In vitro effect of substrate, temperature and photoperiod on Phakopsora pachyrhizi urediniospore germination and germ tube growth

Abstract

In vitro experiments were conducted to assess the effects of substrate, temperature and time of exposure to temperature and photoperiod on P. pachyrhizi uredospore germination and germ tube growth. The following substrates were tested: water-agar and soybean leaf extract-agar at different leaf concentrations (0.5, 1.0, 2.0 and 4.0 g of leaves and 15g agar/L water), temperatures (10, 15, 20, 25, 30, and 35oC) and times of exposure (1, 2, 3, 4, 5, 6, 7, and 8 hours) to temperature and 12 different photoperiods. The highest germination and germ tube length was found for the soybean leaf extract agar. Maximum P. pachyrhizi uredospore germination was obtained at 21.8 and 22.3°C, and maximum germ tube growth at 21.4 and 22.1°C. The maximum uredospore germination was found at 6.4 hours exposure, while the maximum germ tube length was obtained at 7.7 h exposure. Regarding photoperiod, the maximum spore germination and the maximum uredospore germ tube length were found in the dark. Neither spore germination nor uredospore germ tube growth was completely inhibited by the exposure to continuous light.

Asian Soybean Rust Severity Sowed in Different Seasons

“…The fungus spores are dry and are removed from uredia and transported by wind and deposited by sedimentation or impact by the wind on any surface. If they are deposited in soybean leaves and under more than 8h of continuous leaf wetness, low light intensity, they germinate, penetrate the leaves, initiating the infectious and sporulation process (Melching et al, 1989;Reis et al, 2004;Blum et al, 2015). On the other hand, these required conditions are not always met in the months following February sown, especially after April.…”

Analysis of combined strategies for the management of Asian soybean rust

“…The time of exposure to light directly affects the spore germination and the growth of the P. pachyrhizi germ tube. In a study by Blum et al (2015), it was found that spores submitted to the dark had a higher germination rate. Therefore, as the leaves of the upper part (and even of the middle part, depending on the cultivar and leaf area index) are more exposed to the sun, they tend to suffer less than the leaves of the lower part.…”

Hourly and daily changes on airborne urediniospores of Phakopsora pachyrhizi

“…The most favorable conditions to SAR epidemics reported are: (a) minimum leaf wetness (LW) of 6h per day; (b) optimum LW of 12-14h per day; (c) optimum temperature for spore germination of 18-26 o C; (d) optimum minimum temperature from 20 to 23 o C; (e) optimum maximum temperature inferior to 28 o C; (f) optimum minimum RH from 75 to 80%; (g) constant daily rain for 12-15 days (ALVES et al, 2007;BLUM et al, 2015;DEL PONTE et al, 2006;BONDE et al, 2007;ESKER, 2008;BONDE et al, 2013;DANELLI;REIS, 2016;DUFAULT et al, 2010b;ISARD et al, 2005;MARCHETTI et al, 1976;MELCHING et al, 1979;MELCHING et al, 1989;NASCIMENTO et al, 2012;YANEZ-LOPEZ et al, 2015). Under these conditions, from the urediniospores germination and hyphae penetration to new urediniospores formation, it takes 7-10 days (GARCÉS-FIALLOS, 2011).…”