POTENTIAL YIELD AND TOLERANCE TO VIRUS-DISEASE IN GARLIC (ALLIUM-SATIVUM L)

A field trial was used to compare 2 garlic clones, Germidour and Thermidrome, each in three different virological conditions: chronic infection by garlic mosaic virus, mechanical inoculation with garlic mosaic 4 months after planting, and healthy plants. Symptoms of chronic and artificial virus infection are stronger in Thermidrome, in which chronic and shock symptoms are different, with a secondary attack of Pyrenochaeta terrestris on roots in the 2nd instance, probably caused by a deterioration of the source/sink ratio. Measures of chlorophyll content of leaves confirm the visual observation of symptoms. The yield of bulbs is reduced by 25% for virus diseased plants of Germidour, more than 50% for Thermidrome. Two reasons explain similar yields for VC6 (the original virus-diseased clone from which Germidour was extracted by meristem culture) and for healthy Thermidrome. A paradoxical explanation of the persistence of healthy plants in the Blanc de la Drome variety may be looked for in its extreme virus-susceptibility, which is supposed to have made efficient the traditional massive selection of bulbs and cloves before planting. With more tolerant varieties, like Violet de Cadours, from which VC6 was obtained, such a massive selection was probably less efficient, with the consequence of a 100% virus infection on these varieties.