A SOIL-ON-AGAR METHOD TO EVALUATE ACID-SOIL RESISTANCE IN WHITE CLOVER

White clover (Trifolium repens L.) is adapted to the Appalachian regio n but is rarely found on strongly acid soils. To select for improved a cid-soil resistance we needed an effective and efficient soil-based pr ocedure. Our objective was to develop a simple, rapid, nondestructive technique that could be used to evaluate acid-soil resistance of clove r accessions. Our technique uses a thin layer of acid, Al-toxic soil o n top of solidified water agar. Germinated white clover seed, selected for uniform radical length of about 1 mm, are transplanted into the s oil. Root emergence from the soil into the agar is visually observed. We evaluated the technique using non-limed (pH 4.2, Al saturation 70%) and limed (pH 5.0, Al saturation 14%) Porters soil (coarse loamy, mix ed, mesic Umbric Dystrochrept) and four white clovers, two larger-leaf ed (ladino) clovers developed in the USA, and two smaller-leafed culti vars from New Zealand. Root emergence was observed daily for 10 d. Roo t emergence from the limed and non-limed soil began on day one and on day four, respectively. This delay in emergence indicates that the clo ver seedlings were responding to toxic factors in the acid soil that w ere alleviated by liming. The larger-leafed cultivars emerged more slo wly than the smaller-leafed cultivars in the non-limed soil but were s imilar to them in the limed soil. The soil-on-agar technique allows ea sy collection of root growth data, is rapid, nondestructive, and can b e used with large populations. The technique should be useful for char acterization of acid-soil resistance of white clover and other small-s eeded species. We suggest that seedlings whose roots emerge more quick ly from acid soil are more resistant than those whose roots emerge lat er and that the technique has promise for selecting resistant and susc eptible populations.