Peach and nectarine susceptibility to brown rot and protocol optimization to evaluate Monilinia fructicola sporulation

Abstract

The fungus Monilinia fructicola, which causes brown rot in fruits, is one of the main peach pathogens. The emergence of fungicide-resistant fungus isolates, as well as the attempt to reduce sprays, favors adoption of other control strategies. Among them, one of the most important is genetic resistance. This study was carried out aiming to evaluate the susceptibility of 16 peach and 4 nectarine genotypes to brown rot, as well as to evaluate how well the sporulation area and diameter correlate with number of spores in the lesions. Both wounded and non-wounded fruits were inoculated with 10 μL of M. fructicola suspension. Wounded fruits from all genotypes (nectarines and peaches) showed susceptibility to M. fructicola, from 92 to 100% of incidence. The disease incidence was between 18 and 100% when non-wounded fruits were inoculated. High variability was detected for the fungus sporulation, in both wounded and non-wounded fruits, with ranges between 16 to 96% and 0 to 94%, respectively. The fungus sporulation was variable among the genotypes (between 0.1 to 96.0 conidia per mm2) and it is positively correlated with the diameter and area of sporulation. The genotypes Conserva 947, Conserva 1662, Conserva 672, Conserva 1600, and 'Bolinha', are the ones with less susceptible to brown rot.

Breeding Peaches for Brown Rot Resistance in Embrapa

“…The procedure adopted for inoculations was the same described by Dini et al [24]. Briefly, the fungus isolate was obtained from four peach orchards in Embrapa Clima Temperado.…”

“…For the wounded inoculations (penetration of 1 mm into the fruits) a 100 µL syringe coupled to a repeating dispenser 50× (Hamilton ® ) was used. In both treatments (W and NW) 10 µL suspension of M. fructicola (2.5 × 10 4 conidia mL −1 ) and Tween-80 ® (0.1 g L −1 ) was used, followed by incubation at 23 ± 1 • C and 12 h photoperiod for three days [16,18,19,[24][25][26][27].…”

“…Incidence and severity 72 h after inoculation (HAI) were evaluated according to Dini et al [24]. Brown rot incidence (BRI) and sporulation presence (SPP) were calculated as the percentage of fruits that presented symptoms and sporulation of M. fructicola, respectively; lesion diameter (LD) and sporulation diameter (SPD) were evaluated through two perpendicular measurements per fruit in the equatorial region; lesion area (LA) and lesion sporulation (SPA) were calculated and expressed as the percentage of fruit that was affected by the lesion and sporulation, respectively.…”