Sampling in the evaluation of the coconut verrucoses

The evaluation of leaf diseases of coconuts, Cocos nucifera L., known as la rge verrucose and small verrucose, caused by Sphaerodothis acrocomiae and P hyllachora torrendiella, respectively, come upon the problem of sampling me thod. Since there is not a consensual method for measuring coconut verrucos e 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 pl ants x five leaves x six leaflets) collected in three coconut genotypes, in which the stromata number of large verrucose and of small verrucose were c ounted. Throughout these data the variance was calculated from the leaf in the plant and the leaflet in the leaf and plant, necessary for the estimate d sample average in the two compared methods, as well in the other formulat ed alternatives. For the two diseases, in all the genotypes, the estimate o f variance of the sample mean calculated by the A method was higher than th e one calculated by the B method, showing that the last method is more; app ropriate than the first one. Other sample sizes were also studied and compa red by the B method, resulting that sample of two or three leaflets collect ed in six leaves per plant decreased sample variance on respectively 20% or 30%, probably being of more accurate applicability.