Neem’s Variety Boom Outpaces the Legal Tests Meant to Protect It

Neem, the hardy multipurpose tree of the Indian subcontinent, has become the focus of a rapidly expanding varietal improvement effort. Its seed kernel carries 40 to 50 percent oil and up to 1.5 percent azadirachtin, a limonoid bioinsecticide whose value spans pest control, pharmaceuticals and fertilizer chemistry. When the Government of India decided in 2015 to promote 100 percent neem-coated urea, demand for quality neem oil surged, because the coating slows urea hydrolysis, prolongs nitrogen availability and improves nitrogen-use efficiency. That policy shift triggered a wave of genetic improvement, culminating in the 2021 release of six elite neem varieties by the Forest Research Institute in Dehradun in collaboration with the Indian Farmers Fertiliser Cooperative Limited. The varieties flower and fruit within two to three years, with oil content ranging from 35.44 to 43.51 percent and azadirachtin concentrations from 6047 to 9760 parts per million.

Yet the legal machinery meant to safeguard these gains is struggling to keep pace. Under India’s sui generis Protection of Plant Varieties and Farmers’ Rights Act of 2001, distinctness, uniformity and stability, known collectively as DUS, form the mandatory criteria for registering and protecting a new variety. The framework mirrors the principles of the Union for the Protection of New Varieties of Plants, established in 1961, which requires that a candidate variety be reliably distinguishable from existing ones, exhibit adequate uniformity and maintain its defining characteristics over successive generations. For annual crops, standardized DUS protocols make this a routine exercise. For neem, a perennial tree with an outcrossing breeding system and pronounced phenotypic plasticity, it is anything but routine.

A new systematic review published in Discover Plants confronts this mismatch directly. Led by researchers at the Forest Research Institute, the review followed PRISMA 2020 guidelines, searching Crossref, PubMed, Scopus, Google Scholar and Semantic Scholar for literature published between January 2000 and March 2026. From 1267 identified records, 1030 remained after duplicate removal, 820 full-text articles were assessed, and 142 studies met the predefined selection criteria. Because the underlying data were too heterogeneous for statistical pooling, the authors synthesized the evidence through structured qualitative thematic analysis, complemented by bibliometric network analysis to map research trends and knowledge gaps in Azadirachta indica research.

The review’s central finding is that the current neem DUS descriptor set, while a genuine foundation, has never been systematically validated. The notified guidelines include ten quantitative, four qualitative and seven pseudo-qualitative characteristics covering tree habit, leaf morphology, flowering behaviour, fruit traits and seed characteristics. But the usefulness of a descriptor for DUS testing depends not simply on whether it varies among genotypes. It must be consistent and repeatable, allow clear distinction among varieties and remain stable over successive evaluation cycles. For neem, the relative discriminatory power of individual descriptors has never been ranked, leaving examiners without evidence on which traits truly represent varietal identity rather than environmental noise.

Time itself distorts the picture. Trees delay the expression of stable morphological traits through extended juvenile phases, making DUS testing resource-intensive relative to annual crops. Neem is more favourable than most timber species, but still demanding: unimproved seed sources typically require four to five years to fruit, whereas the FRI-IFFCO selections flower and fruit within two to three years. Even so, descriptors dependent on mature fruit and seed cannot be scored before the third year, and two independent growing cycles of comparable fruiting intensity stretch a complete test to five years or more. The irony is sharp: precocity is itself the single most valuable distinguishing feature of the released material, yet no descriptor in the notified list records age at first flowering, duration of flowering or duration of fruiting. Any defensible protocol must also specify the minimum tree age at which each descriptor becomes scorable, because the same character scored on a three-year-old and a ten-year-old tree yields different states.

Environment compounds the problem. Azadirachtin content varies several-fold among Indian provenances, seed and oil traits differ significantly among collections from Tamil Nadu and Karnataka, and multi-zone evaluations show that seed and biochemical traits respond strongly to differing agro-climatic conditions. Even neem’s evergreen habit is conditional, with leaves shed during extreme dry spells, which means leaf-based descriptors, eight of the twenty-four notified characters, are scorable only within a defined seasonal window and only in years without severe drought. Recognizing that single-site data cannot separate genotype from environment, the FRI-IFFCO progeny trials were established at three contrasting sites, Kalol in Gujarat, Tikamgarh in Madhya Pradesh and Rajsamand in Rajasthan, from 2016 to 2017 in a randomized block design. DUS characters have been assessed over three independent growing cycles on 65 genotypes at all locations, though analysis and interpretation in terms of DUS characterization remain in progress.

Uniformity poses a subtler conceptual challenge rooted in neem’s breeding system. The tree is insect-pollinated and largely outcrossing, and morphological variation across 32 neem populations has been interpreted as potentially useful for estimating outcrossing rates and paternity in seed orchards, in other words, as evidence of segregation rather than varietal identity. This bears directly on registration practice: uniformity assessed on open-pollinated seedling progenies measures the breeding system as much as the variety, whereas uniformity assessed on clonally propagated material is guaranteed by the propagation method itself and is therefore uninformative. A defensible neem protocol must state which propagation type each candidate is submitted as, and define off-type tolerance limits and sample sizes separately for seedling and clonal submissions. No such distinction appears in the notified guidelines.

Operational infrastructure is missing as well. The notified guidelines assign expression states without designating example varieties, so an examiner has no physical or photographic standard against which to score a semi-upright habit or a medium oil content. No centre has been designated to maintain a national neem reference collection across the three or more growing cycles a woody perennial test requires. Until example varieties are designated and a reference collection is curated, the descriptor list cannot be applied reproducibly by different examiners at different centres, an operational reason why so few tree varieties have completed registration despite an adequate statutory framework.

Biochemistry offers a promising way forward, and the review documents its genetic basis. Azadirachtin has the strongest evidence for genetic control: significant variation exists among provenances and individual trees growing under similar environmental conditions, and progeny-based studies report high heritability and substantial genetic advance for total azadirachtin and its fractions, indicating real potential for selection. Nimbin and salannin also vary widely among provenances and among trees within the same provenance, suggesting a genetic component, though direct heritability estimates remain limited and should be confirmed through progeny or clonal trials. These metabolites could act as valuable complementary descriptors when morphological traits fail to discriminate closely related elite varieties, but the review is explicit that they would enter the formal DUS framework only after demonstrating adequate repeatability, discriminatory power and analytical reproducibility.

The review closes with a research agenda that treats the descriptor list as a hierarchical system rather than an undifferentiated catalogue. Priorities include validating existing morphological descriptors across multiple environments and developmental stages, explicitly quantifying genotype-by-environment interactions using variance components and stability statistics, standardizing measurement protocols for quantitative and pseudo-qualitative characters, and evaluating economically important biochemical traits for stability and discriminatory value. DNA-based approaches, supported by a reported genome assembly for neem, could complement phenotypic testing through SNPs, SSRs and genome-wide markers for establishing genetic identity and reference databases, though molecular markers should remain complementary to conventional descriptors rather than an immediate replacement. Digital phenotyping and image analysis, already under consideration by UPOV for DUS examination, could quantify leaf area, leaflet shape, fruit dimensions and canopy architecture while building permanent digital records of reference varieties. The authors argue that an evidence-based integration of stable morphological descriptors with validated biochemical, molecular and digital information could yield a future-ready DUS framework for neem, with applications reaching far beyond registration into breeding, germplasm conservation, varietal traceability and the sustainable deployment of improved planting material.

Subject of Research: DUS characterization and variety protection in neem

Article Title: Advancing DUS characterization of neem through systematic gap analysis and setting future research priorities

Article References: Mahajan, A., Rana, A., Jyoti, J., Kumar, Y., Kant, R., & Kumar, A. (2026). Advancing DUS characterization of neem through systematic gap analysis and setting future research priorities. Discover Plants, 3(1), Article 494. https://doi.org/10.1007/s44372-026-00926-0

Image Credits: AI Generated

DOI: 10.1007/s44372-026-00926-0

Keywords: neem, DUS testing, plant variety protection, azadirachtin, genotype-by-environment interaction, molecular markers, digital phenotyping, germplasm conservation, Forest Research Institute, PPV&FR Act, biochemical descriptors, tree breeding