LEAF-TIP NECROSIS IN FORCED TULIPS AS A RESULT OF A ROOT DECAY CAUSED BY TRICHODERMA VIRIDE

Formerly forcing boxes were filled and covered with outside soil and plunged. During the past decade, however, growers switched to the use of peat substrates for filling the boxes and these boxes are stacked more and more in temperature-controlled rooting rooms.

In the latter planting system a much thicker root mass without any soil particles develops on the bottom of the boxes and roots grow through drainage openings into the space between the boxes. This situation easily leads to the development of a root decay caused by Botrytis cinerea and Trichoderma viride. When Trichoderma is involved the leaf tips of the forced tulips become greyish white and wither, looking as though they were poisoned. When a substance extracted from cultures of Trichoderma was injected into tulip plants, identical symptoms were observed.

Symptoms and inoculation experiments will be described and measures will be discussed that might prevent this disease. It is suggested that a toxic substance, produced by Trichoderma in the roots is transported and accumulated in the leaf tips and is responsible for the observed symptoms.

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