Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 28, 1999
Publication Date: N/A
Interpretive Summary: White clover stolons are often rotted by fungal diseases during the hot, humid summers found in the southeastern US. Sometimes these diseases can completely kill the white clover stand. This study looked at a number of white clovers to determine their resistance to a fungal disease called Macrophomina phaseolina which can rapidly rot clover stolons and leaves. Both large and small-leaf plants were selected that showed resistance to this disease. A second test showed that, especially for large-leaf white clover plants, the selected plants were resistant to this disease. This disease may be one of the most important diseases affecting white clover stolons in the field since known field persistence of some white clovers related closely to their resistance or susceptibility to this disease. Additional tests in the field will determine if resistance to this fungal disease will improve the persistence of white clover stolons in pastures of the southeastern US.
Technical Abstract: Summer drought and hot temperatures, interspersed with short rain showers, create ideal conditions for fungal pathogenesis of white clover (Trifolium repens) stolons. Macrophomina phaseolina may be an important pathogen that limits survival of white clover stolons in the summer. This study evaluated 20 white clover cultivars, germplasms, and populations for resistance to M. phaseolina using a leaf tissue assay. Discs were cut from leaves excised from 50 plants of each entry and inoculated with an agar plug cut from a M. phaseolina colony. Leaf discs were scored according to the rate of necrosis induced by the pathogen. Differences in responses of entries to inoculation with M. phaseolina were observed in both runs of the experiment. Brown Loam Syn. 2 germplasm and North GA population had the least disease and the greatest number of plants selected as resistant to M. phaseolina. Large-leaf plants selected for resistance gave highly consistent responses when retested, with 35% of the plants having no leaf necrosis following inoculation with M. phaseolina. The leaf tissue assay was not as effective for selecting consistent resistant phenotypes among small-leaf white clover entries, as 37% of the plants selected as resistant were rated as susceptible upon retesting. Field testing of populations developed from this study will provide additional information on the importance of resistance to M. phaseolina for summer survival of white clover stolons.