Monilinia Vaccinii-Corymbosi(Sclerotiniaceae): Its Biology on Blueberry and Comparison with Related Species

Abstract

A six year study of Monilinia vaccinii-corymbosi in a 700 m2 site at Greenbelt, Maryland, revealed that this fungus attacks Vaccinium corymbosum and closely related species which, together, comprise the commercial blueberries of North America. Monilinia polycodii and M. taxonomic sp. 1 also grew at the site and, respectively, attacked V. stamineum and Gaylussacia baccata. Apothecia of M. vaccinii-corymbosi ejected viable ascospores for 2932 da; infection by ascospores caused leaf and shoot blight. Conidia were collected for 2547 da and they caused mummification of fruit. However the two inocula overlapped for several days when the bloom was 100%. In a growth chamber at 12 C, cups matured in 26 da beginning with the apical flattening of the stipe. Ascospores stored at 12 C, r.h. 50-65%, were viable for 23 da but no conidia germinated after 6 da. Occurrence of conidia on mummified fruits on plants of V. corymbosum and a technique to produce them in vitro are reported for the first time. Observations from inoculation of eight species of Vaccinium and one species of Gaylussacia with six species of Monilinia, and other data, revealed that the following are host specific: M. baccarum on V. myrtillus; M. ledi, anamorph on V. uliginosum, teleomorph on Ledum palustre; M. megalospora on V. uliginosum; M. oxycocci on V. macrocarpon and V. oxycoccos; M. polycodii on V. stamineum; M. urnula on V. vitis-idaea and M. taxonomic sp. 1 on G. baccata. The foregoing species, plus M. azaleae, and M. rhododendri are described, including their cultural characteristics. Useful taxonomic criteria include the extent of host specificity, the location of the ectostroma in relation to host epidermis and the parts in which it is lodged, the anatomical structure of the entostroma, and cultural characteristics. A dichotomous key is provided to delineate all Monilinia species on Monilinia vaccinii-corymbosi (Reade) Honey is an economically important fungus common on commercial blueberries in the United States and Canada. It is one of the 10 species of Monilinia Honey that attack plants of the ericaceous genera Vaccinium, Gaylussacia, Ledum, and Rhododendron. It causes symptoms rather similar to the effects of other Vaccinium-inhabiting species, and it is sometimes confused with M. urnula (Weinm.) Whet. (3, 4, 27). However, M. vacciniicorymbosi has a characteristically wide host range of related Vaccinium species and is otherwise distinct from all other Monilinia species. Monilinia has monilioid macroconidia (anamorph: Monilia), hollow-sphaeroid or (rarely) solid pseudosclerotia (a resting fungus mass enclosing substratum), and fructicolous apothecia (12, 25). The genus was segregated from Sclerotinia Fuckel, which now includes species with tuberoid, true sclerotia (a resting fungus mass) but lacking a conidial state.