Colonization of Durum Wheat (Triticum turgidum L. var. durum) Culms Exhibiting Premature Senescence (Dead Heads) Associated with Fusarium pseudograminearum Crown Rot.

Fusarium crown rot is a significant disease of durum wheat (Triticum turgidum L. var. durum), which exhibits high levels of disease susceptibility. The most extreme symptom of crown rot is a prematurely senescing culm that typically fails to set grain. Individual crown rot-affected durum wheat plants displaying both nonsenescent and prematurely senescent culms were harvested to compare visual discoloration, Fusarium pseudograminearum biomass, and vascular colonization in culm sections sampled at three different heights above the crown. Field samples of EGA Bellaroi were collected at Wellcamp, QLD, in 2011, 2012, 2013, and 2014, and of Hyperno at Narrabri, NSW, in 2014. Prematurely senescent culms exhibited greater visual discoloration, F. pseudograminearum biomass, and vascular colonization than nonsenescent culms in each year they were examined. The extent of these differences varied between environments and timing of collection in each year. Vascular colonization initially occurred in xylem vessels and spread into phloem tissues as disease severity increased. The increased presence of hyphae in vascular bundles of prematurely senescing culms provides strong evidence for the hypothesis that restriction of water and nutrient movement in a diseased culm is a key factor in crown rot severity.