Resumo em Inglês:

The methods used in obtaining polyploid cassava (Manihot utilissima Pohl) by colchicine treatment were described in detail. Two solutions of colchicine were tried, one at 0.5% and other at 1.0%, both giving identical results in producing many altered plants. The chromosome number of the altered plants was determined and [a correlation between chromosome duplication and increase of the major diameter of stomata was found. Size of stomata in cassava serves to identify poliploids individuals if the plant produced by treatment is not a chimera, a very frequent event in producing polyploid cassava by colchicine. It was emphasized that the plants obtained by treatment were a type of chimera, with the aerial part polyploid and the subterranean base diploid. The development of polyploid individuals obtained from the polyploid aerial part of the treated was analyzed. A comparison between the tetraploid and the diploid control plants was made, the octoploid plant being too slow in development. There are many groups of polivalents in the first meiotic metaphase of the autopoly-ploid individuals obtained. By an analysis of the polen grains it was assumed that the diploid plant may be a structural hybrid. The production of the tetraploid plants was computed preliminarly, other detailed experiments involving spacing being necessary for estimating the commercial production,, since the diploid produces more branched plants than the tetraploid ones.

Resumo em Inglês:

The present paper deals with the virus disease of the tobacco plant recently described by Kramer & Silberschmidt (12) under the name "faixa das nervuras" (veinbanding). New host plants are added to the list of suscepts, as follows : Nicotiana repanda Willd., JV. angustifolia (*), N. Gossey Domin, N. Sanderae Hort. ex. W. Watson, N. glutinosa L., N. longiflora Cav., N. paniculata L., Lycopersicon esculentum Mill., L. pimpinellifolium Mill., and Cyphomandra betacea Sendt. Datura stramonium L., already studied by Kramer & Silberschmidt (12) and Nicotiana glauca Grah., Nicandra physaloides Gaertn., Solanum nodiflorum (**), S. nigrum L., Lactuca sativa L., Brassica oleracea L., Vigna sinensis Endl. var. Black., and Dolichos lablab L., var. purpurens were found not to be susceptible to the virus. (*) This species was received with this name from the Division of Tobacco and Plant Nutrition, U.S.D.A. (**) One plant of S. nodiflorum out of 22 which were inoculated gave symptoms of veinbanding. However as no backinoculation was made it can not be stated with certainty if it was truly affected by this virus. The symptomatology on tobacco described by the above mentioned authors agrees as a whole with which has been observed that is : clearing of the veins, chlorotic spotting and veinbanding. In addition it is stated that the white necrotic spotting found associated with the disease on certain tobacco varieties, v. g. Sumatra and Turkish must be attributed to the same virus. On potato plants of the varieties President and Green Mountain the virus causes local streak-like symptoms followed by chlorotic mottling of young leaves. Late symptoms take the form of leaf-drop streak. The virus of "faixa das nervuras" is easily transmissible through the sap giving practically 100% of success. The physical properties of the virus are : tolerance to dilution 1:10.000, thermal death point 54°C. and logevity in vitro 72 hours. No vector of the virus is known. The statement of Kramer & Silberschmidt (12) that the virus of "faixa das nervuras" belongs to the group of the potato virus Y is confirmed. A discussion is given about the position of the virus within the group. Our results do not permit to state that the virus is more related to the veinbanding virus as claimed by these authors. It is also pointed out that the differences found in the litterature between the Y and veinbanding viruses are slight, justifying in the maximum the separation of both, but as strains of the same virus.