Mulberry occupies a uniquely pivotal position in sericulture, the agricultural practice of raising silkworms for silk production. Unlike livestock that can be fed a varied diet, the silkworm Bombyx mori is a monophagous feeder, meaning it eats mulberry leaves and essentially nothing else. That biological constraint makes leaf quality the single most important input variable a sericulture farmer controls. The nutritional composition of mulberry foliage directly governs silkworm growth rates, larval health, cocoon yield, and ultimately the fineness and strength of the silk filament that gets reeled from each cocoon. A better leaf, in other words, translates almost linearly into better silk and better livelihoods for the millions of people, particularly in India and China, who depend on the silk trade.

The problem facing breeders is that mulberry is notoriously difficult to improve through conventional means. Most cultivated mulberry is propagated vegetatively from cuttings rather than grown from seed, which preserves desirable traits but also freezes the genetic diversity of the crop. Many of the traits that matter most to sericulture, such as leaf protein content, sugar levels, and moisture retention, are polygenic, controlled by many genes acting together rather than by a single mutation. Traditional crossbreeding can shuffle these genes, but the process is slow and constrained by the limited variation available in existing germplasm. This is where mutation breeding enters the picture. By exposing plant material to physical mutagens such as gamma rays, breeders can induce novel genetic permutations and combinations that would rarely, if ever, arise spontaneously, effectively manufacturing the raw genetic variation that selection programs need.

In the new study, researchers H. L. Ramesh, Munirajappa, and V. N. Yoganandamurthy subjected juvenile twigs of the S54 mulberry variety to a gradient of gamma irradiation doses spanning 1 to 10 kR, delivered in a cobalt-60 gamma chamber at the Indian Institute of Horticulture Research in Bengaluru. The irradiated cuttings were then cultivated in a randomized block design, a standard experimental layout that controls for environmental variation across the field, to raise the first mutant generation. From those plants, the team established putative mutant lines, so named because they carry induced changes whose genetic basis has not yet been fully characterized, and advanced them to the M2 generation, the second filial generation after mutagenesis in which recessive mutations typically begin to reveal themselves phenotypically.

The biochemical analysis of the resulting leaves revealed a striking dose-dependent pattern. While lower and higher doses produced variable effects, the 7 kR treatment stood out as a consistent winner. Leaves from cuttings treated at this dose showed significant improvements across a battery of biochemical parameters, including total protein content, soluble sugars, phenolic compounds, total chlorophyll, and moisture content. Critically, these improvements held across all three leaf maturity classes examined, from tender young leaves to coarse mature foliage. That consistency matters because silkworms are typically fed leaves of varying maturity during different larval stages, and a mutation that improves only one leaf class would offer limited practical benefit. The methods used to quantify these constituents draw on classic plant biochemistry protocols, including protein estimation with Folin’s phenol reagent, carbohydrate measurement with anthrone reagent, and chlorophyll extraction without maceration, techniques that have anchored plant physiology research for decades.

Phenolic compounds deserve particular attention in this context. These plant secondary metabolites serve multiple roles, acting as antioxidants within the plant and as bioactive compounds that can influence the physiology of organisms that consume the foliage. Previous research on mulberry has documented that the leaves are rich in polyphenolic compounds whose concentrations vary by variety, harvest period, and processing. The finding that gamma irradiation elevated phenolic content in the S54 mutants aligns with earlier reports from the same research group, who had previously shown in M5 generation mulberry mutants that irradiation enhanced leaf bioactive components. Elevated chlorophyll content, meanwhile, hints at improved photosynthetic capacity, which could underpin the observed increases in sugars and proteins by providing more carbon and energy for biosynthesis.

To test whether these biochemical gains actually mattered to the end consumer of the leaf, the silkworm itself, the researchers conducted a bioassay using crossbred PM x NB4D2 silkworms, a commercially relevant hybrid combination. Larvae were reared on leaves from the different irradiated treatments, and their commercial traits were measured at maturity. The results were unambiguous: silkworms fed the 7 kR mutant leaves displayed marked enhancements in cocoon weight, shell weight, pupal weight, filament length, denier, and renditta. Each of these metrics tells part of the silk quality story. Cocoon and shell weights reflect how much raw material the insect invested in its silk. Filament length determines how much continuous silk thread can be reeled from a single cocoon. Denier measures filament thickness, and renditta expresses how many kilograms of cocoons are required to produce one kilogram of raw silk, with lower values indicating greater efficiency.

The logic connecting leaf chemistry to silk output runs through silkworm nutritional physiology. Decades of research have established that silkworm growth and silk synthesis depend on the balance of proteins, amino acids, carbohydrates, and moisture in the diet. Proteins and free amino acids feed directly into silk fibroin and sericin production in the silk glands, while soluble sugars fuel the energetically expensive process of spinning. Leaf moisture influences how efficiently larvae can digest and assimilate their food. When the 7 kR mutant leaves delivered elevated levels of these constituents simultaneously, the silkworms converted the improved diet into heavier cocoons and longer, finer filaments, exactly the outcome a sericulture improvement program hopes to achieve.

The study builds on a substantial body of mutation breeding work in mulberry and other crops. Earlier investigations demonstrated that acute gamma irradiation produces variety-specific mutation rates and spectra in mulberry, and that mutagens can induce useful mutations in the S54 variety as early as the M1 generation. Comparable gamma-induced improvements have been documented in crops ranging from cowpea to banana, and radiation has even been used to degrade chitosan for application to mulberry plants as an elicitor. What distinguishes the new work is the full-chain demonstration, from irradiation through phytochemical profiling to a silkworm bioassay measuring commercial silk traits, providing end-to-end evidence that the induced mutation is agronomically meaningful rather than merely a laboratory curiosity.

For the silk industry, the implications are tantalizing. India is one of the world’s largest silk producers, and improvements in cocoon yield and silk quality ripple through an entire value chain that supports rural economies. A mulberry line that produces more nutritious leaves could raise productivity without expanding acreage, irrigation, or fertilizer inputs, an appealing proposition in an era of climate stress and land pressure. The researchers note that mulberry improvement through mutagenesis and polyploidy induction remains an active frontier, particularly as breeders seek varieties suited to changing agro-climatic conditions. The 7 kR S54 putative mutant now joins a growing roster of radiation-derived plant lines whose value lies not in dramatic visible transformations, but in the quiet arithmetic of biochemistry: a few more grams of protein per leaf, a few more meters of filament per cocoon, and a stronger, brighter thread of silk at the end of it all.

Subject of Research: Gamma irradiation-induced mutation breeding of S54 mulberry and its effects on leaf phytochemistry and silkworm silk production traits

Article Title: Genotypic variation, Phytochemical Composition and Bioassay Analysis in Gamma Irradiated S54 Mulberry (morus) Putative Mutant

Article References: Ramesh, H. L., Munirajappa, & Yoganandamurthy, V. N. (2026). Genotypic variation, Phytochemical Composition and Bioassay Analysis in Gamma Irradiated S54 Mulberry (morus) Putative Mutant. Indian Journal of Genetics and Plant Breeding, 86(1), 93-102. https://doi.org/10.1007/s44489-026-00002-7

Image Credits: AI Generated

DOI: 10.1007/s44489-026-00002-7

Keywords: mulberry, gamma irradiation, mutation breeding, sericulture, silkworm, phytochemicals, S54 mutant, cocoon yield, silk quality, plant biochemistry, M2 generation, genetic variation