Inducing autotetraploids in cassava using oryzalin and colchicine and their in vitro morphophysiological effects.

Polyploid induction has been used for plant breeding to produce bigger and more robust plants than diploid types. The present study aimed to develop a methodology for in vitro induction of polyploidy in cassava. Apical and lateral microcuttings from the BRS Formosa variety were treated with six oryzalin concentrations for 24 and 48 h. The same methodology was used for colchicine with different concentrations. After 45 days of cultivation and an additional 45 days of subculture, the viability of the explants was assessed and plant acclimatization was performed. Ploidy was determined using flow cytometry. Oryzalin dose and exposure negatively affected cassava explant growth and development compared to untreated explants. Furthermore, apical and lateral explants responded differently to the treatments, showing a diversity in antimitotic sensitivity and effect that is tissue-type specific. In contrast, the doses of 1.25 to 6.25 mM colchicine resulted in high mortality of cassava explants. Therefore, the type of antimitotic affects the morphophysiological behavior of cassava plants in vitro, although apical explants have higher viability and regenerative capacity compared to lateral explants. In addition, the lateral explants have lower mixoploid rates compared to apical explants. Of the 310 plants generated by oryzalin treatments, 277 were diploid, 31 were mixoploid, and 2 were tetraploid. Exposure to oryzalin led to low rate of tetraploids and colchicine caused phytotoxic reactions and death of the explants. The tetraploids were multiplied in vitro to evaluate their yield in the field as well as their behavior against abiotic and biotic stress.

[Physical activity in a probabilistic sample in the city of Rio de Janeiro]. / Atividade física em uma amostra probabilística da população do Município do Rio de Janeiro.

This study evaluated physical activity in a probabilistic sample of 4,331 individuals 12 years of age and older residing in the city of Rio de Janeiro, who participated in a household survey in 1996. Occupation and leisure activity were grouped according to categories of energy expenditure. The study also evaluated number of hours watching TV, using the computer, or playing video-games. Only 3.6% of males and 0.3% of females reported heavy occupational work. A full 59.8% of males and 77.8% of females reported never performing recreational physical activity, and there was an increase in this prevalence with age, especially for men. Women's leisure activities involved less energy expenditure and had a lower median duration than those of men. Mean daily TV/video/computer time was greater for women than for men. The greater the level of schooling, the higher the frequency of physical activity for both sexes. Analyzed jointly, these data show the low energy expenditure through physical activity by the population of the city of Rio de Janeiro. Women, the middle-aged, the elderly, and low-income individuals were at greatest risk of not performing recreational physical activity.