Euphytica 135: 119–128, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands. 119 Genetic variation in Zantedeschia spp. (Araceae) for resistance to soft rot caused by Erwinia carotovora subsp. carotovora Ronald C. Snijder 1 , Hae-Ryong Cho 2 , Margriet M.W.B. Hendriks 3 , Pim Lindhout 4 & Jaap M. van Tuyl 1,∗ 1 Plant Research International, Business Unit Biodiversity and Breeding, Wageningen University and Research Centre P.O. Box 16, 6700 AA Wageningen, The Netherlands; 2 National Horticultural Research Institute-Rural De- velopment Administration, 475 Imok-Dong, Jangan-Gu, Suwon, Republic of South Korea; 3 Biometris, Wageningen University and Research Centre, P.O. Box 100, 6700 AC Wageningen, The Netherlands; 4 Laboratory of Plant Breeding, Graduate School for Experimental Plant Sciences, Wageningen University and Research Centre P.O. Box 386, 6700 AJ Wageningen, The Netherlands; ( ∗ author for correspondence; e-mail: jaap.vantuyl@wur.nl) Received 24 March 2003; accepted 13 October 2003 Key words: Aestivae, aggressiveness, breeding, IRREML, leaf disk test, Pectobacterium carotovorum subsp. carotovorum Summary Bacterial soft rot caused by Erwinia carotovora subsp. carotovora is a major disease in Zantedeschia spp., partic- ularly in cultivars from the section Aestivae. The disease can partially be controlled by cultivation measures, so a combination with resistant cultivars could effectively protect the crop. However, resistant commercial Aestivae cultivars are not available yet. By means of a recently developed non-destructive resistance test, variation in aggressiveness was observed among five isolates of Erwinia carotovora subsp. carotovora without interactions between the isolates and three Zantedeschia accessions. Within eleven accessions of Z. aethiopica, variation was observed from almost complete to moderate resistance, while the Z. odorata accession was susceptible. All 21 Aestivae cultivars were susceptible. Within the Aestivae species, Z. elliotiana and Z. pentlandii were also suscept- ible, but within twelve accessions of Z. albomaculata, as well as in six accessions of Z. rehmannii, variation was found from susceptible to moderately resistant. Hence, new sources of resistance were identified that show good potentials for resistance breeding. Abbreviations: GLMM – Generalised Linear Mixed Model; IRREML – Iterative Reweighted Residual Maximum Likelihood; M – index of macerated leaf disk area; PRI – Plant Research International Introduction The genus Zantedeschia (Araceae), consists of eight species in two sections, all from southern Africa. Sec- tion Zantedeschia is characterised by the presence of a rhizomatous tuber and consists of the species Z. ae- thiopica and Z. odorata (Singh et al., 1996). Species of section Aestivae are characterised by the pres- ence of a discoid tuber (Singh et al., 1996), referred to as a ‘root tuber’ by Wright & Burge (2000). Z. odorata and species from the section Aestivae require a dormancy period, in contrast to Z. aethiopica (Fun- nell, 1993). Most cultivars have been developed from crosses between species of section Aestivae, mainly Z. albomaculata, Z. elliotiana, Z. rehmannii and Z. pentlandii (Funnell, 1993). Bacterial soft rot caused by Erwinia carotovora subsp. carotovora occurs world wide in many crops. This soilborne facultative anaerobic pathogen causes maceration and rotting of parenchymatous tissue of all plant organs, eventually resulting in plant death (Pérombelon & Kelman, 1980; Wright, 1998). It is an important disease in Zantedeschia spp. and the ma- jor disease in cultivars of section Aestivae (Corr et