Limited growth and development of P. striiformis f. sp . tritici ( Pst ). (A) Frequencies of each stage of Pst development on broad bean compared with wheat at 48 hpi. SP, urediniospore; GT, germ tube; LS-GT, germ tube locating a stomate; IH, infection hypha; H, haustorium. GT/SP, percentage of the urediniospores producing germ tubes (GT) among total urediniospores (SP); LS-GT/GT, percentage of germ tubes locating stomata (LS-GT) among all germ tubes (GT); IH/LS-GT, percentage of germ tubes locating stomata (LS-GT), successfully penetrating them and forming infection hypha (IH); H/IH, percentage of haustoria (H) formation among all infection hyphae (IH). (B) Linear length of infection hyphae (syn. colony length) (from the substomatal vesicle to the apex of the longest infection hypha), and numbers of hyphal branches, haustorium mother cells (HMC) and haustoria (H) formed per infection units measured at continuous time points after inoculation. Linear length of infection hyphae is the left Y-axis; numbers of hyphal branching, haustorium mother cells (HMC) and haustoria (H) are indicated by the right Y-axis. Mean values from three independent replications. Vertical bars represent the standard deviations.