ABSTRACT
This study characterized 52 isolates of Monilinia fructicola from peach and nectarine orchards for their multi-resistance patterns to thiophanate-methyl (TF), tebuconazole (TEB), and azoxystrobin (AZO) using in vitro sensitivity assays and molecular analysis. The radial growth of M. fructicola isolates was measured on media amended with a single discriminatory dose of 1 µg/ml for TF and AZO and 0.3 µg/ml for TEB. Cyt b, CYP51, and ß-tubulin were tested for point mutations that confer resistance to quinone outside inhibitors (QoIs), demethylation inhibitors (DMIs), and methyl benzimidazole carbamates (MBCs), respectively. Eight phenotypes were identified including isolates with single, double, and triple in vitro resistance to QoI, MBC, and DMI fungicides. All resistant phenotypes to TF and TEB presented the H6Y mutation in ß-tubulin and the G641S mutation in CYP51. None of the point mutations typically linked to QoI resistance were present in the Monilinia isolates examined. Moreover, fitness of the M. fructicola phenotypes was examined in vitro and detached fruit assays. Phenotypes with single-resistance displayed equal fitness in in vitro and fruit assays compared to the wild-type. In contrast, the dual and triple-resistance phenotypes suffered fitness penalties based on osmotic sensitivity and aggressiveness on peach fruit. In this study, multiple resistance to MBC, DMI, and QoI fungicide groups was confirmed in M. fructicola. Results suggest that Monilinia populations with multiple resistance phenotypes are likely to be less competitive in the field than those with single resistance, thereby impeding their establishment over time and facilitating disease management.
ABSTRACT
This study aimed to characterize the quantitative and qualitative damage caused by Deois flexuosa (Walker) (Hemiptera: Cercopidae) adults in Axonopus catharinensis cv. SCS 315 Catarina and Cynodon dactylon (Tifton 85 and Jiggs cultivars) under different infestation densities and, consequently, the expression of tolerance-type resistance. For this purpose, potted plants were infested with different insect densities (0, 5, 10, 20, and 40 adults m-2). The impact of the infestation levels was assessed in the first growth cycle (10-day coexistence period) and in the regrowth (40 days after the first cut, without infestation) based on crop yield and chemical-bromatological composition as well as on photosynthetic pigments and hydrogen peroxide content. The principal component analysis relating infestation density and chemical-bromatological parameters showed a positive correlation between infestation density of D. flexuosa and the contents of neutral detergent fiber, acid detergent fiber, and the dry matter (DM). On the other hand, infestation density inversely correlated with the tillering rate, photosynthetic pigments (chlorophyll a and b, carotenoids), and iron content. In general, the impacts on DM production and chemical-bromatological composition were lower in A. catharinensis cv. SCS 315 Catarina when compared to the Cynodon species, possibly because A. catharinensis has higher tillering capacity and does not show a reduction in the photosynthetic pigments, which may act as compensating factors to D. flexuosa damage. Our results demonstrate that the A. catharinensis cultivar expresses tolerance-type resistance to D. flexuosa and constitutes an interesting option for pasturelands formation and diversification where this spittlebug species is an emerging pest.
Subject(s)
Hemiptera , Animals , Carotenoids , Chlorophyll A , Detergents , Hydrogen Peroxide , Iron , PoaceaeABSTRACT
Glomerella leaf spot (GLS) of apple is caused by three different Colletotrichum species complexes. This study evaluated the dispersal of Colletotrichum spores related to GLS temporal progress and defoliation. Spores were monitored by air and water runoff in different plant heights, and the temporal progress of GLS and defoliation were assessed. Spores of the pathogen were first cached in the lower part of the tree closer to the ground, confirming the importance of dead leaves on the ground as main source of primary inoculum. In plots with high primary inoculum, the disease increases exponentially during favorable weather conditions. The highest initial inoculum was found in the lower part of the tree, but the highest rate of the disease progress in the upper.
