Sclerotial formation and strand growth of Phymatotrichopsis omnivora in minirhizotrons planted with cotton at different soil water potentials

Abstract

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.