(a) Describe the history of plant breeding in India. Write the objectives of plant breeding and methods for creation of…

Plant Breeding and Crop Improvement in India

History of Plant Breeding The history of plant breeding in India is a continuum from indigenous selection to scientific precision. While the Vrikshayurveda (c. 600 BCE) documents ancient horticultural practices and plant health management, it serves as a precursor rather than a formal breeding record. Systematic breeding began with the establishment of the Royal Botanic Garden at Saharanpur in 1817, which focused on ornamental and economic species. The pivotal shift occurred with the founding of the Imperial Agricultural Research Institute (IARI) in 1905, marking the era of scientific crop improvement. Post-independence, the Green Revolution transformed Indian agriculture through the introduction of high-yielding varieties like IR8 rice and Sonalika wheat, coordinated by ICAR. The modern era is defined by molecular breeding, with institutions like NBPGR conserving germplasm and BARC advancing mutation breeding, ensuring a robust pipeline for food security.

Objectives and Methods for Variability The primary objectives of plant breeding are to enhance yield potential, improve nutritional quality, and confer tolerance to biotic stresses (pests, diseases) and abiotic stresses (drought, salinity). Additionally, breeding aims to widen the adaptability of crops to diverse agro-climatic zones. To achieve these goals, variability must be created. Key methods include:

1. Hybridization: Crossing genetically diverse parents to combine desirable traits.
2. Mutation Breeding: Inducing heritable changes using physical (radiation) or chemical mutagens, as practiced at BARC.
3. Polyploidy: Doubling chromosome sets to increase vigor and size.
4. Genetic Engineering: Introducing specific genes for traits like Bt cotton.
5. Somaclonal Variation: Exploiting genetic instability during tissue culture.

Systemic Acquired Resistance (SAR) SAR is an inducible, systemic defense mechanism triggered by a localized infection, providing broad-spectrum resistance against subsequent attacks. The signaling pathway involves the accumulation of salicylic acid (SA), which activates the NPR1 gene. This leads to the expression of Pathogenesis-Related (PR) proteins that inhibit pathogen growth. For instance, in tobacco, a localized TMV infection triggers SAR, protecting the entire plant from secondary TMV or bacterial attacks.

Sources of Disease Resistance Resistance sources are distinct from the type of resistance (vertical/horizontal). Actual sources include:

1. Wild Relatives: E.g., Oryza rufipogon for blast resistance in rice.
2. Landraces: Traditional varieties like Pusa wheat strains resistant to stem rust.
3. Mutants: Spontaneous or induced lines with novel resistance genes.
4. Transgenic Lines: Plants engineered with resistance genes from unrelated species.

Advantages of Breeding for Resistance Breeding for disease resistance offers significant advantages: it reduces the dependency on chemical pesticides, thereby lowering production costs and minimizing environmental pollution. It ensures durability when multiple resistance genes are pyramided, and it is a cost-effective, long-term solution compared to repeated chemical applications.

Graft Incompatibility Graft incompatibility is the failure of a scion and rootstock to form a functional vascular union, despite technical success in the grafting procedure. Symptoms:

• Immediate: Necrosis at the graft union, overgrowth of callus tissue, or failure of the scion to bud.
• Delayed: The graft initially succeeds but fails after a few seasons due to vascular discontinuity, leading to premature death or reduced vigor.
• Physiological: Chlorosis, stunted growth, or abnormal fruiting.

Causes:

1. Genetic Incongruity: Incompatibility genes in the rootstock or scion.
2. Biochemical Barriers: Differences in hormone levels or metabolic pathways.
3. Viral Transmission: Pathogens moving from rootstock to scion.
4. Tissue Differences: Mismatch in cambial alignment or cell wall composition.

Examples:

• Citrus: Sweet orange scions on trifoliate orange rootstocks often show delayed incompatibility.
• Pome Fruits: Pear scions on quince rootstocks may exhibit overgrowth.
• Mango: Certain rootstock-scion combinations at IIHR show reduced longevity due to vascular incompatibility.

Conclusion Effective crop improvement in India requires an integrated approach. By combining traditional knowledge with modern tools like SAR exploitation and precise grafting techniques, India can develop resilient, high-yielding crop varieties. Institutions like IARI, NBPGR, and IIHR must continue to collaborate, leveraging germplasm resources to address emerging challenges in climate change and disease pressure.