&lt;i&gt;In vitro &lt;/i&gt;technique for selecting onion for white rot disease resistance

A.M Osman Sayed,T Abdel-Rahem Abdel-Rahem,Z Ahmed Kasem,A Mohamed Abdel-Rahem

doi:10.4314/acsj.v24i3.7

Abstract

In vitro selection is one of the most effective and efficient techniques for plant improvement. This is due to its ability to isolate plants with the desired character(s), either by applying a selection agent on the culture media to drive the selection of somaclones with the required character(s), or by establishing particular conditions that change in the genomes of somaclones toward the required character. The objective of this study was to identify a suitable protocol for in vitro selection of Allium white rot disease ( Sclerotium cepivorum ) tolerance in commercial Egyptian onion varieties, namely Giza 20, Giza 6 and Beheri Red. Oxalic acid (OA), the phytotoxin produced by Sclerotium cepivorum , was used as the selective agent. Seeds of the three Egyptian varieties were germinated on four concentrations (0.0, 0.02, 0.2, 2 and 20 mM) of Oxalic acid. Among the tested cultivars, Beheri Red had the highest germination frequency (52%) at all concentrations tested, followed by Giza 20 (42.6%), and Giza 6 at (32%). Cotyledon explants from the varieties were cultured on toxic MS BDK medium, supplemented with 0, 3, 6 and 12 mM OA. The survival of calli on MS BDK free toxic medium was 70.7% for all tested cultivars; however, MS BDK -stressed medium, with 3 mM OA reduced the viable calli to 42.1%. The highest OA concentration (12 mM) completely inhibited calli induction from cotyledons explants. A medium supplement with 3 mM OA retarded 80% of calli growth. Among 156 tested calli of Beheri Red, only 23 calli (14.7%) survived on toxic medium for 45 days. Similarly, there was 15.6% survival for Giza 20 calli, while 40.1% of the Giza 6 calli survived. Plantlets were regenerated from surviving calli and transplanted onto ex vitro, and formed bulb after acclimatisation. Key Words : Allium cepa, oxalic acid, Sclerotium cepivorum

Highlights

Onion (Allium cepa L.) is one of the most important vegetable crops in Sub-Saharan Africa
Seeds of three local commercial onion (Allium cepa L.) cultivars, Giza 20, Giza 6, Beheri Red, were kindly provided by the Seds Agriculture Research Station, Agriculture Research Center (ARC), Ministry of Agriculture, Seds, Egypt. These cultivars are sensitive to Allium white rot (Sclerotium cepivorum) disease in onions (Davis et al 2007)
There were significant differences between callus initiation rates for each of the different concentrations of Oxalic acid (OA); but no genotypic differences were observed for the three Egyptian onion commercial cultivars (Table 2)

Summary

Introduction

Onion (Allium cepa L.) is one of the most important vegetable crops in Sub-Saharan Africa. Onion is susceptible to several plant pathogens including soil-born fungi; such as molds, fungi, bacteria and nematodes (Davis et al 2007; Francisco et al, 2011). The sclerotia remain in the soil in the absence of host plants, for more than 20 years. They begin to germinate only in the presence of Allium-specific root exudates, making the disease highly specific to Allium species. The sclerotia penetrate their host plant causing AWR disease (Maude, 2006; Davis et al, 2007)

Objectives

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Results