Effect of a Water-Soluble Guar Root Extract on Spore Germination and Mycelial Growth of Various Fungi

Abstract

JOHNSON, D. A., and R. REINISCH. 1980. Effect of a water-soluble guar root extract on spore germination and mycelial growth of various fungi. Plant Disease 64:932-934. A water extract from the bark of guar roots inhibited germination of conidia and growth of mycelia of several plant pathogenic fungi. Germination of conidia and growth of mycelia of other test fungi were either stimulated or not affected by the extract. Fewer sclerotia were produced by Phymatotrichum omnivorum in soil with the extract than in soil without the extract. Additional key words: antifungal substance, Cyamopsis tetragonoloba, inhibition Field observations indicated that wheat (Triticum aestivum L.) double cropped with guar (Cyamopsis tetragonoloba (L.) Taub) is less severely infected by common root rot than is wheat double cropped with other crops or wheat not rotated with another crop (2). In addition, water extracts from the bark of guar roots inhibit germination of conidia of Bipolaris sorokiniana (Sacc. in Sorokin) Shoem. and decrease the severity of infection by B. sorokiniana in crowns and subcrown internodes of This investigation was supported in part by a research grant from Celanese Plastics and Specialties Co., Louisville, KY 40232. Approved for publication as Journal Article 15850 of the Texas Agricultural Experiment Station. Current address of senior author: Irrigated Agriculture Research and Extension Center, Prosser, WA 99350. 0191-2917/80/10093203/$03.00/0 01980 American Phytopathological Society wheat grown in environmental chambers (2). This study was undertaken to determine the effect of the extract from the bark of guar roots on the germination of conidia and growth of mycelia of several other fungi. MATERIALS AND METHODS The following fungi were used in this study: B. sorokiniana isolated from the subcrown internode of wheat; Cladosporium sp. Link ex Fr. isolated in the laboratory; Colletotrichum graminicola (Ces.) G. W. Wils isolated from sorghum, Sorghum bicolor (L.) Moench; a second culture of C. graminicola isolated from oats, Avena sativa L.; C. trifolii Bain isolated from alfalfa, Medicago sativa L.; Drechslera avenacea (Curt. ex Cke.) Shoem., isolated from oat; Drechslera turcica (Pass.) Subram & Jain isolated from sorghum; Fusarium moniliforme Sheldon and F. semitectum Berk & Rav. both isolated from sorghum; F. oxysporum Schlect. f. sp. vasinfectum (Atk.) Snyd. & Hans isolated from cotton, Gossypium hirsutum L.; Neocosmospora vasinfecta E. F. Sm. isolated from peanut, Arachis hypogaea L.; Phymatotrichum omnivorum (Shear) Dug. isolated from cotton; Puccinia recondita Rob. ex Desm. f. sp. tritici collected from wheat; Rhizoctonia solani Kuehn isolated from peanut; Sclerotium rolfsii Sacc. isolated from guar; Septoria tritici Rob. ex Desm. isolated from wheat; Ustilago tritici (Pers.) Rostr. collected from wheat; and Verticillium dahliae Kleb. isolated from cotton. Guar plants were collected from field plots, and the bark was stripped from the roots. Bark was air dried and then ground in a Wiley mill using a 20-mesh screen. Extracts of the bark were prepared from 35 g of ground bark stirred in 200 ml of methanol and then in 200 ml of acetone for 30 min. The mixture was passed through four layers of cheesecloth, and the methanol and acetone insoluble bark material was spread on a sheet of aluminum foil to air dry. This dried bark material was blended in 420 ml of water at low speed for 5 sec and then stirred for 1 hr. The mixture was drained and then squeezed through four layers of cheesecloth. The liquid portion was transferred to a beaker and placed in the refrigerator at 5 C for about 16 hr to allow sedimentation to occur. The upper solution was then pipetted from the beaker and flash evaporated to near dryness at 45 C; it was further dried and Table 1. Spore germination and germ tube growth of fungi exposed to two concentrations of guar root extracta Spore germination (%) Germ tube length (am)