Impact of osmotic and matric water stress on germination, growth, mycelial water potentials and endogenous accumulation of sugars and sugar alcohols on Fusarium graminearum

RAMIREZ M.L.; CHULZE SOFIA; MAGAN NARESH

MYCOLOGIA.

Mycological Society of America

Lugar: Stanford, USA.; Año: 2004 vol. 96 p. 470 - 478

0027-5514

Studies were conducted to determine the effect of osmotic (NaCl, glycerol) and matric (PEG 8000) water stress on temporal germination and growth of two F. graminearum strains over the water potential range of 20.7 to 214.0 MPa at 15 and 25 C. The effect on endogenous water potentials and accumulation of sugars and sugar alcohols also were measured. For both strains, germination occurred rapidly over the same range of osmotic or matric potential of 20.7 to 25.6 MPa after 4?6 h incubation. At lower osmotic and matric potentials (27.0 to 28.4 MPa), there was a lag of up to 24 h before germination. Optimum germ-tube extension occurred between 20.7 and 21.4 MPa for both strains but varied with the solute used. Growth was optimal at 21.4 MPa and 25 C in response to matric stress, with the minimum being about 28.0 and 211.2 MPa at 15 and 25 C, respectively. In contrast, F. graminearum grew fastest at 20.7 MPa and was more tolerant of solute stress modified with either glycerol or NaCl with a minimum of about 214.0 MPa at 15 and 25 C. A decrease in the osmotic/matric water potential of the media caused a large decrease in the mycelial water potential (Cc) as measured by thermocouple psychrometry. In general, the concentration of total sugar alcohols in mycelia increased as osmotic and matric potential were reduced to 21.2 MPa. However, this increase was more evident in mycelia from glycerol-amended media. The quality of the major sugar alcohol accumulated depended on the solute used to generate the water stress. The major compounds accumulated were glycerol and arabitol on osmotically modified media and arabitol on matrically modified media. In response to matric stress, the concentration of trehalose in colonies generally was higher in the case of osmotic stress. In each water stress treatment there was a good correlation between Cc and total sugar alcohol content.