The technique at the heart of the study is gynogenesis, the induction of embryo development from the female gametophyte without fertilization. When an unfertilized ovary is cultured on the right medium, the egg cell or an adjacent cell can be triggered to divide and form an embryo that carries only a single set of chromosomes. Such haploid plants are genetic blanks: every gene is present in just one copy. If breeders then double the chromosomes chemically, they obtain instantly homozygous, fully inbred lines in a single generation, a shortcut that in traditional breeding would demand six or more generations of selfing and selection. In speed-breeding programmes, gynogenesis is regarded as one of the fastest routes to haploid production, which is precisely why the IARI team focused on it.

Marigold, however, has been a reluctant participant. Earlier attempts in the same laboratory and elsewhere relied on androgenesis, culturing anthers or microspores to recover haploids from the male side, and on indirect gynogenesis, in which ovary explants first form callus that must then be coaxed to regenerate shoots. Indirect pathways carry a well-known penalty: callus phases introduce somaclonal variation, chromosome instability and genotype-dependent losses, so the plants that finally emerge are not always faithful copies of the mother line. The goal of the new work, published in the Indian Journal of Genetics and Plant Breeding, was to eliminate the callus stage altogether and regenerate haploid plantlets directly from cultured ovaries, something the authors describe as a first for this species.

The researchers worked with two hybrid genotypes of African marigold, DAMH-24 and DAMH-55, and systematically varied the two most influential levers in ovary culture: the hormonal composition of the medium and the stress pre-treatment applied to the buds before they entered culture. Unpollinated flower buds were excised and their ovaries placed on a modified Murashige and Skoog medium supplemented with the urea-derived cytokinin thidiazuron (TDZ) at five concentrations ranging from 0.25 to 1.50 mg per litre, combined with the auxin naphthaleneacetic acid (NAA) at either 0.20 or 0.50 mg per litre. TDZ is a potent morphoregulatory compound that mimics and often outperforms natural cytokinins, promoting cell division and organogenesis at remarkably low doses, which made it a logical candidate for triggering embryo-like divisions in the female gametophyte.

The second lever was cold shock. Before culturing, batches of buds were held at 4 degrees Celsius or 9 degrees Celsius for 0, 3, 7 or 10 days. Low-temperature pre-treatments are widely used in haploid induction because chilling appears to reprogramme gametophytic cells toward an embryogenic fate, partly by suspending normal developmental progression and partly by modulating stress-signalling pathways. In crops as diverse as sugar beet, onion, cucumber and cauliflower, cold pre-treatment has repeatedly improved the frequency of gynogenic or androgenic recovery, and the marigold study confirmed that the same principle applies on the female side of this ornamental species.

The winning combination was unambiguous. Ovaries of genotype DAMH-24 that were chilled at 4 degrees Celsius for seven days and then cultured on medium containing 0.75 mg per litre TDZ together with 0.20 mg per litre NAA produced the highest frequency of direct regeneration. In other words, the optimal recipe paired a moderate, sustained cold stress with a mid-range cytokinin dose and a low auxin level, a balance that appears to push the egg cell into division without diverting the explant into callus. Genotype mattered as well, a familiar theme in haploid work: responsiveness to gynogenesis is strongly heritable and varies dramatically between lines, which is why the two marigold hybrids were compared side by side from the outset.

Recovering plantlets is only half the battle; proving that they are genuinely haploid is the other half. The team deployed a three-tier verification strategy that is becoming standard in doubled-haploid research. First, stomatal guard cells were examined for chloroplast number, a rapid cytological proxy: albino or yellowish-green plantlets carried only 3 to 7 chloroplasts per guard cell, whereas vigorous green plantlets carried 10 to 14. Second, root-tip chromosome counts confirmed the division: putative haploids showed 2n = x = 12 chromosomes, exactly half the diploid complement of 2n = 2x = 24. Third, flow cytometry measured nuclear DNA content, with haploids displaying a 1 C value corresponding to a mean peak index of roughly 65 K, while diploids registered a 2 C value near 129 K. The concordance of all three markers left little doubt about the ploidy of each class of regenerant.

The yield, while modest, is a genuine proof of concept. Out of 77 plants regenerated directly from cultured ovaries, the researchers randomly selected 30 for ploidy analysis and confirmed that 4 of them, or 13.33 percent, were true haploids. The remainder were diploids, which in ovary culture can arise either from spontaneous chromosome doubling during early embryo development or from the accidental inclusion of maternal somatic tissue in the regenerative event. The authors are candid that the haploid frequency remains low and that the protocol will need further refinement before it becomes a routine breeding tool, but the decisive point is that haploid plants were recovered through a direct, callus-free pathway, avoiding the genetic noise that indirect regeneration introduces.

Importantly, the team did not attempt chromosome doubling in this study. The confirmed haploid plants are being maintained in vitro at ICAR-IARI, and diploidisation to create homozygous parental lines for F1 hybrid development is planned as the next stage of the programme. That step will typically involve treating haploid plantlets or their explants with a mitotic inhibitor such as colchicine, allowing the single chromosome set to replicate without cell division and thereby producing fully homozygous doubled haploids. Once achieved, those lines could serve as stable, uniform parents for hybrid marigold seed production, compressing years of pedigree inbreeding into a single laboratory cycle.

The broader significance of the work extends beyond one flower. Doubled-haploid technology has transformed breeding in wheat, barley, rapeseed and many vegetables, but ornamental crops have lagged behind, partly because their reproductive biology resists the standard anther- and microspore-culture toolkits. By demonstrating direct gynogenesis in African marigold, and by defining the cold-shock and hormonal parameters that make it work, the IARI group has added a valuable entry to a growing list of gynogenic systems in species such as onion, sugar beet, cucumber, cassava and chrysanthemum. For a crop whose petals colour everything from egg yolks to industrial lutein extracts, a faster route to pure parental lines is not merely a laboratory curiosity; it is a potential accelerant for an entire industry. The bottleneck in marigold hybrid breeding has not been eliminated, but for the first time it has been clearly broken open.

Subject of Research: Direct haploid plant regeneration via in vitro gynogenesis in African marigold (Tagetes erecta L.) for accelerated hybrid breeding

Article Title: Breaking the Bottleneck in African Marigold (Tagetes Erecta L.) Hybrid Breeding: Direct Haploid Regeneration via Gynogenesis

Article References: Arzoo, E., Bhatia, R., Dubey, K., Singh, K. P., Panwar, S., Talukdar, A., Singh, B., & Rao, M. (2026). Breaking the Bottleneck in African Marigold (Tagetes Erecta L.) Hybrid Breeding: Direct Haploid Regeneration via Gynogenesis. Indian Journal of Genetics and Plant Breeding. https://doi.org/10.1007/s44489-026-00055-8

Image Credits: AI Generated

DOI: 10.1007/s44489-026-00055-8

Keywords: African marigold, Tagetes erecta, gynogenesis, haploid, doubled haploid, thidiazuron, cold shock pre-treatment, ovary culture, ploidy analysis, F1 hybrid breeding, plant tissue culture, ICAR-IARI

The research, published as an open-access paper in the journal Discover Plants, set out to test whether exogenous applications of gibberellic acid, commonly abbreviated GA3, could counteract the damage that sodium chloride inflicts on African marigold, Tagetes erecta. The team, led by Kinza Nazir with Muhammad Umair and Zahoor Ahmad Sajid, ran a pot experiment between December 2024 and March 2025 in the wire house of the university’s Botanical Garden, using two-week-old marigold seedlings raised in a mixture of garden soil and coco peat. The design was deliberately comprehensive: sixteen treatment combinations, each replicated three times, spanning four levels of salt stress and four levels of hormone application.

The salt treatments were applied fifteen days after transplanting, when seedlings were irrigated with sodium chloride solutions at concentrations of zero, 50, 100 and 150 millimolar. At the same time, plants received foliar sprays of gibberellic acid at 0, 150, 250 or 350 parts per million, applied early in the morning every seven days for a full sixty days. The hormone was first dissolved in a small amount of absolute ethanol and then diluted with distilled water, with Tween 80 added as a surfactant to improve absorption through the leaves. Because marigold leaves lack a thick cuticle, the researchers note that GA3 can enter readily through the stomata, making foliar delivery an efficient route.

The results paint a clear picture of what salt does to a marigold. As sodium chloride concentrations rose, nearly every measured parameter declined. The number of side branches fell from 12.0 in unstressed control plants to 8.5 under the harshest 150 millimolar treatment. Bud production dropped from 6.8 per plant to just 3.2. Shoot length shrank from 25.5 centimeters to 18.5, root length fell from 15.5 centimeters to under 10, and both fresh and dry weights of shoots, roots and flowers declined in parallel. Flowering was delayed too: control plants opened their first blooms after 70 days, while plants under 150 millimolar salt took 80 days, and the heaviest salt treatments produced the fewest and lightest flowers.

When gibberellic acid entered the picture, the trajectory changed. Plants receiving the hormone alongside salt grew taller, bushier and heavier than their salt-stressed counterparts. Under 50 millimolar salt, shoot length rose to as much as 29.0 centimeters with the 250 ppm spray, exceeding even the unstressed control. Branch numbers recovered substantially, with the highest count of 15.0 side branches recorded in plants given 150 ppm GA3 without salt. Root growth responded as well, with the longest roots, 18.6 centimeters, appearing in plants treated with 350 ppm GA3 alone. Fresh shoot biomass climbed dramatically in some combinations, reaching 44 grams in plants sprayed with 250 ppm GA3 under no salt, compared with values around 17 to 19 grams under salt stress without hormone.

The flowering data were equally striking. Salt-stressed plants that received GA3 bloomed earlier than salt-stressed plants without it, with flowering times under salinity dropping from as late as 80 days to as few as 69 or 70 days depending on the combination. Flower counts per plant, which fell to 4.0 under moderate salt stress without hormone, rose to as high as 9.0 flowers per plant under 150 millimolar salt combined with 350 ppm GA3. The single most productive treatment overall was 350 ppm GA3 without salt, which yielded 13.0 flowers per plant, along with the highest fresh flower weight of 18.0 grams. Flower dry weight followed the same pattern, peaking at 3.4 grams in hormone-treated plants.

To understand the mechanism behind these visible improvements, the team measured the activity of three key antioxidant enzymes: peroxidase, superoxide dismutase and catalase. These enzymes form the plant’s first line of defense against reactive oxygen species, the chemically aggressive molecules, including superoxide radicals, hydroxyl radicals and hydrogen peroxide, that accumulate when salt stress disrupts cellular metabolism. At low concentrations these molecules act as signaling agents, but in excess they trigger peroxidation of lipids, proteins and nucleic acids, damaging the very machinery the cell needs to survive. Salt stress alone produced a mild rise in enzyme activity at 50 and 100 millimolar NaCl, but activity fell back at the harshest 150 millimolar level, suggesting the plant’s native defenses were being overwhelmed.

Gibberellic acid pushed those defenses back up. Superoxide dismutase activity, measured in units per milligram of protein, increased by as much as 72 percent in plants under 150 millimolar salt sprayed with 150 ppm GA3, with gains of 49 percent at 100 millimolar and 30 percent at 50 millimolar also recorded. Peroxidase activity rose by between 2 and 12 percent across the salt levels, while catalase activity climbed sharply, reaching 4.96 units per milliliter in plants under 100 millimolar salt with 150 ppm GA3, compared with 2.97 in salt-stressed plants without the hormone. The authors interpret this as evidence that GA3 strengthens the antioxidant system, protecting cells from oxidative damage and thereby allowing growth and flowering to continue under conditions that would otherwise suppress them.

The findings align with a growing body of literature on hormone-mediated stress relief. Previous work has shown that GA3 can improve ion homeostasis, maintain membrane permeability, enhance the accumulation of compatible osmolytes and regulate the expression of stress-responsive genes. Studies on okra, castor bean, potato and goldenrod have all reported similar benefits under salinity, and the marigold results extend that pattern to a commercially important ornamental. The authors also point to GA3-induced invertase activity in elongating shoots, which promotes the accumulation of hexoses needed for cell wall biosynthesis, as a plausible route by which the hormone accelerates growth even when salt is present in the root zone.

The practical implications are considerable. Marigold is not merely decorative: the genus supplies roughly 15 tons of essential oil annually for the flavor and fragrance industry, its flowers are a source of flavonoids and phenolic compounds for pharmaceutical use, and the plant has documented potential for phytoremediation of heavy metals such as zinc, cadmium and nickel. In Pakistan, where agriculture contributes 22.7 percent of GDP and salinity is a persistent threat to the Indus Basin, a cheap foliar spray that partially restores productivity on saline land could matter far beyond the flower bed. The study’s conclusion identifies 350 ppm as the most effective concentration for alleviating salt stress, though the authors caution that the protection is partial rather than complete, and they call for field trials across different species and soil types. Still, the message is clear: one of horticulture’s oldest tools, a simple hormone spray, may help ornamental crops hold their ground as the world’s soils grow steadily saltier.

Subject of Research: Mitigation of salt stress in marigold (Tagetes erecta) using exogenous gibberellic acid

Article Title: Gibberellic acid assisted modulations in growth, morphology and antioxidant activity of marigold (Tagetes erecta L.) grown in saline soil

Article References: Nazir, K., Umair, M., & Sajid, Z. A. (2026). Gibberellic acid assisted modulations in growth, morphology and antioxidant activity of marigold (Tagetes erecta L.) grown in saline soil. Discover Plants, 3(1), Article 406. https://doi.org/10.1007/s44372-026-00879-4

Image Credits: AI Generated

DOI: 10.1007/s44372-026-00879-4

Keywords: gibberellic acid, salinity stress, Tagetes erecta, marigold, antioxidant enzymes, plant growth regulators, NaCl, floriculture, reactive oxygen species, foliar spray, phytohormones, plant physiology

The research team, led by Snigdha Homroy and Rajni Chopra at the National Institute of Food Technology Entrepreneurship and Management in Kundli, Haryana, collected discarded Tagetes erecta flowers from a local temple within six to eight hours of generation and processed them within a day to minimise the loss of volatile phytochemicals. The flowers, which had a moisture content of approximately 88 percent, were gently crushed rather than milled to preserve the delicate glandular trichomes that house the oil-bearing volatiles. From this waste stream, the researchers extracted marigold essential oil using four different approaches: conventional hydro-distillation, ultrasound-assisted hydro-distillation, freeze-thaw-assisted hydro-distillation and solvent-free microwave extraction.

The choice of extraction route proved decisive. Hydro-distillation in a Clevenger-type apparatus for four hours yielded 0.0164 grams of oil per 100 grams of fresh flowers. When the flowers were first pre-treated with ultrasound at 500 watts and 20 kilohertz, acoustic cavitation, the violent formation and collapse of microscopic bubbles, tore open cell structures and improved solvent penetration, raising the yield by roughly 25 percent. A freeze-thaw pre-treatment, in which flowers were cycled between minus 80 degrees Celsius and room temperature three times, boosted the yield by about 17 percent, because ice crystals physically rupture cell walls and membranes during freezing, enlarging the porous network available to the extracting water.

Solvent-free microwave extraction, by contrast, performed poorly in this matrix, delivering a yield 85.3 percent lower than conventional hydro-distillation. The authors attribute this to the absence of added water and the limited intrinsic free moisture of the flowers, which restricted internal heating and volatilisation of the essential oil. The result is a useful reminder that green extraction technologies are not universally interchangeable: microwave methods that excel with aromatic herbs, as previous work on rosemary showed, can falter with high-moisture, fibrous floral waste. The relatively low absolute yields across all methods also reflect the use of whole flowers, which mix oil-rich tissues with fibrous, low-oil material, and the reporting of yields on a fresh-weight basis.

Chemical profiling by headspace gas chromatography-mass spectrometry identified 41 phytochemical constituents across the oils, with a profile rich in compounds prized for antioxidant, antimicrobial and anti-inflammatory activity. Nootkatone, limonene, tagetone, piperitone, ocimene, beta-caryophyllene and isoeugenol dominated, although their proportions shifted with the extraction method. Ultrasound-assisted hydro-distillation produced the highest overall content of key volatiles, enriching oxygenated sesquiterpenes and ketones such as nootkatone, which reached 11.15 percent, while freeze-thaw treatment similarly favoured sesquiterpenes. Microwave extraction skewed toward lighter hydrocarbons and phenolics, including isopentane and isoeugenol, which contribute aroma but are less relevant to oxidative protection.

The second half of the study tested whether this waste-derived oil could defend perilla seed oil, a cold-pressed, omega-3-rich oil whose high polyunsaturated fatty acid content makes it exceptionally vulnerable to rancidity. The researchers fortified the oil with marigold essential oil at 500, 1000 and 1500 parts per million and compared the results against 200 parts per million of tert-butylhydroquinone, or TBHQ, the synthetic antioxidant benchmark, and an untreated control. Samples were then subjected to a 20-day Schaal oven test at 60 degrees Celsius, an accelerated storage protocol that compresses months of ambient shelf-life degradation into weeks by speeding the same radical chain reactions that occur in normal storage.

Across every measure, the 1500 ppm marigold treatment performed impressively. Rancimat analysis showed a statistically significant, concentration-dependent extension of the induction period, indicating delayed oxidation onset. Viscosity, which climbs as oxidation generates polymeric degradation products, rose only to 37.1 centipoise in the marigold-fortified oil, compared with 40.3 centipoise in the untreated control. The untreated oil’s peroxide value, a gauge of primary oxidation, soared to 28.63 milliequivalents of oxygen per kilogram by day 20, whereas the marigold-supplemented oil held at 10.03 and TBHQ at 9.71. Acid value, p-anisidine value and conjugated triene content, which track hydrolysis and secondary aldehyde and ketone formation, followed the same pattern, with the highest marigold dose approaching TBHQ performance throughout.

Antioxidant capacity assays reinforced the picture. Untreated perilla oil lost radical-scavenging capacity rapidly, with DPPH inhibition falling from 84.42 to 74.35 percent and ABTS inhibition from 80.15 to 66.40 percent over the storage period. The 1500 ppm marigold sample, by contrast, retained 83.86 percent DPPH and 72.94 percent ABTS inhibition after 20 days, losses of less than seven percent, comparable to TBHQ-treated oil. The oil also preserved its golden carotenoid pigments better, retaining a yellow Lovibond value of 12.2 against 9.1 for the control. Hierarchical cluster analysis of all stability parameters grouped the control and 500 ppm samples together as low-stability outliers while placing the 1500 ppm marigold oil in the same high-stability cluster as TBHQ, a statistical confirmation that the floral waste extract can match a regulated synthetic preservative at its maximum permitted concentration.

The protective mechanism stems from the oil’s constellation of bioactive volatiles, which scavenge free radicals, chelate pro-oxidant metals and interrupt lipid peroxidation chain reactions, with synergy among compounds such as beta-caryophyllene, nootkatone and isoeugenol likely amplifying the effect. The study’s significance extends beyond food chemistry. It couples two sustainability goals at once: diverting a vast, culturally generated waste stream from landfill and offering food manufacturers a clean-label alternative to synthetic antioxidants such as BHA, BHT and TBHQ, whose potential carcinogenic, genotoxic and endocrine-disrupting effects have drawn increasing scrutiny in animal and mechanistic studies. The authors note that future work should clarify the underlying preservation mechanisms and extend testing to other oxidation-sensitive oils such as flaxseed and chia. If those trials succeed, the garlands left behind at temples across India could become a genuine industrial resource, turning ritual offerings into shelf life for the world’s healthiest cooking oils.

Subject of Research: Extraction of essential oil from marigold floral waste and its use as a natural antioxidant to stabilise polyunsaturated fatty acid-rich perilla seed oil.

Article Title: Valorisation of marigold floral waste for essential oil extraction and its application in stabilisation of PUFA rich perilla seed oil

Article References: Homroy, S., Madan, H., Sharma, S., Chopra, R., & Kumari, R. (2026). Valorisation of marigold floral waste for essential oil extraction and its application in stabilisation of PUFA rich perilla seed oil. Discover Green Chemistry, 1(1), Article 16. https://doi.org/10.1007/s44509-026-00015-1

Image Credits: AI Generated

DOI: 10.1007/s44509-026-00015-1

Keywords: marigold floral waste, Tagetes erecta, essential oil, hydro-distillation, ultrasound-assisted extraction, solvent-free microwave extraction, perilla seed oil, natural antioxidants, oxidative stability, TBHQ, omega-3, waste valorisation