Investigation on host-parasite interaction between the stem nematode <em>Ditylenchus dipsaci</em> and sugar beet Beta vulgaris and their importance for development of alternative integrated management strategies

Abstract

The re-occurrence and rapid spread of D. dipaci in German sugar beet production areas enhanced the necessity for a holistic management strategy of this pathogen to secure sustainable sugar production. <br /> To evaluate sources of resistance or tolerance in available germplasms a standard screening protocol was developed. The inoculation of 14 days old sugar beet seedlings between the leaf axils proved to be the most efficient infestation procedure. Different geling agents were tested as nematode carriers. Carboxymethyl cellulose provided the highest increase of nematode penetration rates by promoting a longer penetration time frame. The developed standard inoculation protocol was used to compare different artificial screening procedures to field screening results. The highest correlation was detected between D. dipsaci rating results of heavily infested fields and the evaluation of symptoms after artificial inoculation under controlled greenhouse conditions. Therefore a reliant protocol for a high throughput screening of sugar beets against D. dipsaci was developed.<br /> Penetration time frame of D. dipsaci into sugar beets was evaluated. The highest penetration rate occurred when nematode suspension was applied when the seedlings were germinated but remained in soil. A protection of the short period between germination and emergence from ground could be protected by a nematicidal seed coating.<br /> The reproduction capability of D. dipsaci in sugar beets was investigated. Different sugar beet varieties showed significantly varying nematode reproduction. The initial nematode density at time of inoculation, ranging from 10 -200 nematodes per plant had no significant impact on symptom development 54 days after inoculation. <br /> Geostatistical analyses were used to evaluate the site specific management potential of D. dipsaci and Heterodera schachtii. The cluster size of D. dipsaci was smaller and the distribution of rot symptoms was very heterogenic. Therefore it could be concluded that site specific management is rather suitable for H. schachtii where also a high correlation between initial nematode densities and occurring yield decrease is known.