Summers in the southeastern USA produce a harsh environment for survival of
white clover (Trifolium repens L.) stolons. Long periods of drought and ho
t temperatures are interspersed with rain showers that create ideal conditi
ons for fungal pathogenesis. Previous studies indicated that Macrophomina p
haseolina (Tassi) Goidanich may be an important pathogen that limits surviv
al of white clover stolons in the summer. The objective of this study was t
o determine the range in response of 20 white clover cultivars, germplasms,
and breeding and naturalized populations for resistance to M. phaseolina u
sing 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 necrosi
s induced by the pathogen. The experiment was conducted as a randomized com
plete 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 n
umber of plants selected as resistant to M. phaseolina. Large-leaf plants s
elected for resistance gave highly consistent responses when retested, with
35% of the plants having no leaf necrosis following inoculation with M. ph
aseolina. The leaf tissue assay was not as reliable for selecting consisten
t resistant phenotypes among small-leaf white clover entries, as 37% of the
plants selected as resistant were rated as susceptible upon retesting. Res
istance to M. phaseolina was observed in adapted white clover germplasm, an
d development of new cultivars with this resistance should improve white cl
over summer survival.