The evaluation of leaf diseases of coconuts, Cocos nucifera L., known as large verrucose and small verrucose, caused by Sphaerodothis acrocomiae and Phyllachora torrendiella, respectively, come upon the problem of sampling method. Since there is not a consensual method for measuring coconut verrucose incidence, the present work was done with the objective of comparing two sampling methods of common use: method A: sampling six leaflets/plant in a single leaf; method B: sampling six leaflets/plant, from different leaves. The study was developed starting from three samples of 300 leaflets (ten plants x five leaves x six leaflets) collected in three coconut genotypes, in which the stromata number of large verrucose and of small verrucose were counted. Throughout these data the variance was calculated from the leaf in the plant and the leaflet in the leaf and plant, necessary for the estimated sample average in the two compared methods, as well in the other formulated alternatives. For the two diseases, in all the genotypes, the estimate of variance of the sample mean calculated by the A method was higher than the one calculated by the B method, showing that the last method is more appropriate than the first one. Other sample sizes were also studied and compared by the B method, resulting that sample of two or three leaflets collected in six leaves per plant decreased sample variance on respectively 20% or 30%, probably being of more accurate applicability.
Cocos nucifera; plant diseases; fungi; leaves; analytical methods
