Methods and Strategies for Exploration and Germplasm Collection

Every crop variety you see in a farmer’s field today traces its genetic roots back to wild ancestors, traditional landraces, and carefully preserved plant material. But what happens when those genetic roots start disappearing? That’s where germplasm exploration and collection steps in – a systematic effort to seek out, gather, and safeguard the genetic diversity that agriculture depends on. Without it, plant breeders would have no raw material to develop climate-resilient, disease-resistant, or high-yielding crop varieties. Let’s break down how this process works, why it matters, and what strategies scientists use to get it right.

What is germplasm and why does it matter? 🔗

Germplasm refers to the genetic material – seeds, tissues, plant parts, or DNA – that carries hereditary information from one generation to the next. It can come from cultivated crops, their wild relatives, traditional farmer-selected landraces, or even weedy species found at the edges of agricultural fields. According to the USDA’s National Genetic Resources Program, germplasm collections can range from wild species to elite domesticated breeding lines that have undergone extensive human selection.

The value of germplasm lies in the genetic variation it contains. A single wild relative of wheat growing on a hillside in Turkey might carry genes for drought tolerance that no modern variety possesses. A traditional rice landrace in northeast India might have natural resistance to a pest that devastates high-yielding commercial varieties. Without access to this diversity, crop improvement programmes hit a dead end. That’s why collecting and conserving germplasm is treated as a national responsibility by governments around the world.

The concept of plant exploration 🔗

Plant exploration is the organised search for plant genetic resources in their natural habitats or in farmers’ fields. It is not random – it requires careful planning, knowledge of taxonomy and ecology, and an understanding of where genetic diversity is most likely concentrated.

Vavilov’s pioneering contribution 🔗

The story of systematic germplasm exploration begins with Nikolai Vavilov, a Russian botanist and geneticist who, in the early 20th century, travelled across five continents collecting agrobiodiversity from remote regions. Based on his extensive collections and observations, Vavilov proposed that crop plants were not domesticated randomly across the globe. Instead, he identified specific geographic zones – known today as Vavilov Centres of Diversity – where particular crops showed the highest concentration of genetic variation.

Vavilov initially proposed three such centres in 1924 and eventually refined his theory to identify seven to eight major centres by 1940. These centres, located mostly in mountainous tropical and subtropical regions, include areas like the Fertile Crescent (wheat, barley), Mesoamerica (maize, beans), and the Indian subcontinent (rice, mango, citrus). His work laid the scientific foundation for all modern germplasm exploration missions by showing researchers exactly where to look for maximum diversity.

Types of germplasm collected 🔗

Not all germplasm is the same. The type of material collected during an exploration depends on the goals of the mission, the crops targeted, and what is already available in existing gene banks.

Landraces and traditional cultivars 🔗

Landraces are locally adapted varieties that farmers have selected and maintained over many generations. They are genetically diverse within a population and carry traits shaped by specific growing conditions, cultural preferences, and local pest pressures. As the USDA’s genebanking guide explains, landraces are rapidly disappearing because farmers are adopting uniform high-yielding varieties, shifting to different crops, or facing land-use changes driven by urbanisation. This makes their collection increasingly urgent.

Crop wild relatives 🔗

Crop wild relatives (CWR) are the wild ancestors or close botanical relatives of cultivated crops. They are treasure troves of useful genes – particularly for resistance to biotic and abiotic stresses – that are often absent in modern cultivated varieties. In India alone, researchers have documented over 320 wild relatives across cereals, legumes, oilseeds, fibre crops, spices, fruits, and vegetables. CWR are especially valuable because the closer a wild species is to a crop, the easier it is to transfer desirable traits through breeding.

Obsolete varieties and breeding lines 🔗

Older crop varieties that are no longer commercially grown can still harbour valuable genetic traits. These obsolete or heirloom varieties may possess resistance genes, quality traits, or adaptive features that were lost when newer varieties replaced them. Collectors also target advanced breeding lines and genetic stocks developed by research institutions, which may contain well-characterised genes useful for specific improvement objectives.

Planning a germplasm exploration mission 🔗

A successful collection mission doesn’t start in the field – it starts at the desk. Careful pre-exploration planning determines whether a mission captures meaningful diversity or returns with redundant material.

Identifying gaps in existing collections 🔗

The first step is a gap analysis – figuring out what’s missing from current gene bank holdings. This involves reviewing databases like GENESYS (a global portal for gene bank data), GRIN-Global (maintained by the USDA), and national gene bank records. Researchers look for taxonomic gaps (species or subspecies not yet collected), geographic gaps (regions never sampled), and ecological gaps (habitats or altitude ranges underrepresented). Modern GIS tools help map where diversity likely exists versus where collections have already been made.

Choosing the right location and timing 🔗

Location selection is driven by knowledge of the target crop’s centre of diversity, reports of interesting landraces in farming communities, herbarium records, and ecological data. Timing is equally critical – collectors must arrive when target species are at the correct maturity stage for seed or vegetative material harvest. For instance, collecting cereal seeds requires visiting during or just after grain maturity, while fruit tree germplasm may need to be collected as scion wood during dormancy.

Building the right team 🔗

Exploration teams typically include a crop specialist or plant breeder, a taxonomist for accurate species identification, and a local collaborator who knows the terrain and farming communities. Local partnerships are essential – farmers and indigenous communities often hold invaluable knowledge about where traditional varieties are grown and what traits they possess.

Sampling strategies for maximum genetic diversity 🔗

How samples are collected matters just as much as where they are collected. A poor sampling strategy can result in a gene bank accession that captures only a fraction of the available diversity.

Number and distribution of collection sites 🔗

The key question is: how many populations should be sampled, and how many individuals within each population? Marshall and Brown (1975) proposed an influential framework suggesting that the goal should be to capture locally common alleles – genetic variants present at moderate to high frequency in individual populations. According to the National Research Council’s guidance on collecting genetic resources, both the number of alleles and their frequency patterns within and between populations must be considered when designing sampling strategies.

Random versus targeted sampling 🔗

Within a given site, collectors can use random sampling (selecting plants at regular intervals or by chance) or targeted/biased sampling (deliberately selecting plants that look morphologically different or show unusual traits like disease resistance or early maturity). Random sampling gives a statistically unbiased snapshot of a population’s genetic makeup. Targeted sampling, on the other hand, is useful when the goal is to capture rare or extreme variants that random sampling might miss.

Sample size per population 🔗

For self-pollinating crops like wheat or rice, fewer individuals per site may suffice because genetic variation between plants within a population tends to be lower. For cross-pollinating crops like maize or many fruit trees, larger sample sizes are needed to capture the greater within-population diversity. A general recommendation is to collect seed from at least 30 to 50 individual plants per population for cross-pollinated species, and 15 to 20 for self-pollinated ones.

Methods of germplasm collection 🔗

The physical form of collected material varies depending on the species, its reproductive biology, and the storage capabilities of the receiving gene bank.

Seed collection 🔗

Seeds are the most common form of germplasm collection for annual and many perennial crops. They are relatively easy to transport, process, and store long-term under controlled temperature and humidity conditions. Orthodox seeds – those that tolerate drying and freezing – can be stored in gene banks for decades or even centuries. However, some species produce recalcitrant seeds that cannot survive desiccation or freezing, requiring alternative conservation approaches.

Vegetative material collection 🔗

Many important crops – such as banana, cassava, potato, sugarcane, and most fruit trees – are propagated vegetatively. For these species, collectors gather cuttings, tubers, bulbs, rhizomes, or other plant parts. Maintaining living collections of vegetatively propagated crops requires field gene banks, in-vitro culture facilities, or cryopreservation at ultra-low temperatures (−196°C in liquid nitrogen).

Whole plant and tissue samples 🔗

In some cases – particularly for woody perennials or species with complex reproductive biology – entire plants or tissue samples (meristems, embryos) are collected for in-vitro conservation. DNA samples and herbarium voucher specimens are also routinely collected alongside the primary germplasm to aid in identification and future molecular studies.

Documentation and passport data 🔗

Every sample collected during a germplasm exploration must be accompanied by detailed passport data – a standardised record of information about the sample and its collection site. This typically includes the collector’s name and number, collection date, geographic coordinates (latitude, longitude, altitude), habitat description, soil type, associated vegetation, local name of the variety, and any farmer knowledge about the plant’s traits or uses.

Good documentation is what transforms a bag of seeds into a useful genetic resource. Without it, breeders and researchers cannot determine where a sample came from, what conditions it was adapted to, or how it relates to other accessions. Modern explorations use GPS devices and mobile data-entry tools to ensure accuracy and efficiency in field data recording.

India’s germplasm exploration programme 🔗

India, one of the world’s 17 mega-biodiversity countries and home to a Vavilov centre of diversity, has a well-established system for germplasm exploration and collection led by the ICAR-National Bureau of Plant Genetic Resources (NBPGR) in New Delhi.

The Division of Plant Exploration and Germplasm Collection at NBPGR coordinates systematic explorations across India’s diverse agro-ecological zones. It focuses on priority crops, difficult terrains, tribal areas, and underexplored diversity-rich pockets. NBPGR uses GIS-based gap analysis to identify districts and taluks where specific crop diversity exists but has not yet been collected – a process completed for over 1,60,000 accessions across 24 major crops including rice, wheat, maize, millets, and legumes.

The National Genebank managed by NBPGR currently holds over 4,69,000 accessions belonging to more than 2,150 species, making it the second-largest gene bank in the world. This collection has been built through decades of domestic explorations and international germplasm exchange, and it serves as the foundation for India’s crop improvement programmes.

International frameworks governing germplasm collection 🔗

Germplasm collection is no longer a free-for-all activity. Since the Convention on Biological Diversity (CBD) came into force in 1993, countries exercise sovereign rights over their genetic resources. International germplasm exchange now operates under bilateral agreements that require prior informed consent and arrangements for equitable benefit sharing.

The International Treaty on Plant Genetic Resources for Food and Agriculture (ITPGRFA), adopted under the FAO, established a multilateral system for access and benefit sharing covering 64 of the world’s most important food and forage crops. This treaty facilitates germplasm exchange for research and breeding while ensuring that benefits are shared fairly. Any exploration mission – whether domestic or international – must comply with these legal frameworks, secure the necessary permits, and follow ethical guidelines for working with local communities.

Challenges in germplasm exploration today 🔗

Despite significant progress, germplasm exploration faces several ongoing challenges.

Genetic erosion 🔗

The rapid spread of genetically uniform modern varieties is replacing diverse landraces across farming landscapes worldwide. Urbanisation, deforestation, and climate change are further destroying the habitats of crop wild relatives. Every variety or wild population lost represents genes that can never be recovered.

Access restrictions 🔗

While legal frameworks like the CBD and ITPGRFA are necessary, they have also made germplasm exchange more complex and time-consuming. Obtaining collection permits, particularly for international missions, can take months or even years. This bureaucratic burden sometimes delays or prevents critical collection efforts.

Funding and capacity gaps 🔗

Germplasm exploration is labour-intensive and costly. Many developing countries – which are often the richest in crop diversity – lack the funding, trained personnel, and infrastructure needed for systematic exploration and long-term conservation. Sustained investment from national governments and international organisations remains essential.

Climate change pressures 🔗

Shifting temperature and rainfall patterns are altering the distribution of both cultivated and wild plant species. Some populations may disappear before they can be collected. This adds urgency to exploration efforts and calls for predictive modelling to identify populations most at risk.

The road ahead: technology and collaboration 🔗

Modern tools are transforming germplasm exploration. GIS and remote sensing help pinpoint diversity-rich areas and guide collection missions more efficiently. Molecular markers and genomic tools allow researchers to assess the genetic uniqueness of collected samples quickly, reducing redundancy in gene bank holdings. Mobile applications simplify field data collection, and global databases like GENESYS enable better coordination among gene banks worldwide.

Perhaps most importantly, there is growing recognition that farmers and indigenous communities are not just sources of germplasm but active custodians of genetic diversity. Participatory approaches that involve local communities in conservation – sometimes called on-farm conservation – complement gene bank efforts and keep traditional varieties alive in their natural agricultural context.

What do you think? With modern agriculture increasingly relying on a narrow genetic base, how can we better balance the push for high-yielding uniformity with the need to preserve the genetic diversity that keeps our food supply resilient? And in your region, are there traditional crop varieties or wild plant species that deserve more attention from collectors and conservationists?

References

1. https://en.wikipedia.org/wiki/Germplasm
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC10385243/
3. https://en.wikipedia.org/wiki/Vavilov_center
4. https://colostate.pressbooks.pub/fundamentalsofplantgenebanking/chapter/planning-a-plant-exploration/
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC7907825/
6. https://www.genesys-pgr.org
7. https://nap.nationalacademies.org/read/2116/chapter/8
8. https://www.mdpi.com/2071-1050/13/12/6743
9. https://nbpgr.org.in/nbpgr2023/plant-exploration-collection-new-delhi/
10. https://nbpgr.org.in/nbpgr2023/germplasm-conservation-division-new-delhi/
11. https://www.fao.org/4/i1500e/India.pdf