Técnica de amostragem para comparar o dano causado pela lagarta-da-espiga, Heliothis zea (Boddie), em cultivares de milho Sampling techniques to compare the damage by Heliothis zea (Boddie) in corn varieties

Neste trabalho, realizado no Instituto Agronômico, determinou-se o tamanho da amostra para estudos de danos causados pela lagarta-da-espiga, Heliothis zea (Boddie), avaliados pelo método de Widstrom. Foram utilizados dados de dois experimentos de campo, com um cultivar resistente (Asteca Prolífico VRPE VII), um suscetível (híbrido duplo IAC Hmd 7974), o 'Maya XVI' e o híbrido simples HS 7777, em 1978/79 e 1979/80. O critério para estimar o tamanho da amostra foi de que esse tamanho permitisse detectar uma diferença de 10 ou de 20% da média geral entre médias de danos, em cultivares de milho, e avaliar o dano médio por cultivar com erro-padrão de 10 ou de 20% da média. Para definir o processo de amostragem, utilizou-se o método de componentes de variância, estimados a partir de dois modelos matemáticos. O tamanho da amostra foi bastante variável entre cultivares, sendo maior no resistente. Entre os possíveis tamanhos mínimos de amostra para detectar uma diferença de 10% da média geral entre médias de danos de tratamentos, podem ser utilizados seis blocos com quatro linhas de 24 plantas; para uma diferença de 20% de média, cinco blocos com três linhas de seis plantas são suficientes. Para estimar a média de danos por cultivar, com erro-padrão de 10% de média, são necessários sete blocos com quatro linhas de 30 plantas, no cultivar Asteca, e cinco blocos com duas linhas de 24 plantas nos cultivares Hmd 7974, HS 7777 e Maya e, com erro-padrão de 20% de média, cinco blocos de três linhas com doze plantas, no 'Asteca', e cinco blocos com duas linhas de seis plantas nos demais cultivares.<br>A study was made to determine the sample size for research on corn resistance to corn ear worm Heliothis zea (Boddie). The damage was measured using the Widstrom centimeter scale. The criteria used to select the sample sizes were such that a difference between two treatments of ten percent or twenty percent of the overall mean should be detected by the statistical test, and that each treatment mean can be estimated with a standard error of 0.10 y or a standard error of 0.20 y. The data were obtained from two field experiments, carried out in Instituto Agronômico, Campinas, State of São Paulo, Brazil. The treatments were: cultivar Asteca Prolífico VRPE VII, which is resistant to Heliothis zea; Hmd 7974, a susceptible double hybrid; cultivars Maya XVI and HS 7777. A randomized complete block design with ten replicates was used, and each plot consisted of four rows with 50 plants per row. The variance components method was used to define the type of sampling. The most important variance component was due to the variability among units within rows. The following minimum sample sizes can be used to detect the difference between two means: 6 blocks with 4 rows of 24 plants for a difference of 0.10 y and 5 blocks with 3 rows of 6 plants for a difference of 0.20 y. For estimating the mean damage with 0.10 y as the half confidence interval on the mean of the population, the following minimum sample sizes can be used: for cultivar Asteca, 7 blocks with 4 rows of 30 plants per row; for the hybrids Hmd 7974, HS 7777 and cultivar Maya, 5 blocks with 2 rows of 24 plants per row. If a 0.20 y is specified, as the half confidence interval on the mean, it can be used 5 blocks with 3 rows of 12 plants for cultivar Asteca and 5 blocks with 2 rows of 6 plants for the other three cultivars

Reactions of the different breeding season corns as a function of injury of cotton bollworm (Helicoverpa armigera Hbn.).

The aim of present investigations was the increasing of knowledge of the cotton bollworm’s ( Helicoverpa armigera Hbn.) (CB) damages in the different breeding season corns. The damage examinations were made in a 29.2 hectares acreage between Igal and Kazsok villages (Somogy county) on the basis of the flight observation at the end of August 2008. We examined the measure of damages and yield losses based on the collected ears belonging to different breeding season corns (FAO 200–299, FAO 300–399, FAO 400–499, FAO 500–599). The relationship between the breeding season and the damages was examined by variance analysis (one-way anova). The collected samples were examined in analytic laboratory in order to calculate the quantitative alteration of the fundamental in-kernel air dry content values (raw protein, raw fat, starch).Our results proved the significant increasing of damage percentages (FAO 200–299: 8.66%; FAO 500–599: 15.33%), surface damages (cm 2 ) (P = 0.026) and the calculated weight loss of damaged ears (P=0.014) parallel with the increasing of the breeding season length. We confirmed the “forced maturing” in the case of the earlier hybrids in the consequence of the damage. We recorded a decreasing percentage (correlate to the draw matter) of the starch and the raw fat (average decreasing: starch: 1.72; raw fat: 0.26) as well as the increasing starch loss per one hectare, agreeing with the breeding season length increase (starch loss/one hectare: FAO 200–299: 1.54%; FAO 500–599: 2.72%). We observed the quantitative increasing of the raw protein as a function of CB’s damage too, which can be explained by a physiological response to the biotic stress