Seed Cleaning

Staining pattern after tetrazolium test in monocot seeds. Numbers 1–4 are germinable seeds and numbers 5–9 are nongerminable seeds (adapted from AOSA, 2005). 1 2 3 4 5 6 7 8 9 78 Handbooks for Genebanks No. 8 Why is seed health testing important? Crops are frequently infected with a range of common seed-borne pathogens that may not be visible or easily recognized during seed collection. Seed-borne inoculums reduce storage longevity and cause poor germination or field establishment. Seed-borne inoculums also promote disease in the field, reducing the value of crops. ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

Exchange of infected seeds may allow spread of diseases and pests into new regions. Genebanks should ensure that seeds prepared for conservation are free from seed-borne diseases and pests. Common seed-borne pests and pathogens There are four main types of common organisms that are carried in seeds and affect a wide range of crops: • Fungi • Bacteria • Viruses • Insects Specific methods for detecting pathogens vary by organism and host, and specific methods are required for accurate identification of most pathogens. Methods of detecting pests and pathogens Seed-health standard Examine a representative sample of seeds for the presence of pathogens using one or more of the following methods. Usually, a sample of 400 seeds in replication of 100 seeds each is drawn for examination. Sample size can be decreased for small seed lots. If the percentage of seeds infected is greater than 5%, the seed lot can be considered unsuitable for conservation. Visual examination The simplest method to detect diseases and pests is to examine dry seeds with the naked eye or under a low-powered microscope. This method reveals freely moving insects, eggs, mites, fungal ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

fructifications like sclerotia, galls, smut balls, bacterial masses and infected plant debris. Examination of dry seeds under ultraviolet or near-ultraviolet light reveals infections of certain fungi and bacteria through emission of fluorescence. Seedling evaluation Seeds should be planted in sterilized soil in a screenhouse. Seedlings should be observed immediately after germination and any plants exhibiting virus-like symptoms such as leaf mottling, curling or yellowing should be sampled and tested for viruses (see 79 Manual of Seed Handling below). Seedlings infected with bacteria or fungi may die and should be examined further in a laboratory, and the samples should be plated for identification of the pathogen (see below). If infection is suspected but no symptoms have been observed after the ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

second true leaf has emerged, it may be necessary to carry out serological tests for latent or symptom-less infection by viruses.