Fungicide sensitivity and monocyclic parameters related to the Phakopsora pachyrhizi–soybean pathosystem from organic and conventional soybean production systems

Abstract

The failure of chemical control of soybean rust has been related to the selection of less sensitive isolates, and the infection capacity of such isolates could have implications for the management of the disease. The aims of the present study were to compare the sensitivity to tebuconazole and azoxystrobin and the monocycle of soybean rust using isolates of Phakopsora pachyrhizi from two soybean fields with different production systems (organic and conventional) in 2012/13 and 2013/14 seasons, and to monitor mutations in the CYP51 gene. To assess the sensitivity to tebuconazole and azoxystrobin, detached leaf tests and in vitro germination, respectively, were used. To evaluate the monocycle, detached leaves were inoculated with a urediniospore suspension and evaluated daily by counting the number of uredia. The occurrence of the mutations in CYP51 was investigated by a pyrosequencing assay. In both 2012/13 and 2013/14 seasons, the EC 50 to tebuconazole was lower for the population from the organic system (0.41 and 0.10 lg mL À1 , respectively) compared to the conventional system (1.60 and 4.44 lg mL À1 , respectively), while the EC 50 to azoxystrobin was similar for both populations. The lower sensitivity to tebuconazole and azoxystrobin was associated with F120L + Y131H mutations in CYP51, and the F129L mutation in CYTB, respectively. The monomolecular model fitted to monocycle data and parameters related to the maximum asymptote and the AUDPC were superior for organic than the conventional system.

Lack of an Intron in Cytochrome b and Overexpression of Sterol 14α-Demethylase Indicate a Potential Risk for QoI and DMI Resistance Development in Neophysopella spp. on Grapes

“…The F129L mutation was detected in P. pachyrhizi in the 2012 to 2013 season after many years of QoI use in soybean in Brazil (Klosowski et al 2016). Later on, azoxystrobin sensitivity assays revealed that F129L mutant isolates displayed higher EC 50 values, ranging from 2.10 to >10 µg/ml, compared with EC 50 values of wildtype isolates that ranged from 0.14 to 1.46 µg/ml (Klosowski et al 2018). Resistance of P. horiana to azoxystrobin has been reported in the United Kingdom (Cook 2001); however, no variation was found between CYTB sequences from sensitive and resistant isolates, suggesting that other resistance mechanisms may be involved (Grasso et al 2006b).…”

Covering Soybean Leaves With Cellulose Nanofiber Changes Leaf Surface Hydrophobicity and Confers Resistance Against Phakopsora pachyrhizi

“…Synthetic fungicides are the primary ASR disease control method. However, fungicide use can cause many problems such as environmental impacts (Maltby et al, 2009), increased production costs (Godoy et al, 2015), and the emergence of fungicide-resistant pathogens (Langenbach et al, 2016;Klosowski et al, 2018). Another major and effective control method is breeding or engineering of ASR resistant soybean cultivars.…”

Profitability of fungicide applications for managing soybean rust in scenarios of variable efficacy and costs: A stochastic simulation

“…pachyrhizi strains to tebuconazole in Brazil (Brent & Hollomon, 1995; Schmitz et al, 2013). Similarly, mutations associated with QoIs and succinate dehydrogenase inhibitor (SDHI) fungicides, the most recent group introduced to compose dual or triple mixtures, have recently been found (Klosowski et al, 2016, 2018; Simões et al, 2018).…”