Chapter 8. MLN pathogen-free commercial seed production: standard operating procedures

The preceding chapters have shown the extent to which viruses that cause MLN can be transmitted through contaminated maize seeds, thereby contributing to the spread of MLN disease within and across countries. Formal and informal seed movement locally and across borders plays a significant role in the spread of transboundary diseases like MLN. Therefore, diagnostic tests for MLN viruses at various stages during seed production and before shipment of seeds is crucial. Quality seed production leading to regulator’s approval as certified seed is key for effective management of MCMV/MLN. Even if a 0.01% infection in a seed field of about 55,000 plants per hectare is missed, this would mean about 5-6 infected plants, which then become sources for further transmission by insect-vectors. If this infected seed production field is harvested, and the seeds find their way to the farmers’ fields, in the presence of vectors like thrips and aphids, not only the entire field but also the village itself will be at the risk of devastation by MLN (especially when the farmers plant MLN-susceptible varieties). Therefore, MLN threshold levels in commercial maize seed production fields during field inspections should be close to zero (≤1% infection) from the perspective of infected plants. Fields with higher infection levels should NOT be certified for sale of seed to the farmers. At the seed level, the stringency level should be even higher: zero tolerance for any contaminated seed.