Lack of Association between Fusarium Foot Rot and Head Blight Resistance in Winter Rye

Abstract

Foot rot and head blight caused by Fusarium culmorum (W.G. Sm.) Sacc. may lead to considerable loss of yield and grain quality in winter rye (Secale cereale L.). Breeding for resistance to the two diseases would be facilitated if the same resistance mechanisms were involved. The purpose of this study was to estimate the genetic correlation between the resistance to the two diseases in advanced winter rye breeding materials. Twenty self‐fertile inbred lines were grown at two locations in South Germany in 1992, 1993, and 1994 (six environments). Lines were arranged in three adjacent treatment blocks: no inoculation, inoculation for foot rot, and inoculation for head blight. Disease severity was rated on a 1‐to‐9 scale for foot rot and head blight. Besides the foot rot and head blight rating scale, ELISA (enzyme‐linked immunosorbent assay) was used to quantify the amount of Fusarium protein within stem issue from the foot rot treatment and relative grain weight was measured from the head blight treatment. In all but one environment, F. culmorum was re‐isolated from diseased stems at high percentages (≥90%). Disease severity was moderate for foot rot and head blight rating at all environments. Mean ELISA absorbance was 0.55 and mean relative grain weight 77.4%. Significant genotypic variation existed for all resistance traits. Broad‐sense heritabilities, calculated on an entry‐mean basis, were high for foot rot and head blight rating (h2 ≈ 0.8) and somewhat lower for ELISA absorbance and relative grain weight (h2 ≈ 0.5–0.6). No significant correlation was found between the resistances to foot rot and head blight. This was confirmed by a highly significant (P = 0.01) genotype‐plant organ interaction. Thus, resistance mechanisms most likely differ for the two diseases. Resistance selection requires separate multi‐environmental screening tests for F. culmorum foot rot and head blight.