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<abstract language="eng">1. Since our experiments on tobacco during the past years were greatly prejudiced by the extreme effect of the infection by the virus of the "vira-cabeça" causing the death of the great majority of the plants attacked, it was considered necessary to carry out an extensive experiment in order to determine whether there are differences: between localities, between varieties, between times of planting. Thus the experiment was carried out during 3 years in four Experiment Stations in the State of São Paulo: (Campinas, Piracicaba, Tietê e Limeira). In the first year 10 varieties were included and later on their number was reduced to 6. It was planed to sow and plant at regular time intervals and simultaneously in all Exp. Sta's, but this turned out to be impossible. Table 1 gives the dates of the transplanting actually carried out. In each year and Exp. Sta., the plots containing one variety each were distributed within blocks at random and there were 3 complete replications of block. Standard plots contained 30 plants in 29,92 m² in 1937/38 and 48 plants in 39,46 m² during the other two years. " 2. The disease "vira-cabeça" seems to be identical with "spotted wilt" and "krom-neck" (2). 3. Very pronounced differences of the mean percentages of infection were established in different years, in the four Exp. Sta's and at different times. But these differences are without any evident order, and the time intervals were so irregular, they could not be put in contrast with meteorogical events. Consequently this part of the experiment has to be continued, and more detailed results are already available, but not yet fully analysed. 4. Differences between varieties are also quite evident and their significance was established both by the analysis of variance and the subsequent t-test as well as by the order test (1). The variety Sumatra V 38 was definitely the most resistant. Leaving aside the results of Campinas where infection is always abnormaly high, the percentage of infected plants per plot varied between 0,4 and 8,8% in 1939/40 and between 11,0 and 2,27 in 1938/39. Unfortunately the variety Sumatra is of no economical importance at the moment in São Paulo. The variety Amarelinho V 33, which according to its characters and the bright color of its leaves is indicated as one of the more important types for cigarette manufacture, belongs to the middle group with only slight resistance. 5. The practical results of theses experiments may be briefly summarized as follows. a). It seems indicated to transfer our work to regions were the ocurrence of "spotted wilt" is, at least so far, negligible. b) The selection of the most favorable time of planting has to be ascertained in new experiments, which are already well under way. That the meteorogical conditions have a very great importance has been established beyond doubt. c) There are no really resistant varieties. Experiments to transfer the relative resistance form Sumatra to bright tobaccos such as Amarelinho are under way. d) It seems doubtfull whether the inclusion of more varieties will lead to the detection of a more resistant variety or strain. e) But it seems especially indicated to estend the experiment in the future with the intention of finding an eficient way of combating the insects which transfer the disease

Ensaio de épocas de transplante para o fumo