6.10
MINIMAL NUMBER OF REPLICATIONS FOR EVALUATION OF MYCELIAL GROWTH AND SPORE DIMENSIONS

MDM PORTO, LMC DUTRA and OA LUCCA FILHO

Faculdade de Agronomia, UFRGS, Caixa Postal 776, CEP 90012-970 Porto Alegre, RS, Brazil

Background and objectives
Spore dimensions are often referred to as an important characteristic of fungal species. Variations in mycelial growth are also mentioned, but not so frequently. The authors, however, rarely mention how many spores were measured or how many colonies were evaluated. This research was carried out in order to define the minimum number of replications required for characterizing these two variables within some limits of confidence.

Materials and methods
Mycelial growth was determined only with Phomopsis phaseoli f.sp. meridionalis. The fungus was grown on potato dextrose agar medium and incubated at 25 and 30C. Each day the contours of the colonies were drawn on transparent film and submitted to a leaf area integrator. Spores of 13 fungal species, including the one referred to above, were measured with the aid of a micrometer. The data were submitted to statistical analysis to define the number of replications required for every difference (5, 10, 15 and 20%) above the average to be significant (t-test) at 1 and 5% probability levels. A similar method has already been used [1].

Results and discussion
The proposed technique allows the researcher to define the number of replications based on the precision required. Mathematical equations can be developed for each case. It is possible to work with a low number of colonies and spores if the experimental error is kept under control. For instance, in the measurement of spores, the length of time has to be the same for all the preparations.

References
1. Dutra LMC, Porto MDM, Camacho D, Storck L. 1996. Fitopatologia Brasileira 21 (Supl.), 356.