Tratamento de mandioca pela colquicina: III análise comparativa entre clones diplóides e tetraplóides

Abstract

1) Tetraploid plants of cassava (Manihot utilissima Pohl) obtained by colchicine treatment are smaller than diploid plants and an analysis of their growing habits showed that tetraploid clones were not uniform and could be divided into two groups : group one : plants with stalks so thick as but shorter than the diploid plants: group two : plants wich stalks shorter as and thiner than the diploid ones (See tables 1 and 2). 2) Production of roots and stalks was studied in one experiment of randomized blocks and one vegetative cicle of the plants, (about 10 months); diploid clones are more productive and the tetraploid clones are very variable (Table 10). The Índice stalk/root weight is smaller in diploid clones, thus showing that production of roots in relation to stalks in the tetraploid plants is smaller than in diploid plants. Tetraploid plants are slower in growing habits during the beginning of the development (Figs. 18 and 20 to 24). 3) One experiment of randomized lines of 15 plants each and two vegetative cicles of the plants (about 20 months) confirms the results obtained in the experiment of one vegetative cicle regarding the production of roots and stalks. However, the indice stalk/root in plants with two vegetative cicles is the same (i = 0,30) for all clones (diploids and tetraploids) and is identical with the indice for diploid plants with one vegetative cicle, indicating that in plants with two vegetative cicles the production of roots in relation to stalks is the same both in diploid and tetraploid clones. 4) The production of roots and stalks was studied in one systematic experiment of 3 clones, in blocks of about 100 plants each: diploid clone n.° 8 and tetraploid clones n.° 2 and 6. The results obtained confirm the difference between tetraploid and diploid clones and also between the two tetraploid clones involved in the experiment (see table n.° 26 and figs. 25, 27 and 28.) The commercial value of tetraploid clones could be established only after other experiments (more tetraploid than diploid plants in the same area) since the production per plant of tetraploid clones is smaller than the diploid ones. The tetraploid clone n.° 6 has plants very small, of low production of roots and did not support field conditions. It is suggested that this clone should be good for horticultural conditions. 5) The starch contents is the same in all tetraploid and diploid clones studied (see table n. 28) and in two other clones of bitter cassava (n.°s 9 and 10) included for comparison in the analysis.