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

Abstract

Nematology , 2011, Vol. 13(3), 319-332 Influence of different levels of resistance or tolerance in sugar beet cultivars on complex interactions between Heterodera schachtii and Rhizoctonia solani Christian H ILLNHÜTTER ∗ , Richard A. S I KO R A and Erich-Christian O ERKE Institute of Crop Science and Resource Conservation (INRES) – Phytomedicine, Rheinische Friedrich-Wilhelms-Universität Bonn, Nussallee 9, 53115 Bonn, Germany Received: 12 March 2010; revised: 23 June 2010 Accepted for publication: 24 June 2010 Summary – 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. Keywords – hyperspectral reflectance, interrelationship, NDVI, sequential inoculation, synergy. The beet cyst nematode, Heterodera schachtii (Schmidt), is a sedentary endoparasite and an important pest on sugar beet, Beta vulgaris . Juveniles penetrate be- hind the lateral root tips, which become damaged, and ei- ther terminate growth or die, often because of secondary fungal infections. The formation of giant cells in the vas- cular system disrupts normal uptake of nutrients and water and results in reduced growth and yield. After penetration, compensatory secondary roots are produced that results in the typical ‘bearded’ root symptom. Nematode infec- tion results in reduced leaf growth, branched tap roots and overall beet deformity. Infested plants often wilt late in the growing season especially when exposed to heat and water stress conditions. Symptoms caused by H. schachtii ∗ Corresponding author, e-mail: christian.hillnhuetter@gmx.de in the field are manifest as patches that expand slowly in the direction of mechanical cultivation (Petherbridge & Jones, 1944). Rhizoctonia crown and root rot (RCRR) is caused by the soil-borne fungus Rhizoctonia solani (Kühn), anas- tomosis group (AG) 2-2IIIB (teleomorph Thanatephorus cucumeris (Frank) Donk) (Zens et al. , 2002), and is most visible on plants later in the growing season. Initial symp- toms are black lesions on petioles in contact with the soil surface (Richards, 1921; Leach & Garber, 1970). Rotting progresses from the petioles to the crown and then down into the beet and lateral roots. Above-ground symptoms include wilting and the formation of a rosette of yellowing and dying leaves on the soil surface (Herr, 1996). Symp- © Koninklijke Brill NV, Leiden, 2011 DOI:10.1163/138855410X519398 Also available online - www.brill.nl/nemy 319

Plant phenotyping relevance

サトウダイコンの病害症状を非破壊のハイパースペクトル反射で追跡し、NDVIと目視症状・植物形質との相関や再現性を評価しており、病害表現型の取得法が実質的に検証されている。

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