Sclerotial formation and strand growth of Phymatotrichopsis omnivora in minirhizotrons planted with cotton at different soil water potentials
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In situ strand growth and sclerotium formation of Phymatotrichopsis omnivora were observed in minirhizotrons using a microvideo camera. Strand growth was greater in soils subject to decreasing levels of soil matric potential (high water stress) compared with a continuously wet treatment. Intermediate levels of water stress (- 0-5 to -0.9 MPa) resulted in less strand growth than either the dry or wet treatments. In all treatments strand growth increased to a maximum within 10 days of inoculum placement in soil but then declined to approach an apparent steady-state value. The effects of soil matric potential on sclerotium formation were apparent when barley seeds were sown in the experimental units 3 weeks after the experiment had begun, permitting differential water cycling patterns to be obtained. Sclerotia were recovered in larger numbers from experimental units in which high water potentials (>-0.2 MPa) occurred 2 weeks prior to and following the death of host plants.