36th International Carrot Conference Abstract

Black rot caused by Alternaria radicina in coloured carrots (Daucus carota L.)

R. Krämer, T. Nothnagel and D. Ulrich¹

Institute for Breeding Research on Horticultural and Fruit Crops, ¹Institute for Ecological Chemistry, Plant Analysis and Stored Product Protection, Julius Kühn-Institute, Federal Research Centre for Cultivated Plants, Erwin-Baur-Strasse 27, 06484 Quedlinburg, Germany

In recent times coloured carrots have received more attention in terms of a healthy nutrition because of their constitutional substances of content such as carotenoids. Therefore breeding research on coloured carrots is directed to improving disease resistance to major pathogens such as black rot disease caused by Alternaria radicina.

The objective of this study was to analyse the resistance level of carrot breeding lines to A. radicina using bioassays with root slices and detached petioles assessed for their response to a monoconidial isolate of A. radicina. Two approaches were carried out: one with field-grown material directly after harvest and after cold storage four months later, the other one with hundred-day old glasshouse-grown material.

Black rot symptoms on root slices and petioles were quantified with the digital image analysis system Scanalyser (LemnaTec, Germany) or in case of purple carrots with the image analysis software Assess 2.0 (Lamari, Canada). In the bioassays with petioles, additionally, a DAS-ELISA (Double-Antibody Sandwich Enzyme-Linked Immunosorbent Assay) with polyclonal antibodies (Julius Kühn-Institute) was used to quantify A. radicina.

More than forty coloured cultivars and breeding lines were evaluated. The resistance level was calculated as percentage of black rot symptoms on root slices and petioles, respectively. Thus screenings of fresh harvested root material revealed the lowest level of resistance among the red carrots (48-72%) and the highest among the purple ones (5-20%). The yellow carrots differed most in their response to A. radicina and showed a relatively high level of both resistance (21%) and susceptibility (83%). Percentage of black rot symptoms on white carrots varied from 22-69% and on the orange ones from 27-69%. The post storage screenings revealed a distinct effect of cold storage on the resistance level to A. radicina. Particularly in white and orange carrot accessions disease severity increased significantly up to 30% through cold storage.

Results in petiole bioassays with orange and purple carrots confirmed differences in disease severity between colour groups. Petioles from purple carrots revealed a lower relative concentration of A. radicina in ELISA. On root slices of purple carrots fungal growth was apparently less than in orange ones as it could be demonstrated by histological analysis.

The differences in resistance level of carrot lines will be compared with the profile of volatile compounds.

In coloured carrots different levels of resistance to A. radicina were identified. Especially the purple carrots revealed a comparatively high level of resistance. Analysis of resistance to A. radicina as an essential part of our pre-breeding programme will be presented.

Last updated Thursday, 25-Jul-2013 11:51:37 CDT