3.7.73
USE OF POTASSIUM HYPOPHOSPHITE TO INHIBIT COLONY GROWTH OF CRYPTONECTRIA PARASITICA IN VITRO

A MORET, M NADAL, S LOPEZ and Y MATINEZ

Unit de Fitopatologia del Departament de Biologia Vegetal, FaG. de Biologia, Universitat de Barcelona, Av. Diagonal, 654, 080028 Barcelona, Spain

Background and objectives
This paper describes the chemical control of Cryphonectria parasitica (Murr.) Barr. (=Endothia parasitica [Murr.] PJ Anderson) in vitro using potassium hypophosphite. The fungus growth rate was determined in a PDA culture with different potassium hypophosphite concentrations (0 [control], 50, 100, 150, 200, 250, 300, 350 and 400 ppm). The resulting LD50 was found to be 206.6 ppm.

C. parasitica is the fungus responsible for chestnut blight. Virulent strains were responsible for severe damage to the European chestnut (Castanea sativa [Marsh.] Borkh.) at the turn of the century, but the fungus is also commonly found on several oak species, Quercus ilex Lin., Q. humilis Mill., Q. petraea(Maft.) Liebl. and Fagus spp. Chestnut blight is worldwide [1].

Material and methods
C. parasitica isolated from the branches and bark of European chestnut (Castanea sativa Mill.) was used to evaluate potassium hypophosphite inhibition of colony growth in vitro [2]. The fungus was cultivated in a PDA culture enriched with nutrient mineral solution [Ca(NO2), 1.6 g; KNO3, 0.4 g; KH2PO4, 0.4 g, Mg 504.7H20, 0.4 g; H20, 100 m]. Different concentrations of the potassium hypophospite (0 [control], 50, 100, 150, 200, 250, 300, 350 and 400 ppm) were added to media before autoclaving at 121C for 20 min. Ten plates were used for each concentration. 5 mm diameter plugs from a culture growing on PDA were placed in the center of Petri dishes containing 20 ml of each medium. Plates were placed in plastic bags and incubated in the dark at 24C. After 120 h two perpendicular measurements of the colony diameter were made and the average daily growth was calculated. The experiment was repeated and the LD50 was determined.

Results and conclusions
Using the average daily growth rate of the control (10.8 mm/day) and of the different concentrations assayed, we calculated the regression line as:
Y= -9.8988. 1 X + 7.1296 with a correlation coefficient of -0.93. By substituting Y of the equation of the regresion line by the half of the average daily growth of the control (5.4 mm) we obtain a LD50 of 205.6 ppm. These results demonstrate that the potassium hypophosphite considerably inhibits the growth in vitro of C. parasitica and, consequently, could be used to control it.

References
1. Roane MK, Griffin GH, Rush Elkins Jr., 1986. Chestnut Blight, other Endothia Diseases and the Genus Endothia. APS Monograph Series.
2. Moret A, Nadal M, Puigsaslloses N, 1991. Nutri-fitos, pp 93-95.