April 28, 2006
From: ProMED-mail<promed@promedmail.org>
Source: Society for Plant Pathology, New Disease Reports, Vol. 13 [edited] <http://www.bspp.org.uk/ndr/july2006/2006-26.asp>


First report of Verticillium wilt, race 2 on tomato in Tunisia
M. Daami-Remadi1, H. Jabnoun-Khiareddine2*, D.J. Barbara3, A. Fakher2 and M. El Mahjoub2. 1 National Institute of Agronomic Research of Tunisia, PRRDA-CE Chott-Mariem, 4042 Sousse, Tunisia. 2 Horticultural High School and Breeding of Chott-Mariem, 4042 Sousse, Tunisia. 3 Warwick HRI, Wellesbourne, Warwickshire, CV35 9EF, UK *<jkhayfa@yahoo.fr>

Accepted for publication 18 Apr 2006

Vascular wilt diseases have recently become a serious problem on tomato (_Lycopersicon esculentum_) throughout the Tunisian Sahel. Since 2002, plants of cv. 'Colibri' with symptoms characteristic of Verticillium infection (wilting, yellowing, stunting and dark brown vascular discoloration) have been seen in many greenhouses in the Chott Mariem region (Fig. 1).

Isolates from diseased plants were identified as _Verticillium dahliae_ on the basis of microsclerotium production (Hawksworth & Talboys, 1970). The cultivar 'Colibri' carries a single dominant gene (Ve) conferring resistance to race 1 of _V. dahliae_ (Schaible et al., 1951). This resistance has been effective for over 20 years. 
Wilt caused by _V. dahliae_ has also been confirmed in several other resistant cultivars (e.g. Amel, Cenkara, Rio Grande) (Fig.2). A total of 51 Tunisian isolates were tested to determine their race, with Canadian and Israeli race 1 and 2 isolates (one each) were included as controls.
Conidial suspensions of 107 conidia per ml were used to inoculate plants of the cultivars 'Ventura' and 'Sun 6200' (susceptible to both races), and 'Rio Grande', 'Colibri' an 'Naya' (resistant to race 1), at the 2-leaf stage by root dipping. Seedlings were replanted into a sterile 2:1 mixture of peat/perlite (v/v) and maintained in a growth chamber at 23 ± 3deg C.
Equal numbers of plants of each cultivar were dipped into water as controls. The experimental design was a completely randomized type with ten replicates (pots). Tests were conducted twice.
Susceptible plants developed typical symptoms of wilt as above, starting 2-3 weeks after inoculation, followed by plant death. Race 1 isolates gave either no or only very mild symptoms in the resistant cultivars. Control plants showed no symptoms. In cultivars where infection occurred, most plants developed typical symptoms. _V. dahliae_ was recovered by plating from all plants with symptoms. Based on the differential reactions of the 5 cultivars, 10 isolates were classified as race 1 and 41 as race 2.

Figure 1: Yellowing, wilting and withering of leaves on a resistant (i.e. carrying the Ve gene) tomato naturally infected by _Verticillium dahliae_ <http://www.bspp.org.uk/ndr/july2006/2006-26-1.jpg>

Figure 2: Symptoms of Verticillium wilt in naturally infected resistant tomato plants from Chott Mariem, Tunisia: whole plants with desiccated leaves <http://www.bspp.org.uk/ndr/july2006/2006-26-2.jpg>

The appearance of _V. dahliae_ race 2 in tomatoes in Tunisia poses a major threat to this crop, particularly in protected cultivation where no rotations are used and the absence of soil disinfection favours the build-up of soil-borne inoculum. _V. dahliae_ race 2 has been reported from southern Europe, North and South America and North and South Africa (Pegg & Brady, 2002) but this is the first report from Tunisia.

Acknowledgements

The authors would like to thank Aymen Youssef for hi excellent technical assistance.

References

Hawksworth DL, Talboys PW, 1970. Verticillium albo-atrum. CMI Descriptions of Pathogenic Fungi and Bacteria. No. 255. Wallingford, UK: CABI Publishing.

Pegg GF, Brady BL, 2002. Verticillium wilts. Wallingford, UK: CABI Publishing.

Schaible L, Cannon OS, Waddoups B, 1951.
Inheritance of resistance to Verticillium wilt in a tomato cross. Phytopathology 41, 986-990.

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[The crop plant tomato, _Lycopersicon esculentum_, develops symptoms of the disease Verticillium wilt, when infected by the fungus _Verticillium dahliae_. Once a plant is infected, part of the leaflet lamina wilts in the shape of a "V". This is accompanied by inner vein yellowing, which begins unilaterally and is, in turn, followed by a desiccation of the leaves at the base of the plant. The vessels are coloured light brown or light gray. The affected plants do not die. Inoculum source is normally from resting structures of the fungus (microsclerotia) in infested soil.

This article describes the 1st detection of race 2 of the fungus in Tunisia. Race 1 is common in Tunisia, and the local tomato varieties grown under protected structures (screenhouses/greenhouses) while resistant to race 1, develop Verticillium wilt when attacked by race 2. Race 2 of _V. dahliae_, virulent on cultivars with the Ve gene that provides resistance to Race 1, was first detected in 1957 and later reported in North and South America, Europe, Africa and Australia. Until recently [2005] screenings of tomato germplasm have not revealed a reliable source of resistance to race 2, but a factor conferring resistance in the Veda line has been mobilized by conventional breeding and is dominantly inherited. Grafting of susceptible scions onto resistant rootstocks is one possible approach to managing this soilborne disease when soil sterilization/disinfection is not acceptable or practiced, which seems to be the case in Tunisia. Fungicidal treatment of infected plants is largely ineffective against Verticillium wilt of tomatoes.

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Map:
Tunisia: <http://www.merriam-webster.com/cgi-bin/nytmaps.pl?tunisia>
Worldwide distribution of V. dahliae:
<http://www.eppo.org/QUARANTINE/fungi/Verticillium_dahliae/VERTDA_map.htm>

Pictures:
Cited article <http://www.bspp.org.uk/ndr/july2006/2006-26.asp>
<http://www.apsnet.org/education/IntroPlantPath/Topics/fungicides/images/fig07.jpg>

Links:
<http://www.ipm.ucdavis.edu/PMG/r783100911.html>
<http://www.inra.fr/Internet/Produits/HYP3/pathogene/6verda2.htm>
<http://www.actahort.org/books/695/695_28.htm>
<http://www.minagric.gr/greek/data/files2251/PAPLOMA1.DOC.>
- Mod.JAD]