Comparing infection and colonisation of Puccinia graminis in barley and wheat

Abstract

Barley, host to the wheat and rye attacking forms of the stem rust pathogen, Puccinia graminis (Pg), is considered inherently more resistant to Pg than wheat. To investigate whether this enhanced basal defence is associated with early infection or colonisation processes, adult plants of selected barley and wheat entries were inoculated with Pg f. sp. tritici (Pgt) races BNGSC and PTKST, and Pg f. sp. secalis (Pgs) isolate UVPgs1. Flag leaf sheaths on the last stem internode were sampled for analysis. Using scanning electron microscopy and epidermal stripping, early Pg infection structure development was compared between barley and wheat. Sub-stomatal vesicle appearance and production of haustorial mother cells were similar at 24 and 48 h post inoculation (hpi), respectively. Significant variation occurred among host entries (P ≤ 0.01) for colony size and fungal biomass at 120 hpi. Differences between the Pgt races and the Pgs isolate as well as the host entry-Pg isolate interaction proved insignificant (P ≥ 0.05). The period between 120 and 240 hpi may hold some explanation for the perceived lower stem rust receptivity in barley, since a steep increase in accumulated fungal biomass observed in the susceptible wheat Line 37 − 07 was not seen in the susceptible barley entries at the same time interval.