Histopathology of Albugo tragopogonis on stems and petioles of sunflower

Stem lesions in sunflower caused by Albugo tragopogonis (Pers.) S.F. Gray d eveloped individually from primary infections and did not result from a sys temic infection. Cell division and callose formation were not observed, but weak lignin deposition occurred in infected tissues. Hyphae occurred inter cellularly in stems in the cortex, cambium, vascular rays, and pith. In pet ioles parenchymatous tissue was heavily colonized in contrast to lightly co lonized collenchymatous hypodermis. The middle lamellae of cells in infecte d tissue were dissolved, and cells degenerated and eventually collapsed. St em infections lead to deterioration of tissue integrity, weakening of stems , and finally to lodging of stems (breaking over).