But how is it accomplished when billions of plants are involved, and exchanges take place at the national, or even international scale? A new publication asks this question for Southeast Asian cassava, the backbone of production for millions of smallholder farmers. The 3.5 million hectares of cassava planted every year in Southeast Asia requires ~ 40 billion plants to be planted in the right place, and at the right time. But how seed get there without the existence of a formal seed sector remains surprisingly poorly understood. A new study by CIAT and RTB colleagues determined to find out more. <center> <h3>Cassava production over time (1961-2014). Mouse over the data for more detail, or click on the legend to switch regions on or off and take a closer look.</h3></center> We often glimpse the silhouettes of seed movement by observing side effects - a new variety appears far from where it originated, or a slow-moving pest or disease hopscotches between distant areas. These hints indicate that cassava stems are being moved, but how and by whom remained a mystery until recently. Led by the International Center for Tropical Agriculture (CIAT), a team of researchers undertook the first comprehensive evaluation of cassava seed use and exchange in adjacent Vietnam and Cambodia. But why is studying cassava seed a priority? To explain we need a quick refresher on plant biology. In agriculture the word ‘seed’ is often a catchall for ‘propagules’ – all the different types of plant tissues which can be used to produce new crops. These include seeds, stems, sections of fruits, roots, rhizomes, and others. For many root and tuber crops, we have mostly done away with the use of true seeds altogether through the special ability of ‘vegetative propagation’. Thousands of years ago, our ancestors discovered that some plants could be snipped, planted, and re-sprout perfect little clones. The advantages of vegetative propagation proved to be so great that this method still produces many of the food plants we enjoy today. Potatoes, bananas, yams, wine grapes, many commercial fruit and timber trees, saffron, cassava – all are routinely referred to as vegetatively propagated crops. Between cropping seasons, cassava planting material is stored in 2-3m long stems. This is the cassava ‘seed’ (I use both ‘seed’ and ‘stems’ interchangeably in this article). Once the farmer decides it is time to plant, stems are cut into ~15 cm sections and placed in the earth. Sensing contact with water and soil, each stem piece grows new roots and leaves. In 9-12 months, the plant is mature and ready for harvest, and the cycle continues. But the repetitive cycle of cutting and replanting also poses risks. Mother plants may acquire diseases during their lifetime, and then pass them on to daughter plants in the following generation. Insect pests can easily hitchhike on the big, bulky planting stems. The gradual decline in seed quality caused by these accumulating factors - in particular viruses - is referred to as ‘seed degeneration,’ and makes studying seed systems very important. In Vietnam and Cambodia we conducted 840 farmer interviews to gather information on seed use in 31 districts in the two target countries. We asked farmers about their seed use during the past year, including all exchanges they made with others (both who they acquired seed from, and who they gave it to). The interactive graph below allows you to explore some data from 4 contrasting provinces with different production characteristics (100 surveys per province): <center><!-- --> <table style="width:65%"><!-- --> <tr><!-- --> <th>Country</th><!-- --> <th>Province</th><!-- --> <th>Production intensity</th><!-- --> </tr><!-- --> <tr><!-- --> <td>Cambodia</td><!-- --> <td>Battambang</td><!-- --> <td>High</td><!-- --> </tr><!-- --> <tr><!-- --> <td>Cambodia</td><!-- --> <td>Ratanakiri</td><!-- --> <td>Low</td><!-- --> </tr><!-- --><tr><!-- --> <td>Vietnam</td><!-- --> <td>Tay Ninh</td><!-- --> <td>High</td><!-- --> </tr><!-- --> <tr><!-- --> <td>Vietnam</td><!-- --> <td>Dak Lak</td><!-- --> <td>Low</td><!-- --> </tr><!-- --></table> <!-- --> </center><!-- --><center><!-- --><head><!-- --><meta charset="utf-8" /><!-- --><!-- --><!-- --><link href="data:text/css;charset=utf-8,%2Eparset%20%2Edimension%20%7B%20cursor%3A%20ns%2Dresize%3B%20%7D%0A%2Eparset%20%2Ecategory%20%7B%20cursor%3A%20ew%2Dresize%3B%20%7D%0A%2Eparset%20%2Edimension%20tspan%2Ename%20%7B%20font%2Dsize%3A%201%2E5em%3B%20fill%3A%20%23333%3B%20font%2Dweight%3A%20bold%3B%20%7D%0A%2Eparset%20%2Edimension%20tspan%2Esort%20%7B%20fill%3A%20%23000%3B%20cursor%3A%20pointer%3B%20opacity%3A%200%3B%20%7D%0A%2Eparset%20%2Edimension%20tspan%2Esort%3Ahover%20%7B%20fill%3A%20%23333%3B%20%7D%0A%2Eparset%20%2Edimension%3Ahover%20tspan%2Ename%20%7B%20fill%3A%20%23000%3B%20%7D%0A%2Eparset%20%2Edimension%3Ahover%20tspan%2Esort%20%7B%20opacity%3A%201%3B%20%7D%0A%2Eparset%20%2Edimension%20line%20%7B%20stroke%3A%20%23000%3B%20%7D%0A%2Eparset%20%2Edimension%20rect%20%7B%20stroke%3A%20none%3B%20fill%2Dopacity%3A%200%3B%20%7D%0A%2Eparset%20%2Edimension%20%3E%20rect%2C%20%2Ecategory%2Dbackground%20%7B%20fill%3A%20%23fff%3B%20%7D%0A%2Eparset%20%2Edimension%20%3E%20rect%20%7B%20display%3A%20none%3B%20%7D%0A%2Eparset%20%2Ecategory%3Ahover%20rect%20%7B%20fill%2Dopacity%3A%20%2E3%3B%20%7D%0A%2Eparset%20%2Edimension%3Ahover%20%3E%20rect%20%7B%20fill%2Dopacity%3A%20%2E3%3B%20%7D%0A%2Eparset%20%2Eribbon%20path%20%7B%20stroke%2Dopacity%3A%200%3B%20fill%2Dopacity%3A%20%2E5%3B%20%7D%0A%2Eparset%20%2Eribbon%20path%2Eactive%20%7B%20fill%2Dopacity%3A%20%2E9%3B%20%7D%0A%2Eparset%20%2Eribbon%2Dmouse%20path%20%7B%20fill%2Dopacity%3A%200%3B%20%7D%0A%2Eparset%20%2Ecategory%2D0%20%7B%20fill%3A%20%231f77b4%3B%20stroke%3A%20%231f77b4%3B%20%7D%0A%2Eparset%20%2Ecategory%2D1%20%7B%20fill%3A%20%23ff7f0e%3B%20stroke%3A%20%23ff7f0e%3B%20%7D%0A%2Eparset%20%2Ecategory%2D2%20%7B%20fill%3A%20%232ca02c%3B%20stroke%3A%20%232ca02c%3B%20%7D%0A%2Eparset%20%2Ecategory%2D3%20%7B%20fill%3A%20%23d62728%3B%20stroke%3A%20%23d62728%3B%20%7D%0A%2Eparset%20%2Ecategory%2D4%20%7B%20fill%3A%20%239467bd%3B%20stroke%3A%20%239467bd%3B%20%7D%0A%2Eparset%20%2Ecategory%2D5%20%7B%20fill%3A%20%238c564b%3B%20stroke%3A%20%238c564b%3B%20%7D%0A%2Eparset%20%2Ecategory%2D6%20%7B%20fill%3A%20%23e377c2%3B%20stroke%3A%20%23e377c2%3B%20%7D%0A%2Eparset%20%2Ecategory%2D7%20%7B%20fill%3A%20%237f7f7f%3B%20stroke%3A%20%237f7f7f%3B%20%7D%0A%2Eparset%20%2Ecategory%2D8%20%7B%20fill%3A%20%23bcbd22%3B%20stroke%3A%20%23bcbd22%3B%20%7D%0A%2Eparset%20%2Ecategory%2D9%20%7B%20fill%3A%20%2317becf%3B%20stroke%3A%20%2317becf%3B%20%7D%0A%2Eparsets%2Etooltip%20%7B%0Abackground%2Dcolor%3A%20rgba%28242%2C%20242%2C%20242%2C%20%2E6%29%3B%0Aposition%3A%20absolute%3B%0Apadding%3A%205px%3B%0Aopacity%3A%201%3B%0A%7D%0A" rel="stylesheet" /><!-- --><!-- --><!-- --><!-- --></head><!-- --><body style="background-color:white;"><!-- -->
<!-- --></div><!-- -->{"x":{"data":{"A) Surveyed province":,"C) Seed acquired from":,"B) Surveyed farmer gender":},"options":{"spacing":0,"tension":0.4}},"evals":,"jsHooks":}<!-- -->{"viewer":{"width":600,"height":300,"padding":15,"fill":false},"browser":{"width":600,"height":300,"padding":40,"fill":false}}<!-- --></body><!-- --><center><h3>Farmer seed acquisitions in 2016-17. You can interact with the data by clicking and dragging the categories. Try rearranging A, B, C to make the colors emphasize different categories.</h3></center><!-- --></center><!-- --> Some differences between provinces are clear. Seed exchanges in the high production intensity sites in both countries (Tay Ninh and Dak Lak) are overwhelmingly managed by male farmers, while the low intensity production sites have quite equal male and female participation. Try rearranging the categories from top down in the order B, C, A. The result shows that male farmers manage most of the seed acquisition from traders, and only men interacted with the other 'commercial' seed sources such as collection points (where roots are bought in the village), starch factories, or government research organizations. This shows that, in addition to the biological importance of seed systems, social factors such as gender, trust, and accessibility influence seed exchange. The below graph is the same type, but this time showing who farmers provided seed to. <center><!-- --><head><!-- --><meta charset="utf-8" /><!-- --><!-- --><!-- --><link href="data:text/css;charset=utf-8,%2Eparset%20%2Edimension%20%7B%20cursor%3A%20ns%2Dresize%3B%20%7D%0A%2Eparset%20%2Ecategory%20%7B%20cursor%3A%20ew%2Dresize%3B%20%7D%0A%2Eparset%20%2Edimension%20tspan%2Ename%20%7B%20font%2Dsize%3A%201%2E5em%3B%20fill%3A%20%23333%3B%20font%2Dweight%3A%20bold%3B%20%7D%0A%2Eparset%20%2Edimension%20tspan%2Esort%20%7B%20fill%3A%20%23000%3B%20cursor%3A%20pointer%3B%20opacity%3A%200%3B%20%7D%0A%2Eparset%20%2Edimension%20tspan%2Esort%3Ahover%20%7B%20fill%3A%20%23333%3B%20%7D%0A%2Eparset%20%2Edimension%3Ahover%20tspan%2Ename%20%7B%20fill%3A%20%23000%3B%20%7D%0A%2Eparset%20%2Edimension%3Ahover%20tspan%2Esort%20%7B%20opacity%3A%201%3B%20%7D%0A%2Eparset%20%2Edimension%20line%20%7B%20stroke%3A%20%23000%3B%20%7D%0A%2Eparset%20%2Edimension%20rect%20%7B%20stroke%3A%20none%3B%20fill%2Dopacity%3A%200%3B%20%7D%0A%2Eparset%20%2Edimension%20%3E%20rect%2C%20%2Ecategory%2Dbackground%20%7B%20fill%3A%20%23fff%3B%20%7D%0A%2Eparset%20%2Edimension%20%3E%20rect%20%7B%20display%3A%20none%3B%20%7D%0A%2Eparset%20%2Ecategory%3Ahover%20rect%20%7B%20fill%2Dopacity%3A%20%2E3%3B%20%7D%0A%2Eparset%20%2Edimension%3Ahover%20%3E%20rect%20%7B%20fill%2Dopacity%3A%20%2E3%3B%20%7D%0A%2Eparset%20%2Eribbon%20path%20%7B%20stroke%2Dopacity%3A%200%3B%20fill%2Dopacity%3A%20%2E5%3B%20%7D%0A%2Eparset%20%2Eribbon%20path%2Eactive%20%7B%20fill%2Dopacity%3A%20%2E9%3B%20%7D%0A%2Eparset%20%2Eribbon%2Dmouse%20path%20%7B%20fill%2Dopacity%3A%200%3B%20%7D%0A%2Eparset%20%2Ecategory%2D0%20%7B%20fill%3A%20%231f77b4%3B%20stroke%3A%20%231f77b4%3B%20%7D%0A%2Eparset%20%2Ecategory%2D1%20%7B%20fill%3A%20%23ff7f0e%3B%20stroke%3A%20%23ff7f0e%3B%20%7D%0A%2Eparset%20%2Ecategory%2D2%20%7B%20fill%3A%20%232ca02c%3B%20stroke%3A%20%232ca02c%3B%20%7D%0A%2Eparset%20%2Ecategory%2D3%20%7B%20fill%3A%20%23d62728%3B%20stroke%3A%20%23d62728%3B%20%7D%0A%2Eparset%20%2Ecategory%2D4%20%7B%20fill%3A%20%239467bd%3B%20stroke%3A%20%239467bd%3B%20%7D%0A%2Eparset%20%2Ecategory%2D5%20%7B%20fill%3A%20%238c564b%3B%20stroke%3A%20%238c564b%3B%20%7D%0A%2Eparset%20%2Ecategory%2D6%20%7B%20fill%3A%20%23e377c2%3B%20stroke%3A%20%23e377c2%3B%20%7D%0A%2Eparset%20%2Ecategory%2D7%20%7B%20fill%3A%20%237f7f7f%3B%20stroke%3A%20%237f7f7f%3B%20%7D%0A%2Eparset%20%2Ecategory%2D8%20%7B%20fill%3A%20%23bcbd22%3B%20stroke%3A%20%23bcbd22%3B%20%7D%0A%2Eparset%20%2Ecategory%2D9%20%7B%20fill%3A%20%2317becf%3B%20stroke%3A%20%2317becf%3B%20%7D%0A%2Eparsets%2Etooltip%20%7B%0Abackground%2Dcolor%3A%20rgba%28242%2C%20242%2C%20242%2C%20%2E6%29%3B%0Aposition%3A%20absolute%3B%0Apadding%3A%205px%3B%0Aopacity%3A%201%3B%0A%7D%0A" rel="stylesheet" /><!-- --><!-- --><!-- --><!-- --></head><!-- --><body style="background-color:white;"><!-- -->
<!-- --></div><!-- -->{"x":{"data":{"A) Surveyed province":,"B) Surveyed farmer gender":,"C) Provided seed to":},"options":{"spacing":0,"tension":0.4}},"evals":,"jsHooks":}<!-- -->{"viewer":{"width":600,"height":300,"padding":15,"fill":false},"browser":{"width":600,"height":300,"padding":40,"fill":false}}<!-- --></body><!-- --></center><!-- --><center><h3>Farmer provision of seed to others in 2016-17. You can interact with the data as above.</h3></center><!-- --> Tay Ninh seems to be responsible for most of the seed supply to traders, indicating the presence of a stronger stem export network than in the other provinces. It is also interesting to note that 9% of seed supply was provided to farmers that the respondent did not know (category C). Follow-up questions suggest that farmers take advantage of the period immediately after harvest, when there is a large stem surplus, to acquire stems from others. Studying the data collected in these surveys allowed us to make a first description of the differences in seed exchange behavior of farmers in different settings. Elaborate regional flows of seed appear to be occurring between different types of actors in the seed system, including farmers, cassava root collection centers, and specialized traders. To better understand the spatial structure of the network, we then aggregated exchange data to make a map of the seed exchange network at the provincial level, providing a snapshot of seed transport across the region. In just a single season, cassava seed traveled long distances to and from the farmers in our sample. Despite a large percentage of seed exchange in each country being self-saved from the year before (47 and 64% of seed use cases in Cambodia and Vietnam, respectively), big volumes of seed still moved around the region and crossed international borders freely. There is a lot to unpack in the data, but here are five major takeaways about local seed systems from the recent publication (full text available at
this open-access link (Delaquis et al., 2018)).:
1. The cassava seed system is farmer and trader-driven and regulated through social and commercial networks in Vietnam and Cambodia, with very little ‘formal’ seed production or quality control. 2. Frequent seed exchange occurs between farmers in the same community, but re-use of the farmer's own seed supply remains the most common source of seed in both countries. 3. Volumes reaching several thousand planting stakes moved distances exceeding 300km in the study season. 4. Dedicated cassava traders have a robust informal network, and play an especially important role in cross-border transactions. 5. International movement of cassava seed is common, supplying 20% of stakes used at the national scale in Cambodia. All of the exchanges recorded went into Cambodia from neighboring countries; none went out. These findings give us new insights on how varieties, diseases, and information spread through farmer networks. Although most exchange occurs between neighbors and members of local communities, a sizeable fraction of longer distance trade links otherwise distant production areas. Rather than preventing seed movement, as intuition would suggest, international borders seem to perversely encourage it. There is a practical reason for this. Both Vietnam (Tay Ninh province) and Thailand (Nakhon Ratchasima province) have highly developed cassava processing industry hubs with dozens of factories that use cassava roots to extract starch. To continue to run at full capacity, these zones require imports of vast volumes of cassava roots, many of which are across the border in less-developed Cambodia and Laos where far fewer factories are operating. Thousands of trips back and forth with heavy trucks take place in a single season to supply these factories with roots. On the way to the factory, the trucks are full of roots. But on the way back, they have free cargo space - which can be filled with cassava stems, and sold to farmers at a profit. The quest to extend the processing season also means that factories continue to incentivize early harvest. This is great for factories since it extends their processing window. However, cassava stems have a limited shelf life, and after 3 months of standing in the field in full sun, up to 3/4 of planting stems have already died. So farmers that harvest early because of tempting factory prices end up looking off-farm for next year's seed. The results of this work are particularly timely, as a spate of seed-vectored pests and diseases (including the newly arrived cassava mosaic virus) are making inroads in cassava fields across the region. An increased understanding of seed use patterns helps us to identify key points for plant health surveillance and interventions, and to explore the potential for more ‘formal’ seed production systems to gain a foothold in Southeast Asia. Work is ongoing to document and understand the functioning of official sources of seed, like government multiplication centers and NGO or private sector sponsored activities. Evaluating the costs of seed production and understanding mechanisms of seed dissemination will help seed production systems to interface with farmer seed networks, improving access to healthy seed across the region. The full manuscript of this work is available for free at
https://www.frontiersin.org/articles/10.3389/fsufs.2018.00073/full. This research was undertaken as part of the
CGIAR Research Program on Roots, Tubers and Bananas (RTB). Funding support was provided by the Australian Centre for International Agricultural Research (ACIAR).
