In Vitro, in Vivo and in Field Sensitivity of Venturia inaequalis to Anilinopyrimidine Fungicides with Different Types of Scab Management and Degree of Control

Abstract

The sensitivity of Venturia inaequalis to anilino-pyrimidine (AP) fungicides (pyrimethanil and cyprodinil) was studied on populations sampled from apple trees with different fungicide and APs histories: 1) apple trees in uncultivated areas never exposed to fungicides (wild types), 2) commercial orchards with many years of good scab control with APs (well-controlled); 3) populations in experimental Centre where an initial good activity decreased after several years of intensive use (poorly controlled). The in vitro sensitivity tests were performed on monoconidial isolates, while those in vivo with curative or preventive applications on populations inoculated on apple seedlings. In the field, the infection on apple trees was assessed as severity of attack on leaves. The results evidenced that the sensitivity in vitro to pyrimethanil and cyprodinil showed a progressive lower reduction from wild types to well controlled, ending with poorly controlled populations. In vivo tests the same moderate decrease of sensitivity and activity (with a wide range) was more evident with curative, respect preventive applications, as noticed also with an important DMI (difenoconazole). In field trials, the populations intensively treated with APs showed, after some years, a reduction of control, that was confirmed in the following years. These activity reductions were sensibly less strong respect those evidenced by strobilurins, both in field and in vitro tests. The particular characteristic of resistance to AP fungicides is discussed.

Unconventional Yeasts Are Tolerant to Common Antifungals, and Aureobasidium pullulans Has Low Baseline Sensitivity to Captan, Cyprodinil, and Difenoconazole

“…Resistance to CYP is rare in most orchards in the US and Europe, with the sensitivity thresholds for different pathogenic fungi in both regions set to between 0.03 and 5 mg/L [20,29,30,67,68]. Nevertheless, resistance has been noted and attributed to point mutations in the BcmetB gene and in nine different genes that encode mitochondrial proteins [69][70][71]. The wide range of MIC 50 values for CYP that were determined for A. pullulans (2.82-186 µg/mL) may be explained by the complex mode of action of CYP.…”

Research on Dithianon to Evaluate Suspects of Reduced Sensitivity of <i>Venturia inaequalis</i> with Different Methodologies in Italian Apple Areas

“…It is not clear why the activity of dithianon on apple seedlings was so low, considering that similar tests with seedlings on other fungicides as AP's [12] and DMI's [13] permit high correlation between this type of test and different sensitivities with reliable results, as shown by me. It was also advised by FRAC [14].…”

“…In some Italian apple areas the number of treatments with dithianon increased, over 10 or 15, caused by the occurrence of resistance to other fungicides, as QoI's [10], AP's [11] and DMI's [12].…”