SAMPLE SIZE FOR ASSESS THE LEAF BLAST SEVERITY IN EXPERIMENTS WITH IRRIGATED RICE

Bruno Giacomini Sari,Ana Lúcia De Paula Ribeiro,Ivan Francisco Dressler Da Costa,Alessandro Dal'Col Lúcio

doi:10.1590/1983-21252016v29n406rc

Bruno Giacomini Sari, Ana Lúcia De Paula Ribeiro + Show 2 more

Open Access

https://doi.org/10.1590/1983-21252016v29n406rc

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Abstract

ABSTRACT The aim of this study was to determine the sample size needed to assess the severity of leaf blast in rice in experiments with different fungicide treatments. The severity and the area under the disease progress curve data of three chemical disease control treatments carried out in Rio Grande do Sul, were used in the study. Analysis of variance was performed to verify whether the severity of the disease differed between treatments. The spread of disease was was also found to be different between treatments and assessments, using the variance/mean ratio and Morisita index. The spatial distribution of the disease among the treatments and during the evaluations is important for the choice of the equation used to calculate the sample size. The spatial distribution of the disease was not the same across the experiments, and it varied between treatments and evaluations. Thus, we decided to use a formula that was not associated with distributions to indicate the spatial distribution (negative binomial or Poisson) of the disease in the field. The sample size to estimate the average of rice leaf blast severity varied between treatments and evaluations. The area under the disease progress curve is necessary to be determined to reduce the number of samples needed. Thus, it is recommended to assess 293 sheets to estimate severity, and 63 to estimate AUDPC at 20% error.

Highlights

The leaf blast caused by the fungus Pyricularia grisea (Cooke) Sacc. (=Pyricularia oryzae Cavara) is a disease commonly found in irrigated rice
Owing to the high potential for damage caused by leaf blast on rice, research on fungicide efficiency is critical for proper disease management, as well as to find an alternative way to chemical control, which is one of the main methods to control rice leaf disease (CELMER et al, 2007; SANTOS et al, 2008)
Sampling within the plot generates a new variance within the plot, and this should be minimized by an appropriate sample size (CARGNELUTTI FILHO et al, 2009)

Summary

Introduction

The leaf blast caused by the fungus Pyricularia grisea (Cooke) Sacc. (=Pyricularia oryzae Cavara) is a disease commonly found in irrigated rice. The leaf blast caused by the fungus Pyricularia grisea (Cooke) Sacc. (=Pyricularia oryzae Cavara) is a disease commonly found in irrigated rice. The disease occurs in all rice-producing areas and results in yield losses that can reach 100% (FILIPPI et al, 2007). The quality of the results obtained depends on experimental precision. The experimental error corresponding to the variation between repetitions of the same treatment must be minimized so that the effect of the treatments is reliably estimated (CATAPATTI et al, 2008). Experimental precision can be improved by the proper sizing of the number of repetitions and choice of experimental design (STORCK et al, 2006; CATAPATTI et al, 2008). Many variables must be obtained by sampling experimental plots (KRAUSE et al, 2013), since the entire population cannot be sampled due to the excessive demand for labor, time, and financial resources. Sampling within the plot generates a new variance within the plot, and this should be minimized by an appropriate sample size (CARGNELUTTI FILHO et al, 2009)

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