Gheorghe Popescu, Floarea Adam, Irina Oriol
In the period 2006/2007, in Arad region, in the experience on 8 „Pioneer” maize hybrids, we studied the interaction between  climatic factors, as independent variables, and the pathogens Helminthosporium turcicum, Fusarium roseum and Ustilago maydis, as pathosystem components whose aggression (F%) was used as dependent variable. In the statistical calculation of the variables mentioned, we used one of the best and most used statistical softwares, namely SPSS (Statistical Package for the Social Sciences). Regarding homogeneity, the high-degree factors were represented by „temperature”, „relative humidity” and „wind speed”, and the low-coefficient factors were „dew”, „nebulosity” and the dependent factor, namely the aggression of pathogens within the maize pathosystems -F%=33.84%; „moderation” characterizes independent variables’ influence on the dependent one. Regarding the intensity the dependent variable (F%) is influenced by the climatic factors (independent variables)  with, we observed: we may speak about strong influence when the climatic factors interfere, without „dew”; moderate influence – without „dew” and „nebulosity” and low influence – when only „wind speed” and „relative humidity”, of the 6 independent factors (temperature, RH, rainfall, dew, nebulosity, wind), interact. „Moderation”, too, characterizes the intensity of the correlation between influence factors and the resulting one. By excluding factors, step by step, from the „model”, the F%-favoring factors become evident, namely „temperature”, „rainfall”, „relative humidity”, „nebulosity”, „dew” and „wind”, less favored, although the statistical tests „t”, ”SIG”, ”Tolerance” and “VIF” (Variance Inflator Factor) produce negative values only for „rainfall”, „dew” and partially for „nebulosity”. ANOVA shows that the climatic factor with a major influence upon pathogen aggression is the „wind speed”, but it considers other factors that are not included in the software SPSS, too; the independent factor with negative influence on the dependent factor is the „nebulosity”. The testing of the „influence” factors excluded from data analysis has not led to significant results, because the independent variables excluded from models present a low degree homogeneity (they are characterized by „moderation” at the amplitude inferior level), a fact proved by the values of the tests ”t”, ”Sig”, „Tolerance” and „VIF”. ANOVA specifies that „wind speed”, a factor disseminating and amplifying pathogens’ activity, is the variable with the biggest influence on the factor F (pathogens); although this factor has had low values (homogenous), the aggression of the pathogens Helminthosporium and Fusarium has had high values (84.3%; 46.7%) – the explanation or the original conclusion, in national premiere, is that the new maize pest Diabrotica virgifera virgifera Le Conté expressed its role of „dissemination” and „amplification” of the pathogen agents mentioned. The attack produced by Ustilago was reduced and constant (13.62 – 14.0%), given this pest’s trophic attitude. The conclusions regarding the independent variables, dew, nebulosity and wind speed, are original (confirming or denying the conclusions available in the literature), and also the software SPSS initiated in the case of the other independent variables, and on the resulting factor, as well.
Helminthosporium; Ustilago; Fusarium; Pathogen; pathosystem; aggression; temperature; rainfall; wind; relative humidity; dew; nebulosity; statistics
Presentation: oral