The brown rot fungi of fruit crops (Monilinia spp.), with special reference to Monilinia fructigena (Aderh. & Ruhl.) Honey

The brown rot fungi of fruit crops ( Monilinia spp.) cause blossom blight, twig blight, and fruit rot in rosaceous fruit crops in the temperate regions of the world. Three species are distinguished, of which M. fructicola and M. laxa are predominant in stone fruit culture, whereas M. fructigena is in pome fruits. This thesis deals partly with taxonomy and identification of the brown rot fungi, and with the epidemiology of M. fructigena in pome fruits.M. fructicola is considered as a quarantine organism for Europe, and adequate identification tools are essential to prevent the introduction of this species in Europe. The most important pathways that the pathogen can be carried on are imported fruits and nursery stock. An identification protocol was developed based on quantitative colony and germ tube characteristics to distinguish the three brown rot species. In a discriminant analysis, the combination of increase in colony diameter and length of the germ tube resulted in only two misclassifications out of 29 isolates tested. The ITS 1-5.8S-ITS 2 region of ribosomal DNA (rDNA) was sequenced for a wide range of isolates to support identification on the basis of morphology, and four distinct sequences were found. Japanese M. fructigena isolates differed from European ones by four transitions within the ITS 1 region and one transition in the ITS 2 region. Morphologically, significant differences were found in stroma formation and conidial dimensions between the Japanese and European group. A new Monilia anamorph was defined, Monilia polystroma Van Leeuwen, in which the Japanese M. fructigena isolates were included.In a two-years field study in an apple orchard, fruit loss caused by M. fructigena was quantified. In cv. James Grieve pre-harvest fruit loss ranged from 4.2 to 4.3 % in both years, in cv. Cox's Orange Pippin this was 4.4 % in 1997 and 2.7 % in 1998. The spatial distribution of diseased fruits among fruit trees, and that of trees with diseased fruits was analysed using Lloyd's index of patchiness (LIP) and spatial autocorrelation analysis respectively. Distinct clustering of diseased fruits among trees was detected in both cultivars in both years, whereas clustering of trees with diseased fruits did hardly occur. The concentration of airborne M. fructigena conidia in the orchard was monitored during two seasons, and related to ambient environmental conditions. Relative humidity, temperature, rainfall, wind speed and wind direction were monitored. The highest hourly concentration measured in 1997 was 233 conidia/m ³ and occurred during afternoon hours; in 1998 concentrations were lower than in 1997 throughout the season. Simple and multiple regression analysis was applied to relate weather variables to hourly spore catches. The factors relative humidity and temperature explained the variation in spore catches observed best.Mummification and (re)sporulation after infection of pome fruits by M. fructigena was studied in the field as well as under controlled environment conditions. Fruits of cv. Golden Delicious infected late in the season did not mummify, but sporulated profusely after overwintering. It was shown that early as well as late-in-the-season infected fruits contributed to the production of primary inoculum in the next season. Regeneration of conidia was much reduced in previously infected fruits after incubation under conditions of 20 and 25 °C and RH 65-85 % for 8 and 12 weeks