An Ascomycete fungus that can cause severe disease on a wide range of crops, and is characterised by the formation of black sclerotia. The disease if often worse under wet conditions, such as water-logging or continuing heavy rain. Sclerotium
An over-wintering body of that is produced by some Ascomycetes. Sclerotia are usually visible to the naked eye and may be up to a centimetre long. They have a black surface but are usually white inside. They germinate to produce an apothecium lined with asci. (Plural: sclerotia). Screening
An essential step in population breeding. A large heterogeneous population is screened to find the best individuals that are to become the parents of the next generation. When breeding for horizontal resistance, the best approach is to let the locally important plant parasites do much of the screening by spoiling or killing all the susceptible individuals. The holistic approach is to screen for high yield, on the basis that only resistant plants can yield well. All measurements should be relative. That is, only the highest yielding plants are kept, regardless of how poor their yield may be in commercial terms. Screening overkill
When screening a large population for horizontal resistance, there is a danger, in the early breeding cycles, that every individual will be killed and the entire breeding population lost. This overkill can be prevented by using crop protection chemicals late in the season to ensure that the least susceptible plants produce a few seeds. If the breeding is being conducted on an organic farm, where crop protection chemicals cannot be used, it may be preferable to rent some land on a conventional farm for these early breeding cycles.
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