The soybean rust can be caused by two fungus species of the genus Phakopsora: P. meibomiae and P. pachyrhizi. The safest method to separate the both species is based on morphologic characteristics of the teliospores. This study was carried out to determine the effect of temperature in telia formation and to observe both telia and teliospore morphometry present in leaflets of soybean plants. Seeds from two soybean cultivars, 'Uirapuru and Pintado', were sowed in pots with 3 kg of substrate. Thirty days after sowing, plants on the growth stage V3 were inoculated with urediniospores of P. pachyrhizi and kept in glasshouse for disease development. Upon the appearance of disease symptoms (seven days after inoculation), plants were moved to growth chambers at the temperatures of 10, 15 and 20ºC. At fifteen days later, leaflets were observed for the presence of telia and teliopores. Typical pustules containing telia were observed under stereomicroscope on leaflets from plants of the cultivar 'Uirapuru' and 'Pintado' growing at 15ºC at the 25th and 30th days, respectively. The presence of telia was confirmed by fine sections from fresh material and observations of the sections in light microscope and scanning electron microscope. Two types of telia were observed: one round-elliptical with width of 35.25 µm and length of 77 µm, on cultivar 'Uirapuru' and other type measuring 41.33 µm width and 127.33 µm length on cultivar 'Pintado'. The shape of the teliospore also varied between the cultivars. Oblong spores were more frequent on the cultivar 'Pintado' and subglobose on cultivar 'Uirapuru'. The dimensions of the teliosporos were of 6.87 µm of width for 14.91 µm of length and distal wall of the apical cell of 1.90 µm on cultivar 'Pintado' and 7.02 µm of width for 10.02 µm and distal wall of the apical cell of 1.43mum on cultivar 'Uirapuru'.
soybean rust; morphometry
