Genética de Coffea. XX. Resultados preliminares do tratamento de sementes de café com raios-X

Abstract

Seeds of Coffea arabica L. were treated with X-rays in the betatron of the Department of Physics, University of São Paulo, in 1951 and 1952. Selfed seeds of the following types were treated : a) from several plants of the bourbon variety (C. arábica L. var. bourbon (B. Rodr.) Choussy )belonging to progenies that had been selfed for 4 or 5 generations ; b) two normal, diploid bourbon plants derived from haploid sporophytes by chromosome doubling ; c) one purpurascens plant (C. arabica L. var. purp urascens Cramer). A fourth set of seeds came from hybridizations between purpurascens and bourbon plants. Seeds to be treated were kept in the parchment (endocarp) and dried in the shade. Prior to treatment the parchment was removed, and the seeds were placed in petri dishes and exposed do X-rays in dosages varying from 4,200 to 150,000 r (table 1). Germination of the treated seeds was carried out on moistened filter paper in petri dishes. Out of 1,350 treated seeds 480 germinated, but only 31 seedling3 were secured. The axis of the embryos of seeds that received high X-rays' dosages did not reach more than 5 mm in length. When this size was attained the axis exhibited an abnormal thickening, accompanied by a greenish color and followed by death of the embryo. No seedlings was obtained from seeds that received more tham 14,000 r. The initial growth of the 31 seedlings from treated seeds was slower than that of seedlings from untreated controls. A few seedlings presented abnormal leaves and subnormal growth, probably as a result from the X-ray treatment. These seedlings as well as their progenies will be studied in the next years.