Disease Note.

First Report of Monosporascus Root Rot/Vine Decline of Watermelon in Tunisia. R. D. Martyn, Department of Plant Pathology & Microbiology, Texas A&M University, College Station 77843. B. R. Lovic, D. A. Maddox, A. Germash, and M. E. Miller. First and second authors: Department of Plant Pathology & Microbiology, Texas A&M University, College Station 77843; fifth author: Department of Plant Pathology & Microbiology, Texas A&M University, Weslaco 78596; third author: Seed Testing of America, Longmont, CO 80501; and fourth author: INRAT, Tunis, Tunisia. Plant Dis. 78:1220. Accepted for publication 19 September 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1220B.

During the summer of 1994, watermelon cv. Giza (Citrullus lanatus (Thunb.) Matsum. & Nakai) in commercial fields near the coastal city of Gabes in southern Tunisia exhibited severe symptoms of vine decline, including yellowing and collapse of the foliage several weeks before harvest, exposing the fruit to intense solar radiation. Root systems of affected plants were necrotic, with numerous discrete lesions and lacked most secondary and tertiary roots. Lateral roots bore numerous black, erumpent, fruiting structures, suspected to be perithecia of the fungus Monosporascus. Root samples sent to the senior author's laboratory for identification were received in July 1994, approximately 6 wk after collection. The root tissue was generally deteriorated, but perithecia were readily visible. Based on visual inspection of perithecia and ascospores, the fungus was tentatively identified as Monosporascus cannonbalhis Pollack & Uecker. Attempts to isolate Monosporascus from the roots were unsuccessful due to the extended length of time the samples were in transit and the fact that ascospores do not germinate under laboratory conditions. DNA extracted from small (2-5 mm) pieces of root tissue and individual perithecia plus DNA from both mycelia and ascospores of a Texas isolate of M. cannonballus was amplified for 45 cycles via PCR in a Perkin Elmer Cetus 480 thermal cycler using Monosporascus-specific primer pair A+D derived from the internal transcribed spacer regions of the ribosomal DNA repeat unit (1). PCR products were resolved by electrophoresis in 1.2% agarose gels containing ethidium bromide. A single 430-bp fragment indistinguishable from that of known isolates of M. cannonballus was observed in all samples except the negative control. To further confirm the identity of the amplification product, the DNA was transferred onto a nylon membrane by Southern blotting and hybridized with a digoxigenin-labeled probe consisting of a portion of the ITS2 region. This probe hybridized to the 430-bp fragment amplified from both the perithecium and root tissue from Tunisia, which confirmed the identification as M. cannonballus. M. cannonballus is a recently described fungus that causes a severe root rot/vine decline of watermelon and muskmelon in Texas and Arizona (USA), Spain, and Japan (2). This is the first confirmed report of this pathogen in Africa; however, a disease of unknown etiology with identical symptoms on watermelon was described from Tunisia by the senior author in 1983.