Influence of different levels of resistance or tolerance in sugar beet cultivars on complex interactions between Heterodera schachtii and Rhizoctonia solani

Abstract

The existence of synergistic interactions between the beet cyst nematode Heterodera schachtii and Rhizoctonia crown and root rot of Rhizoctonia solani (Anastomosis Group 2-2IIIB) in concomitant treatments was investigated on susceptible, tolerant and resistant sugar beet varieties. The influence of sequential inoculation of the two organisms was also analysed. Leaf reflectance measurements were made with a hyperspectral spectroradiometer to monitor symptom development of the concomitant disease interaction as compared with the effects of the disease organisms present singly in both studies. The results demonstrated that a significant interaction exists between H. schachtii and R. solani on sugar beet. However, the three susceptible cultivars responded differently to the concomitant treatments. The susceptible cultivar showed synergistic levels of damage when simultaneously inoculated with H. schachtii and R. solani . Synergistic effects were also detected in the concomitant treatments on the R. solani tolerant cultivar. Conversely, damage was lower on the H. schachtii resistant cultivar in the concomitant treatments. Heterodera schachtii reproduction was negatively affected and R. solani development positively influenced on the susceptible and tolerant cultivars in the concomitant treatments when compared with the individual controls. Sequential inoculation of sugar beet seedlings caused higher levels of disease when compared with the two organisms inoculated singly. Leaf reflectance gave reproduced results in the detection of Rhizoctonia crown and root rot disease development. Normalised Difference Vegetation Index (NDVI) values of leaf reflectance showed high correlations to plant and visual disease symptom rating variables over the duration of the experiments. The NDVI allowed disease severity detection without damage to the plant. The results demonstrated that hyperspectral reflectance can be used effectively to monitor aetiopathology of R. solani and may be an effective tool for early detection of Rhizoctonia crown of root rot symptoms in the field, in breeding programme tests and for the early prediction of yield impact.