Response to Leaf Inoculations with Macrophomina phaseolina in White Clover

Abstract

Summers in the southeastern USA produce a harsh environment for survival of white clover (Trifolium repens L.) stolons. Long periods of drought and hot temperatures are interspersed with rain showers that create ideal conditions for fungal pathogenesis. Previous studies indicated that Macrophomina phaseolina (Tassi) Goidanich may be an important pathogen that limits survival of white clover stolons in the summer. The objective of this study was to determine the range in response of 20 white clover cultivars, germplasms, and breeding and naturalized 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 the margin of a M. phaseolina colony. Leaf discs were scored according to the rate of necrosis induced by the pathogen. The experiment was conducted as a randomized complete block with four replicates and was repeated with 50 additional plants from each entry. Differences in responses of entries to inoculation with M. phaseolina were observed in each run 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 reliable 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. Resistance to M. phaseolina was observed in adapted white clover germplasm, and development of new cultivars with this resistance should improve white clover summer survival.