Identificação molecular e indução de télia no patossistema Phakopsora pachyrhizi-soja

Abstract

The soybean [Glycine max (L.) Merrill] crops currently cultivated present significant differences its ancestrals, originated in Asian east region. With the extension of cultivating areas of that leguminous the soybean rust became a serious problem to the farmers. That disease is caused by two species: Phakopsora pachyrhizi, the "Asian" and to P. meiborniae, the "American". P. pachyrhizi is known by reducing the production drastically and its fast expansion has been causing severe losses in the field, meaning that such pathogen is one of the most destructive to soybean with impact in the soybean production in Brazil and in the world. Due to the lack of information on the species causing soybean rust in Brazil and Minas Gerais State, this work had as objective to characterize soybean rust uredospores, in leaves collected in producing areas in the State of Minas Gerais by molecular methods also to study the induction of the telia by this pathogen on different temperatures. The molecular characterization done through PCR with the specific primers Ppml/Ppa2 for P. pachyrhizi and Ppml/Pme2 for P. meibomiae, showed that all the 86 samples collected in the State of Minas Gerais were of the species P. pachyrhizi. For the induction of the telia 3 differents growth chambers with temperatures of 10°C, 15°C and 20°C and two cultivate of soybean, Pintado and Uirapuru were used. The plants were inoculated 30 days after sown and after 7 days of the inoculation they were placed in the growth chamber with the mentioned temperatures. The evaluations had beginning after 15 days transference for each camera, the observations were made in microscope stereoscope every five days, and for any lesion suspects it was made cuts in table microtome, and analyzed in light microscope. At 25 days after started the readings was observed telias in leaves from growth chamber with 15°C in the cultivar Uirapuru, and to the 30 days in cultivar Pintado, respectively. It was confirmed with fine cuts of the fresh material and observation to the light microscope with increase of 400x and scanning electron microscope two types of telia were observed, one round-elliptical with width of 77 gm and length of 35.25 gm and apical layer of 1.42 gm, on cultivar Uirapuru, the other type measuring 127.33 gm of width and 41.33 itm length with apical layer of 1.9 gm of the cultivar Pintado. The shape of the teliospore also varied among the cultivars, in the cultivar Pintado slave shape spores were more frequent measuring 6.97 gm of width and 14.91 prn of length. In the cultivar Uirapuru teliospores were rounder with size 7.02 gm x 10.02 grn of length.