No 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.

No abstract

Colletotrichum isolates obtained from apple leaves with symptoms of Glomerella leaf spot (GLS) can cause fruit rot and several small lesion spots– called here as Colletotrichum fruit spot (CFS). The objective of this work was to investigate the epidemiological relevance of Colletotrichum species, obtained from leaves with GLS, on causing diseases in apple fruit, and the influence of fruit size on symptom development. For this, five Colletotrichum species were inoculated in ‘Gala’ (Ø = 5.5 cm) and ‘Eva’ (Ø = 4.8 cm) fruit in the field (2016/17 season). Subsequently, C. chrysophilum and C. nymphaeae were inoculated in different fruit sizes (Ø = 2.4–6.3 cm) in the field (2017/18 and 2021/22 seasons) and in the laboratory. At harvest of the fruit inoculated in the field, only CFS symptoms were observed in both cultivars. In these evaluations for ‘Gala’, the CFS incidence reached 50% regardless of season, pathogen species and fruit size. For ‘Eva’, CSF were observed after inoculation with C. melonis in the 2016/17 season, and in smaller fruit inoculated with C. chrysophilum and C. nymphaeae in the 2021/22. In postharvest, rot symptoms occurred, and it was not associated with the small spots. It is concluded that Gala cultivar has a high susceptibility to CFS, caused by two Colletotrichum species of greatest epidemiological importance for GLS in Brazil, in all fruit sizes tested.