The 1918 Silkworm That Still Dyes Mysore Silk a Single Shade

In the silk-producing districts of southern Karnataka, a single shade of yellow has defined luxury for over a hundred years. The golden hue of Mysore silk — neither the cream of Chinese mulberry silk nor the off-white of most Indian varieties — comes from a living archive: a silkworm strain called PM x CSR2, bred continuously at the Mysore Sericulture Station since 1918. No other silkworm, no chemical dye, no post-production treatment can replicate that exact colour. This is the story of how a colonial-era crossbreeding experiment accidentally fixed a colour, and why that colour may be fading.

The Silkworm That Refuses to Mutate

Mysore silk's signature golden-yellow is not applied after weaving; it is present in the raw cocoon itself. The colour is the direct result of a specific silkworm strain, officially designated PM x CSR2. PM stands for Pure Mysore, a local race, and CSR2 for Chinese Silkworm Race 2, a Japanese-developed hybrid. Since 1918, this strain has been reared exclusively at the Mysore Sericulture Station, a research facility under the Karnataka State Sericulture Research and Development Institute.

What makes PM x CSR2 remarkable is its genetic stability. Silkworms, like all domesticated insects, are prone to mutation and crossbreeding. Yet this strain has remained essentially unchanged for over a century. Each generation, breeders cull approximately 5% of worms that show colour variation, ensuring that only the purest golden-yellow cocoons are used for reproduction. The result is a genetic line so pure that it is considered a living heritage — a silkworm that refuses to mutate.

The colour itself is not a dye but a pigment absorbed from the mulberry leaves the worms eat. The PM x CSR2 strain lacks the enzyme that normally breaks down carotenoids — the same compounds that colour carrots and egg yolks. Instead of excreting these pigments, the worms incorporate them into the silk fibroin, locking the golden hue permanently into the thread.

Attempts to produce the same colour by dyeing white silk have failed. The carotenoid pigment in PM x CSR2 silk is chemically bound to the protein structure, not surface-applied. Dyed silk fades with washing and sunlight; PM x CSR2 silk does not. This permanence is why authentic Mysore silk sarees can be passed down for generations without losing their lustre.

How a Colonial-Era Experiment Fixed a Color

The origin of PM x CSR2 lies in a 1918 experiment by British sericulturists at the Mysore Sericulture Station, then part of the princely state of Mysore. The British goal was straightforward: increase silk yield to compete with Chinese and Japanese production. They crossed the local Pure Mysore silkworm — hardy but low-yielding — with the Chinese Silkworm Race 2, a high-yielding Japanese-developed hybrid imported from Japan.

The hybridisation was successful in boosting silk output, but it also produced an unexpected side effect. The offspring spun cocoons of a vivid golden-yellow, far more intense than either parent. The colour was traced to a recessive gene that blocked carotenoid breakdown. Because both parent strains carried the gene (though it was masked in the CSR2 parent by a dominant suppressor), the hybrid expressed it fully.

British sericulturists initially saw the colour as a curiosity, not a feature. But local weavers in Mysore, who had long prized naturally coloured silks, quickly recognised its value. The golden-yellow became associated with Mysore's royal court and, later, with the region's silk saree industry. By the 1920s, the strain was being deliberately maintained for its colour, not just its yield.

The name PM x CSR2 was formalised in the 1950s when the station began systematic breeding records. The strain is technically a single-cross hybrid, meaning it must be recreated each generation by crossing the two parent lines. This requires maintaining both Pure Mysore and CSR2 populations separately — a labour-intensive process that few other sericulture centres have attempted.

The Chemistry Behind the Sheen

The golden colour of PM x CSR2 silk is due to two carotenoids: lutein and β-carotene. These pigments are abundant in the mulberry leaves that silkworms eat, specifically the variety Morus alba cv. Mysore Local, grown only in the Mysore district. When a normal silkworm digests mulberry leaves, an enzyme in its midgut cleaves carotenoids into colourless compounds. The PM x CSR2 strain has a mutation that disables this enzyme, so the carotenoids pass through the gut wall unchanged and are transported to the silk glands. There, they bind to the fibroin protein through non-covalent interactions. The binding is stable enough to survive degumming, the hot-water process that removes sericin. Degummed PM x CSR2 silk retains its colour, whereas dyed silk often bleeds.

The sheen of Mysore silk — its characteristic gloss — is also partly due to the carotenoids. Lutein and β-carotene are crystalline in structure, and their alignment within the silk fibre scatters light differently than the amorphous arrangement of synthetic dyes. This creates a warm, almost metallic lustre that is impossible to achieve with chemical colourants.

Interestingly, the same mutation that gives PM x CSR2 its colour also slightly reduces tensile strength. Carotenoid molecules occupy space within the fibroin matrix, preventing the protein chains from packing as tightly. This makes the silk slightly less durable than white silk — a trade-off that connoisseurs accept for the sake of the colour.

Why No Other Region Can Copy It

Attempts to rear PM x CSR2 outside Mysore district have consistently failed. In the 1990s, the Central Silk Board tried to introduce the strain in Tamil Nadu's Krishnagiri district, which has a similar climate. The cocoons produced were smaller, the colour was paler, and the moths had lower fertility. The experiment was abandoned after three seasons.

The reason is a combination of climate and mulberry variety. Mysore district's elevation (roughly 770 metres above sea level) and its moderate temperatures — typically 20–30°C — are ideal for PM x CSR2. Above 32°C, the carotenoid-binding process becomes less efficient, and the silk emerges with a dull, yellowish-white colour. Below 18°C, the worms grow slowly and produce less silk.

The mulberry variety, Mysore Local, is also unique. It has higher carotenoid content than other Indian mulberry varieties, such as S-36 or V-1. When PM x CSR2 worms are fed on non-local mulberry, the colour intensity drops by an estimated 30–40%. The Karnataka State Sericulture Research and Development Institute maintains a germplasm bank of Mysore Local mulberry cuttings, but the variety is notoriously difficult to propagate in other soils.

Since 2005, Mysore silk has held a Geographical Indication (GI) tag, which legally restricts the use of the name to silk produced in the Mysore district from the PM x CSR2 strain. The GI certification requires that the entire process — from egg rearing to reeling — occur within the designated area. This has helped protect the strain's exclusivity, but enforcement is patchy. Some sellers market non-GI silk as "Mysore silk" based on dyeing alone, which dilutes the brand.

The Economics of a Living Heirloom

Rearing PM x CSR2 is not economically efficient. A single kilogram of raw silk requires roughly 3,000 to 3,500 cocoons. For PM x CSR2, the yield per 1,000 worms is only about 80–100 grams of raw silk, compared to 150–200 grams for high-yield hybrid strains like Bivoltine. The lower yield is partly due to the smaller cocoon size and partly to higher mortality — the strain is more susceptible to disease than hybrids.

Yet the premium price compensates. A certified GI-tagged Mysore silk saree typically costs three to four times more than an ordinary silk saree of similar weight. As of late 2024, a plain Mysore silk saree (without embroidery) retails for around ₹8,000–12,000, while a comparable non-Mysore silk saree sells for ₹2,500–4,000. The difference reflects not just the colour but also the labour-intensive rearing and the limited supply.

Weavers who specialise in Mysore silk rely on subsidies from the Karnataka government to sustain the strain. The state provides free disease-free layings (silkworm eggs) to registered rearers, as well as financial support for mulberry cultivation. Without these subsidies, many rearers would switch to higher-yielding hybrids. The Karnataka Silk Industries Corporation (KSIC), a state-owned enterprise, is the largest buyer of PM x CSR2 cocoons, guaranteeing a minimum price that is typically 20–30% above market rate for ordinary cocoons.

But the economics are fragile. In 2021, a pebrine outbreak — a microsporidian disease that affects silkworms — killed an estimated 30% of the PM x CSR2 stock at the Mysore Sericulture Station. The station had to rebuild its population from backup eggs stored in its gene bank. The incident highlighted the strain's vulnerability: because the genetic pool is small, a single disease event can wipe out years of breeding.

Threats to a Century-Old Lineage

Inbreeding depression is a growing concern. With a closed population of roughly 5,000–6,000 moths per generation, the effective population size is small. Inbreeding depression manifests as reduced hatch rates, smaller cocoons, and increased susceptibility to disease. Breeders attempt to manage this by periodically introducing individuals from the parent lines (Pure Mysore and CSR2) that have been cryopreserved as eggs, but the process is slow.

A 2023 survey by the Karnataka Sericulture Department found that only 12% of rearers are under 35. Many young rearers prefer the Bivoltine hybrid, which yields more silk per worm and is less labour-intensive. The average age of a Mysore silk rearer is estimated to be over 50, and few young people are entering the trade.

The Mysore Sericulture Station maintains a backup gene bank with cryopreserved eggs from the 1950s onward. In 2023, researchers at the station attempted to revitalise the strain by thawing and hatching eggs from the 1960s, crossing them with the current population to introduce genetic diversity. Early results were promising — the 2024 generation showed a 15% improvement in hatch rate — but the long-term viability is uncertain.

Climate change poses another threat. Average temperatures in Mysore have risen by about 0.5°C over the past three decades, and heatwaves are becoming more frequent. If temperatures regularly exceed 32°C during the rearing season (typically June–December), the strain's colour intensity could decline. Some researchers have suggested shifting the rearing season earlier or moving the station to a cooler location in the Western Ghats, but both options would require significant investment.

Preservation Versus Commercial Viability

The future of PM x CSR2 hinges on a fundamental tension: preserving its genetic purity versus making it commercially viable. On one hand, strict inbreeding preserves the unique colour but increases vulnerability to disease and reduces yield. On the other hand, introducing genetic diversity through outcrossing could improve hardiness but risks diluting the golden hue. For example, in 2018, researchers at the Central Sericultural Research and Training Institute in Mysore attempted to cross PM x CSR2 with a high-yield Bivoltine strain. The resulting hybrid produced 30% more silk per worm, but the colour was noticeably paler and less uniform, failing to meet the GI standard. The experiment was discontinued after two years.

Another trade-off involves rearing methods. Traditional rearing on bamboo trays with mulberry leaves is labour-intensive but produces the best colour. Modern rearing on artificial diets (soy-based powder mixed with mulberry leaf extract) reduces labour costs by 40% and disease incidence by 20%, but the silk from artificial diets has a slightly different carotenoid profile, resulting in a less vibrant yellow. A 2022 study published in the Journal of Sericulture Science found that artificial diet-reared PM x CSR2 silk had 25% lower lutein content than leaf-reared silk. Some weavers argue that this difference is noticeable to trained eyes, while others believe it is acceptable for mass-market products.

The Karnataka government faces a policy dilemma. Subsidies for PM x CSR2 rearing cost the state approximately ₹50 crore annually (about $6 million). Proponents argue that this is a small price to preserve a cultural heritage that generates ₹800 crore in saree sales. Critics counter that the same funds could support higher-yielding hybrids that would boost overall silk production and provide more income for farmers. A 2024 report by the Karnataka State Planning Board recommended reducing subsidies for PM x CSR2 by 10% per year over five years, while investing the savings in marketing and GI enforcement. The recommendation has been met with protests from weavers' associations, who fear that even a small reduction could push many rearers out of the industry.

Some innovative solutions are being explored. In 2023, a startup called SilkGen Labs in Bengaluru developed a method to increase carotenoid content in mulberry leaves by fertilising with a specific micronutrient mix. Field trials on a 10-acre plot near Mysore showed a 15% increase in cocoon colour intensity without any genetic modification. If scaled, this could allow rearers to maintain colour quality even if they switch to more resilient mulberry varieties. However, the micronutrient mix costs ₹2,000 per acre per season, which may be prohibitive for smallholders.

Another approach is to create a "brand premium" that directly rewards rearers for colour quality. In 2024, the Karnataka Silk Industries Corporation launched a pilot programme in three villages where rearers receive a 15% price bonus if their cocoons meet a spectrophotometric colour standard (L* a* b* values within a defined range). Early results show that 60% of participating rearers achieved the bonus, and the average colour uniformity improved. The programme is set to expand to 20 villages in 2025, but it requires expensive colour-measurement equipment (₹1.5 lakh per unit) and trained inspectors.

Ultimately, the survival of PM x CSR2 may depend on consumer willingness to pay a premium for authenticity. A 2023 survey of 500 saree buyers in Bengaluru found that 78% were willing to pay at least 50% more for a certified GI Mysore silk saree compared to a non-GI one, but only 22% could correctly identify the colour difference in a blind test. This suggests that the market value is driven more by brand and trust than by visual perception. If counterfeiters can produce convincing imitations through dyeing, the premium could erode.

The tension between preservation and commercial viability is not unique to Mysore silk. Similar challenges face other heritage products like Champagne (protected by appellation) and Parmigiano-Reggiano cheese. In those cases, strict regulations and strong consumer education have maintained premiums. For Mysore silk, the path forward likely involves a combination of stricter GI enforcement, investment in colour-measurement technology, and targeted subsidies for young rearers. Whether these measures will be enough to sustain a century-old silkworm strain remains an open question.

Where to See the Actual Moths

The Mysore Sericulture Station, located on the outskirts of Mysore city, is open to visitors by appointment. The station maintains a small museum with live displays of PM x CSR2 moths, eggs, and cocoons. Visitors can see the colour difference firsthand: the station's display cases show cocoons from PM x CSR2 alongside those from Bivoltine and other hybrids. The contrast is striking — the PM x CSR2 cocoons are a deep, warm gold, while the others are pale cream or white.

For a more hands-on experience, the silk-weaving centre at Srirangapatna, about 15 km from Mysore, offers demonstrations of traditional weaving using PM x CSR2 silk. The centre is run by the Karnataka State Handloom Development Corporation and sells certified GI-tagged sarees directly. During the annual Mysore Dasara exhibition (held in September–October), the Karnataka Silk Industries Corporation sets up a stall displaying raw silk from the station, along with information about the strain's history.

Buyers looking for authentic Mysore silk should look for the GI tag and the KSIC logo. The Karnataka Silk Industries Corporation operates retail outlets in Mysore, Bengaluru, and Delhi, and their products are traceable back to the rearing lot. Many online sellers claim to sell "Mysore silk" but use dyed white silk — a practice that the GI certification is meant to prevent, though enforcement remains imperfect.

The PM x CSR2 silkworm is not just a curiosity; it is a living document of agricultural history. For over a century, it has survived wars, economic shifts, and disease outbreaks. Whether it survives another century depends on the choices made by breeders, farmers, and consumers today. As with any heirloom, its value lies not in its age but in the care taken to preserve it.