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<abstract language="eng">1) The object of the experiment presented in this publication was a detailed comparison between progenies of the varieties Virginia and Sumatra of the collection of the Instituto Agronômico de Campinas. We intended to decide whether these strains were sufficiently heterogeneous to permit further selections or whether they were already so uniform as to allow a reduction in their number within our collection. 2) A preliminary experiment in 1939/40 showed clearly that some of the 7 types introduced as Sumatra were less resistant than others, and the experiment was thus continued "with only four of them. 3) The lay-out of the final experiment was such as to permit both a complete analysis of soil heterogeneity and of differences between the genetically different lines. Without confounding there were only 3 complete replications, but after confounding we may dispose of 8 degrees of freedom for replications. This method of decomposing the total variation was used in the analysis of the vegetative characters. 4) The analysis of disease resistance could follow the same lines only the case of the infection of Sumatra by "spotted wilt" (2). There the main percentage of infected plants per plot was 60%, and the individual percentagens, without any further angular or other transformation, were used. In all other cases the number either of diseased or of not disease plants per plot was so small that these freguencies could only be compared with the corresponding Poisson distribuition. For this propose either a X² test was carried out or a comparison was only made between the error of a Poisson distribuition and the error directly determined from the data. 5) The blocks were reasonably homogeneous, soil heterogeneity causing only minor variation. 6) The plant characters such as height of plant, number of leaves and their dimensions showed a variation which was statistically significant, but without any practical importance as the data on pg. 280 show. The mean height was found to be 187,5 cm for Sumatra and 168,5 cm for Virginia the mean leaf number per plant - 25,7 and 22,8 - respectively and the mean index length of leaf - 37,3 and 44,4 - respectively. 7) All progenies within both varieties were equally little resistant against "spotted wilt", and soil heterogeneity caused a slight difference of resistance between the progenies of Virginia in Campinas. It is evident that the lines of Sumatra are more resistant than those of Virginia. 8) Infection by mosaic virus and the virus of "streak" (necrose branca-couve), was slight and the different progenies were equally resistant. As a whole, Virginia seems more resistant than Sumatra. 9) In short, there is a great homogeneity of the different lines of the varieties Sumatra and Virginia tested, and the prospect to their improvement by selection is negligible, both with regard to the vegetative characters studied or to disease resistance

Comportamento de variedades e progênies de fumo na resistência ao "vira-cabeça"