Plant Breeding

PLANT BREEDING

 

  • Traditional farming has limitations in biomass production for both humans and animals. Plant breeding emerges as a transformative technology to substantially increase yields and address food scarcity. 
  • Plant breeding plays a pivotal role in achieving remarkable increases in agricultural productivity, as exemplified by the Green Revolution in India. 
  • The Green Revolution not only fulfilled national food requirements but also positioned India as a food exporter, illustrating the success of plant breeding in developing high-yielding and disease-resistant crop varieties. 
  • Plant breeding is the deliberate manipulation of plant species with the goal of creating improved plant types that are well-suited for cultivation, provide enhanced yields, and exhibit disease resistance. 
  • Conventional plant breeding, practiced for millennia, dates back to the beginning of human civilization. Recorded evidence of plant breeding extends 9,000-11,000 years. 
  • Many present-day crops result from ancient domestication practices, and major food crops today are derived from domesticated varieties. 
  • Classical plant breeding involves crossing or hybridization of pure lines, coupled with artificial selection to generate plants with desirable traits such as higher yield, improved nutrition, and disease resistance. 
  • With advancements in genetics, molecular biology, and tissue culture, contemporary plant breeding increasingly incorporates molecular genetic tools. 
  • Primary traits incorporated by breeders include increased crop yield and improved quality. 
  • Tolerance to environmental stresses (salinity, extreme temperatures, drought), resistance to pathogens (viruses, fungi, bacteria), and increased resistance to insect pests are also key focus areas. 
  • Plant breeding stands as a transformative force, contributing to increased agricultural yields, improved crop quality, and resilience to environmental challenges. 
  • The integration of molecular genetic tools signifies a new era in plant breeding, promising continued advancements in agricultural productivity.

 

Systematic Plant Breeding Programs: Key steps in breeding a new genetic variety of a crop- 

  • Collection of Variability:

- Genetic variability is essential for any breeding program. Pre-existing genetic variability is often found in wild relatives of the crop.

- Collection, preservation, and evaluation of diverse wild varieties, species, and relatives of cultivated species are crucial.

- The entire collection, encompassing all diverse alleles for all genes in a given crop, is termed germplasm collection. 

  • Evaluation and Selection of Parents:

- Germplasm undergoes evaluation to identify plants with desirable character combinations.

- Selected plants are multiplied and utilized in hybridization.

- Purelines are established wherever desirable and feasible. 

  • Cross Hybridization Among Selected Parents:

- Desired characters often need to be combined from two different plants.

- Cross hybridization involves collecting pollen grains from the male parent and placing them on the stigma of the chosen female parent.

- The process is time-consuming, and only a small proportion of crosses result in the desired combination. 

  • Selection and Testing of Superior Recombinants:

- Superior recombinants are selected from the progeny of hybrids, showcasing the desired character combination.

- The selection process is scientifically rigorous, aiming to yield plants superior to both parents.

- Selected plants undergo self-pollination for several generations to achieve uniformity (homozygosity). 

  • Testing, Release, and Commercialization of New Cultivars:

- Newly selected lines are evaluated for yield, quality, disease resistance, etc., in research fields under ideal conditions.

- Evaluation extends to farmers' fields across various agroclimatic zones for at least three growing seasons.

- Comparison is made to the best local crop cultivar (check or reference cultivar) to assess performance. 

  • Conclusion of Breeding Program:

- Successful lines that demonstrate superior traits are identified for further development.

- The finalized cultivars undergo commercialization and release for widespread cultivation. 

  • Continuous Monitoring and Improvement:

- Post-commercialization, ongoing monitoring helps assess cultivar performance under diverse conditions.

- Continuous improvement and adaptation of breeding strategies contribute to sustained advancements. 

  • Agriculture and the Green Revolution in India- 
  • India, primarily an agricultural country, contributes approximately 33% to the GDP and employs nearly 62% of the population. 
  • After independence, a critical challenge was meeting the increasing food demand of the growing population. 
  • With limited cultivable land, the focus was on increasing yields per unit area from existing farmland. 
  • In the mid-1960s, the development of high-yielding varieties of wheat and rice through plant breeding techniques led to a significant increase in food production, known as the Green Revolution. 
  • From 1960 to 2000, wheat production surged from 11 million tonnes to 75 million tonnes, and rice production increased from 35 million tonnes to 89.5 million tonnes. 
  • Semi-dwarf varieties of wheat and rice played a crucial role in this surge. 
  • Nobel laureate Norman E. Borlaug, based at the International Centre for Wheat and Maize Improvement in Mexico, developed semi-dwarf wheat. 
  • High-yielding and disease-resistant varieties like Sonalika and Kalyan Sona were introduced in the wheat-growing belt of India. 
  • Semi-dwarf rice varieties, derived from IR-8 (developed at IRRI, Philippines) and Taichung Native-1 (from Taiwan), were introduced in 1966. 
  • Later, India developed better-yielding semi-dwarf rice varieties like Jaya and Ratna. 
  • Crossbreeding Saccharum barberi from north India with Saccharum officinarum from south India resulted in sugar cane varieties with high yield, thick stems, and increased sugar content suitable for north Indian regions. 
  • Successful hybrid breeding in India led to the development of high-yielding varieties of maize, jowar, and bajra, resistant to water stress.

 

Plant Breeding for Disease Resistance

 

  • Fungal, bacterial, and viral pathogens significantly impact crop yields, leading to losses ranging from 20-30% to complete crop failure, especially in tropical climates. 
  • Breeding disease-resistant cultivars is crucial for enhancing food production and reducing dependence on pesticides.
  • Host plant resistance, determined by the genetic constitution, prevents pathogens from causing diseases. 
  • Before breeding, knowledge about the causative organisms and their transmission modes is essential. 
  • Examples of diseases caused by fungi include brown rust of wheat, red rot of sugarcane, and late blight of potato. 
  • Bacterial diseases include black rot of crucifers, and viral diseases include tobacco mosaic and turnip mosaic. 
  • Conventional breeding techniques (hybridization and selection) and mutation breeding are employed for developing disease-resistant varieties. 
  • Steps include screening germplasm, hybridization of selected parents, selection and evaluation of hybrids, and testing and release of new varieties. 
  • Conventional breeding is constrained by a limited number of identified disease resistance genes in various crop varieties. 
  • Inducing mutations artificially through chemicals or radiation (e.g., gamma radiations) allows the creation of new traits. 
  • Mutation breeding is a process where desirable mutant plants are selected and used in breeding. 
  •  Other methods include selection amongst somaclonal variants and genetic engineering to introduce disease resistance genes. 
  • Resistance genes from wild relatives with low yield can be introduced into high-yielding cultivated varieties. 
  • Sexual hybridization between the target and source plants followed by selection achieves the transfer of resistance genes. 
  • Resistance to yellow mosaic virus and powdery mildew induced by mutations in mung beans. 
  • Transfer of resistance genes from a wild species to bhindi (Abelmoschus esculentus), resulting in the new variety Parbhani kranti. 
  • Plant breeding for disease resistance employs diverse strategies, from conventional hybridization to mutation breeding and genetic engineering, aiming to develop resilient crop varieties.

 

 

 

Plant Breeding for Developing Resistance to Insect Pest

 

  • Insect and pest infestations cause extensive damage to crop plants and their produce, emphasizing the need for developing insect-resistant crops. 
  • Insect resistance in host crop plants can result from morphological, biochemical, or physiological characteristics. 
  • Morphological features like hairy leaves in cotton and solid stems in wheat contribute to resistance against specific insect pests (e.g., jassids and stem sawfly). 
  • Non-preference by stem sawfly in wheat with solid stems. 
  • Smooth-leaved and nectar-less cotton varieties that do not attract bollworms. 
  • Maize with high aspartic acid, low nitrogen, and sugar content exhibits resistance to maize stem borers. 
  • The breeding process for insect pest resistance follows the same steps as for other agronomic traits, including yield or quality. 
  • Steps involve screening germplasm, hybridization of selected parents, selection and evaluation of hybrids, and testing and release of new varieties. 
  • Resistance genes can be sourced from cultivated varieties, germplasm collections of the crop, or wild relatives. 
  • Plant breeding for insect pest resistance employs various strategies, including morphological, biochemical, and physiological traits. 
  • The process involves identifying sources of resistance genes and implementing conventional breeding methods to develop insect-resistant crop varieties.

 

 

 

Plant Breeding for Improved Food Quality

 

  • Over 840 million people worldwide lack adequate food to meet daily nutritional needs. 
  • Three billion people suffer from "hidden hunger," characterized by micronutrient, protein, and vitamin deficiencies. 
  • Limited access to fruits, vegetables, legumes, fish, and meat contributes to hidden hunger. 
  • Diets deficient in essential micronutrients (iron, vitamin A, iodine, zinc) lead to health risks, reduced lifespan, and impaired mental abilities. 
  • Plant breeding plays a crucial role in enhancing food quality by developing crops with improved nutritional content.
  • Breeding programs focus on increasing the nutritional value of crops by elevating essential micronutrient levels. 
  • Development of iron-rich crops addresses deficiencies and contributes to combating anemia, a common health issue. 
  • Breeding efforts target crops enriched with vitamin A to address vision-related health concerns and enhance overall well-being. 
  • Development of iodine-enhanced crop varieties helps combat iodine deficiency disorders, promoting better thyroid function. 
  • Breeding for zinc-fortified crops aims to improve immune function and overall health, addressing zinc deficiencies. 
  • Hidden hunger refers to deficiencies in essential micronutrients that may not manifest as immediate hunger but lead to long-term health issues. 
  • Lack of access to diverse, nutrient-rich foods contributes to hidden hunger, impacting a large global population. 
  • Plant breeding initiatives focusing on improved food quality contribute significantly to addressing hidden hunger and combating micronutrient deficiencies on a global scale.

 

Biofortification

 

  • Biofortification involves breeding crops to increase levels of vitamins, minerals, protein, and healthier fats, contributing to improved public health.   
  •  Breeding programs aim to enhance:

- Protein content and quality.

- Oil content and quality.

- Vitamin content.

- Micronutrient and mineral content. 

  • In 2000, maize hybrids were developed with double the amino acid levels (lysine and tryptophan) compared to existing hybrids. 
  • Wheat variety "Atlas 66" with high protein content has served as a donor to improve cultivated wheat. 
  •  Iron-fortified rice variety developed, containing over five times more iron than commonly consumed varieties. 
  • Indian Agricultural Research Institute (IARI), New Delhi, has released vitamin and mineral-rich vegetable crops:

          - Vitamin A-enriched: carrots, spinach, pumpkin.

- Vitamin C-enriched: bitter gourd, bathua, mustard, tomato.

- Iron and calcium-enriched: spinach and bathua.

- Protein-enriched: broad beans, lablab beans, French beans, garden peas. 

  • Biofortification emerges as a practical strategy to combat malnutrition and improve public health on a large scale. 
  • Biofortification, through targeted breeding efforts, enhances crop nutritional quality, addressing specific nutrient deficiencies and contributing to overall public health improvement.

 

Single Cell Protein(SCP)

 

  • With conventional agriculture facing challenges in meeting escalating food demands, Single Cell Protein (SCP) emerges as an alternative protein source. 
  • The demand for cereals increases as it takes 3-10 kg of grain to produce 1 kg of meat through animal farming. 
  • This phenomenon aligns with the trophic levels in food chains, where energy is lost at each level. The shift to meat diets amplifies the demand for primary producers (grains). 
  • More than 25% of the global population suffers from hunger and malnutrition. 
  • SCP involves the cultivation of microbes, such as Spirulina, on an industrial scale to serve as a rich protein source for both animals and humans. 
  • Microbes are grown on diverse materials like waste water, straw, molasses, animal manure, and sewage, offering a sustainable and protein-rich food alternative.
  • Spirulina and other microbes provide essential nutrients, including proteins, minerals, fats, carbohydrates, and vitamins. 
  • SCP production from diverse materials reduces environmental pollution, showcasing a sustainable approach. 
  • A 250 kg cow produces 200 g of protein daily. 
  • In the same period, 250g of a microorganism like Methylophilus methylotrophus can yield an impressive 25 tonnes of protein due to its rapid biomass production. 
  • The widespread consumption of mushrooms and the thriving mushroom culture industry indicate the potential acceptance of microbes as a food source. 
  • SCP, harnessed through microbial cultivation, stands as a viable solution to address protein deficiencies, environmental concerns, and the growing demand for nutritious food.