Relation Between Foliar Symptoms and Systemic Advance ofCephalosporium gramineumDuring Winter Wheat Development

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Abstract
Systemic spread of the vascular pathogen, C. gramineum, was characterized relative to anatomical and developmental features of its winter wheat (T. aestivum) host. Pathogen restriction was associated with xylem maturation gradients between internodes, within nodes, and within leaves. Restriction of symptom development also was attributed to increased gelation and gummosis within the xylem and/or to inhibition of fungal sporulation. All evidence suggested that this pathogen is incapable of penetrating living cells at any time during the disease cycle. The number and pattern of vascular bundles in different winter wheat cultivars and the temporal association between pathogen colonization and symptom induction formed the basis for a disease index rating system. Both the movement and distribution of C. gramineum and the disease index rating system have practical implications in a germplasm development program. The former emphasizes the need to separate rate of disease development from rate of host development in evaulating winter wheat genotypes. The latter provides a valuable tool for monitoring symptom expression within and among plants of different genotypes.