Influence of the attack by major causal agents of root and lower stem rot on structural elements of wheat yield

Tzenko Vatchev, Ivo Yanashkov

Abstract: The present study evaluated the effect of individual or mixed infections by five major soil-inhabiting fungal pathogens - Fusarium culmorum, F. graminearum, F. oxysporum, Drechslera sorokiniana and Rhizoctonia solani on structural elements of wheat (c. Laska 5) yield. Initially, all infections leaded to pre-emergence decay of seeds and post-emergence dаmping-off of wheat seedlings. In later phenological phases, the highest disease severity indices were observed on plants inoculated with F. culmorum and the five pathogens concomitantly – 3.6 and 3.8, respectively, while the non-inoculated control plants remained visually healthy. Recorded disease indices resulting from single infections with the other pathogens varied between 2.9 and 1.6. The results of the study showed a significant (P≤0.001) reduction in both structural elements of the yield from diseased wheat plants as compared to those from the non-inoculated control plants. Thus, the longest roots exhibited non-inoculated control plants (20.4 cm) and the shortest roots had the plants inoculated with F. culmorum and the mixture of the five pathogens – 12.1 and 12.2 cm, respectively. In these two treatments, the most significant reductions were recorded in the relative rooth weight (0.31g and 0.35 g) and in the absolute root weight (2.5 g and 2.6 g), while in the uninoculated control these parameters were 0.76 g and 3.7 g, respectively. The length and weight of the roots in the other treatments also showed significantly lower values compared to the control (P≤0.001). Plants inoculated with F. culmorum and mixed inoculum formed the lowest stems - 52.2 cm and 52.4 cm, respectively, significantly lower (P≤0.001) than the stems of non-inoculated plants (84.4 cm). The diseases caused by F. culmorum and D. sorokiniana were associated with formation of the lowest number of leaves – 3.6 per plant. The numbers of leaves in the other treatments with inoculations were between 4.0 and 5.2 per plant and generally lower as compared to the control (5.5 leaves). The least number of spikes – 6.2 per plant, formed the plants inoculated with mixed inoculum of the five pathogens, as well as in the treatment with F. graminearum (10.2). The single infections with F. oxysporum, D. sorokiniana, and R. solani leaded to no significant reduction of this element as compared to the number of spices formed on a single uninoculated plant – 14.2. The smallest spike length had the plants inoculated with F. culmorum (3.2 cm), followed by the treatments with mixed inoculum of the five fungal species (4.0 cm), F. graminearum (4.1 cm), D. sorokiniana (5.0 cm.), R. solani (5.0 cm) and F. oxysporum (5.2 cm); the largest was the spike length of plants in the control treatment without pathogen inoculation. Significant (P≤0.001) reductions in number of grains per spike were found in all treatments with inoculations. The most expressive was this reduction in plants inoculated with F. culmorum (17.9), while the control plants had the highest number of grains per spike – 31.2. With regard to the structural elements of yield, the mass of 1000 grains and hectoliter weight of grain yield, most pronounced losses were found in the mixed infection – 38.5 g and 65.0 kg, respectively and in the treatment with a single inoculum of F. culmorum - 38.8 g and 64.4 kg, respectively. Significantly reduced values of these two parameters were observed in all other inoculum treatments (42.4-45.2 g and 64.4-78.1 kg) compared to the control (48.1 g and 82.7 kg, respectively). The results presented herewith clearly demonstrate that all the soilborne fungal pathogens included in the study cause significant reductions in structural elements of wheat yield. In order to minimize the yield losses in wheat fields, an integrated disease control management program, effective against the whole complex of root and lower stem rot causal agents should be developed and put to practice.

Keywords: soilborne fungal pathogens; wheat; yield structural elements

Date published: 2019-01-16