Monitoring conidial density of Monilinia fructigena in the air in relation to brown rot development in integrated and organic apple orchards

Abstract

In a three-year Hungarian study, conidial density of Monilinia fructigena in the air determined from mid-May until harvest was related to brown rot disease progress in integrated and organic apple orchards. Conidia of M. fructigena were first trapped in late May in both orchards in all years. Number of conidial density greatly increased after the appearance of first infected fruit, from early July in the organic and from early August in the integrated orchard. Conidial number continuously increased until harvest in both orchards. Final brown rot incidence reached 4.3-6.6% and 19.8-24.5% in the integrated and organic orchards, respectively. Disease incidence showed a significant relationship with corresponding cumulative numbers of trapped conidia both in integrated and organic orchards, and was described by separate three-parameter Gompertz functions for the two orchards. Time series analyses, using autoregressive integrated moving average (ARIMA) models, revealed that the temporal patterns of the number of airborne conidia was similar in all years in both integrated and organic orchards. Conidia caught over a 24-h period showed distinct diurnal periodicity, with peak spore density occurring in the afternoon between 13.00 and 18.00. Percent viability of M. fructigena conidia ranged from 48.8 to 70.1% with lower viability in dry compared to wet days in both orchards and all years. Temperature and relative humidity correlated best with mean hourly conidial catches in both integrated and organic apple orchards in each year. Correlations between aerial spore density and wind speed were significant only in the organic orchard over the 3-year period. Mean hourly rainfall was negatively but poorly correlated with mean hourly conidial catches. Results were compared and discussed with previous observations.

Fungi Causing Storage Rot of Apple Fruit in Integrated Pest Management System and their Sensitivity to Fungicides

“…Apples from integrated orchards have a lower disease incidence in comparison to organic orchards in the case of brown rot (Holb, 2008). Similarly, apples from conventional orchards have been reported to have lower levels of storage rots (blue mold, brown mold and Bull's eye rot) in comparison with organic orchards (DeEll & Prange, 1993).…”

“…Climate conditions during growing season can also have a significant impact, for example, on spore dispersal and following brown rot incidence as it is proved in the conidial dispersal rates in the case of M. fructigena in organic and integrated apple orchards in Hungary (Holb, 2008).…”

Pest risk assessment ofMonilinia fructicolafor the EU territory and identification and evaluation of risk management options

“…It was estimated that one infected mummy per m 2 of orchard floor can produce more than 40 airborne Monilinia conidia per m 3 air (Villarino et al, 2010). The maximum hourly concentration of M. fructigena conidia detected in an apple orchard was in the range 200-250 conidia/m 3 (Bannon et al, 2009) and that of M. fructigena in the range of 120-395 conidia/m 3 air per day (Holb, 2008a;van Leeuwen, 2000, respectively): lower than concentrations measured in stone fruit orchards. A maximum concentration of 5000 conidia/m 3 was measured in a peach orchard with approximately 5% of the fruit infected by M. fructicola (Kable, 1965a).…”

“…At the end of each cycle, the fungus produces asexual conidia on all the affected plant surfaces, including blighted flowers/twigs, cankers, mummies, rotted fruit attached to the trees or fallen on the orchard floor, and thinned fruit (Bannon et al, 2009;Holb and Scherm, 2007;Hong et al, 1997;Van Leeuwen et al, 2002b;Villarino et al, 2010). These conidia are then dispersed, most of them remain viable (Holb, 2008a;Van Leeuwen et al, 2000;Xu et al, 2001) and can start a new infection cycle under favourable environmental conditions (Biggs and Northover, 1988b;Corbin, 1963;Corbin and Cruishank, 1963;Michailides and Morgan, 1997;Phillips, 1984). Therefore the density of the airborne conidia strictly depends on the density of the inoculum sources and, obviously, on the sporulation rate of the inoculum sources.…”

“…have been studied extensively (Corbin et al, 1968;Holb, 2008a;Kable, 1965a;Sanderson and Jeffers, 1992). Dehiscence of conidial chains in Monilinia is stimulated by a decrease in the ambient relative humidity (RH), but dehiscence and final capture of conidia may be separated in time (Byrde and Willetts, 1977).…”