Effects of infection by Septoria nodorum at different development stages of wheat on the level of production

1. In pot trials over three vegetation periods with spring wheat (var. 'Famos'), effects of a singular infection by Septoria nodorum (by excluding secondary infections), at the growth stages EC 13, 37, 39, 59 and 69, on the biomass (dry weight) production, number of kernels/ear, single ear yield and 1000 kernel weight were investigated. At stages EC 59 and 69, inoculation was done separately for leaves and heads. Manifestation of symptoms was evaluated up to full maturity separately for each leaf insertion. 2. At high densities of inoculum (10(6)/spores/ml), disease rates after inoculation at EC 13 were only 5 per cent, at EC 322048 25 up to 70 per cent, at EC 39 to 69 from 50 to 100 per cent. Production of biomass was not affected by inoculation at EC 13. Highest decreases of biomass after inoculation were: EC 32 24 per cent, EC 39 43 per cent, EC 59 52 per cent, EC 69 40 per cent. 3. Single ear yields were strongly reduced after inoculation at EC 32 by 23 per cent, at EC 39 by 52 per cent, at EC 59 by 66 per cent, at EC 69 by 67 per cent. At earlier stages, only the number of kernels/ear was negatively affected, lateron also the kernel weight. Leaf infections had stronger effects than infection of the ear. 4. By applying various densities of inoculum (10(6), 3 x 10(5), 10(5), 5 x 10(4), 10(4), 10(3) spores/ml) at the stages EC 32 up to 69, infection rates similar to practical conditions could be obtained. Disease rates in single leaf insertions were correlated with the decrease of plant resistance in the course of their development. Production of biomass was reduced even by the smallest density of inoculum (EC 32 14 per cent, EC 39 23 per cent, EC 59 23 per cent, EC 69 20 per cent), the single ear yield was lowered by 13 to 22 per cent. Increasing densities of inoculum resulted in higher losses. Decreases in production could be observed with kernels, glumes plus spindles and the upper four leaves plus parts of the culm. In all cases, an earlier onset of senescence could be observed as compared to control plants. 5. The results are discussed in relation to the importance of Septoria infections for yield production under field conditions and the general plant develop