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Genetic variation in susceptibility of maize to Rhizoctonia solani (AG 2-2IIIB) - symptoms and damage under field conditions in Germany

  • Autor/in: Buddemeyer, J., B. Pfähler, J. Petersen, B. Märländer
  • Jahr: 2004
  • Zeitschrift: Z. PflKrankh. PflSchutz 111
  • Seite/n: 521-533
  • Stichworte: Rhizoctonia solani maize crown and brace root rot Rhizoctonia index

Abstract

In Germany, an economic production of sugar beet is increasingly limited by the soil-borne fungus R. solani, anastomosis group (AG) 2-2IIIB, which causes sugar beet root and crown rot. The occurrence of R. solani is influenced by environmental conditions. The main areas of Rhizoctonia root rot incidence are characterized by crop rotations with sugar beet and maize. Moreover, the severity of sugar beet root and crown rot is related to the frequency of sugar beet and maize in crop rotations. Sugar beet root and crown rot occurs at a disproportional high frequency on farms with a high cropping frequency of both host plants. Since 2001, patch-wise lodging in maize has been reported, but causes to date were unknown. The study reported here was conducted to investigate the damage that AG 2-2IIIB caused to maize under German growing conditions. Rhizoctonia–induced symptoms were described and a variation in Rhizoctonia susceptibility of different maize cultivars was investigated. Therefore, in greenhouse and field trials, maize cultivars were infected with R. solani AG 2-2IIIB isolated from sugar beet. Inoculation of maize with R. solani caused round to elliptical, yellow to brown or black lesions partly with dry lesions or strangling of crown and brace roots. Depending on the disease severity, crown roots were completely rotten and affected plants lodged. Some heavily infected plants expressed small medallion lesions on the shoot. A nine-class root disease index was developed to describe the disease severity on crown roots and shoot basis of maize. Shoot fresh matter and grain yield of infested plants compared to healthy plants were reduced up to 37 and 12 %, respectively. Significant differences in susceptibility of cultivars to the pathogen were observed. The results show that R. solani AG 2-2IIIB caused crown and brace root rot of maize under German growing conditions. Differences in sensitivity of maize hybrids to the pathogen can quickly and reliably be determined by assessing the amount of damaged crown and brace roots with the index described in this study.
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