Take-All Root Rot of St. Augustinegrass: First Report in Mississippi

Take-all root rot has been reported as a destructive disease of St. Augustinegrass home lawns in Florida and Alabama (1). In June 1998 and 1999, St. Augustinegrass home lawns in central Mississippi developed chlorotic, thinning patches ranging from 0.5 to 4.5 m in diameter. By August of each summer, plants within affected patches were necrotic and dead. Roots of affected St. Augustinegrass were necrotic and shorter than those of unaffected plants; nodes on stolons were necrotic, and lesions developed on internodes. Ectotrophic runner hyphae and dark brown, lobed hyphopodia were visible on roots and aboveground plant parts, respectively. Symptomatic tissues collected from St. Augustinegrass home lawns were plated onto potato dextrose agar (PDA); the incitant of take-all root rot, Gaeumannomyces graminis(Sacc.) Arx & Olivier var. graminis, was isolated. Verification of G. graminis var. graminis was based on colony morphology and taxonomic identification consistent with the description by Walker (2). G. graminis var. graminis isolated from symptomatic St. Augustinegrass was grown on sterile tall fescue seed and incorporated into sterile sand/peat moss mix. Asymptomatic St. Augustinegrass sprigs were washed, and roots were removed prior to planting in infested and noninfested soil. Plants were cultured in the greenhouse for 60 days. St. Augustinegrass planted into noninfested soil was asymptomatic while plants collected from G. graminis var. graminis-infested soil were symptomatic for take-all root rot. Crowns and roots of affected plants were necrotic; leaves were chlorotic and necrotic. Both runner hyphae and lobed hyphopodia were visible. G. graminis var. graminis was reisolated from symptomatic tissues and confirmed as the incitant of take-all root rot. This is the first report of take-all root rot of St. Augustinegrass in Mississippi. References: (1) M. Elliott. Plant Dis. 77:206, 1993. (2) J. Walker. Trans. Br. Mycol. Soc. 58:427, 1972.