Evidence that wheat cultivars differ in their ability to build up inoculum of the take‐all fungus,Gaeumannomyces graminis var. tritici,under a first wheat crop

The effect of wheat cultivar on the build‐up of take‐all inoculum during a first wheat crop was measured after harvest using a soil core bioassay in field experiments over five growing seasons (2003–2008). Cultivar differences in individual years were explored by analysis of variance and a cross‐season Residual Maximum Likelihood (REML) variance components analysis was used to compare differences in those cultivars present in all years. Differences between cultivars in the build‐up of inoculum were close to or at significance in two of the five trial years (2004 P < 0·05; 2006 P < 0·07), and current commercially listed cultivars were represented at both extremes of the range. In 2007 and 2008, when environmental conditions were most favourable for inoculum build‐up, differences were not significant (P < 0·3). In 2005 the presence of Phialophora spp. at the trial site restricted the build‐up of take‐all inoculum under all cultivars. The cross season REML variance components analysis detected significant differences (range: 3·4–47·8% roots infected in the soil core bioassay; P < 0·01) between the nine cultivars present in all years (excluding 2005). This is the first evidence of relatively consistent differences between hexaploid wheat cultivars in their interactions with the take‐all fungus, and this could give an indication of those cultivars that could be grown as a first wheat crop, in order to reduce the risk of damaging take‐all in a second wheat crop. This phenomenon has been named the take‐all inoculum build‐up (TAB) trait.