Ap. Keinath et al., MORPHOLOGICAL, PATHOLOGICAL, AND GENETIC DIFFERENTIATION OF DIDYMELLA-BRYONIAE AND PHOMA SPP ISOLATED FROM CUCURBITS, Phytopathology, 85(3), 1995, pp. 364-369
Didymella bryoniae (anamorph Phoma cucurbitacearum), which causes gumm
y stem blight of cucurbits, occurs throughout the eastern United State
s. Other Phoma spp., such as P. exigua, also have been reported to cau
se symptoms of gummy stem blight. Twenty-seven isolates provisionally
identified as D. bryoniae or Phoma spp. were obtained from diseased wa
termelon, cantaloupe, cucumber, pumpkin, and squash grown in South Car
olina, New York, and Florida. D. bryoniae was clearly distinguished fr
om Phoma after 7 days of growth on quarter-strength potato-dextrose ag
ar at 24 C with a 12-h photoperiod. D. bryoniae produced white aerial
mycelium, olivaceous green substrate mycelium, and few pycnidia; Phoma
produced sparse aerial mycelium and numerous pycnidia, sometimes in c
oncentric zones. The percent monoseptate conidia for D. bryoniae isola
tes ranged from 0 to 18%, whereas no Phoma isolate produced any septat
e conidia. Seventeen of 19 D. bryoniae isolates were pathogenic on wat
ermelon cv. Charleston Gray and cantaloupe cv. Classic; all eight isol
ates of Phoma and two isolates of D, bryoniae were nonpathogenic. Geno
mic DNA was extracted from all 27 isolates described above plus two ad
ditional isolates of D. bryoniae from New York and one from Florida. D
NA was amplified using PCR primed with random oligonucleotide decamers
. RAPD amplification patterns clearly differentiated D. bryoniae from
Phoma. Each of five primers used produced two to four amplified fragme
nts that were unique either to all D. bryoniae or to all Phoma isolate
s. Thirteen additional fragments were present in all D. bryoniae isola
tes except two of the three isolates from New York.