARI mapped the dwarfing genes Rht14 and Rht18 on chromosome 6A in a durum variety of wheat, and DNA-based markers were developed for a better selection of these genes in wheat breeding lines.
    
    • Genetic/DNA marker is any alteration in a sequence of nucleic acids or other genetic traits that can be readily detected and used to identify individuals, populations, or species or to identify genes involved in inherited disease.
  • The DNA-based markers will help wheat breeders to precisely select wheat lines carrying these alternative dwarfing genes from a massive pool of wheat breeding lines. These genes are associated with better seedling vigour and longer coleoptiles.
    
    • Breeding line is a group of genetically identical homozygous individuals that, when intercrossed, produce only offspring that are identical to their parents.
  • It has been found that dwarfing genes Rht14 and Rht18 in wheat conferred a plant height reduction comparable to the Rht1 alleles while retaining early vigour in wheat seedlings, but do not affect coleoptile length and seedling shoot length.
  • Therefore, these can be utilized as an alternative dwarfing genes to Rht1 for deep sowing conditions or in fields with retained stubble.
  • The DNA based markers are being used at the Institute for marker-assisted transfer of these genes in Indian wheat varieties, so as to make them suitable for sowing under rice stubble-retained conditions and dry environments.
    
    • Marker-assisted transfer: It is an indirect selection process where a trait of interest is selected based on a marker (morphological, biochemical or DNA/RNA variation) linked to a trait of interest, e.g. productivity, disease resistance, abiotic stress tolerance, and quality.
• Advantages:
  
  • The wheat lines with these alternative dwarfing genes will help in reducing stubble burning incidences under the rice-wheat cropping system.
  • The improved lines will make it possible for farmers to sow wheat under rice stubble-retained conditions.
    
    • It means farmers won't have to resort to stubble burning for preparing their ground for the sowing of the next crop.
  • These lines will also allow deeper sowing of wheat seeds to avail advantage of residual moisture in the soil, therefore, saving valuable water resources and reducing the cost of cultivation to farmers.

Way Forward

• Burning of leftover rice crop residue (stubble burning) has serious implications for the environment, soil, and human health. Therefore, there is a need to include alternative dwarfing genes in wheat improvement programs.
• Also, only two dwarfing alleles of Rht1 are predominant in Indian wheat varieties; therefore, it is required to diversify the genetic base of dwarfing genes considering diverse wheat growing zones in India.
• Also there is a need for rigorous Research and Development related to the gene varieties of crops so that productivity of the crops can be enhanced.

Source: PIB