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WISCONSIN CRANBERRY FIELD. P. G. Sanderson and S. N. Jeffers. 232
Dept. of Plant Pathology, Univ. of Wisconsin, Madison 53706.
VIRULENCE OF SINGLE AECIOSPORE ISOLATES OF CRONARTIUN QUERCUUN
A Burkard 7-day recording volumetric spore trap was used to F. SP. FUSIFORME. E.G. Kuhlman and F.R. Natthews, USDA,
determine when spores of Monilinia oxycocci, the causal agent Forest Service, SEFES, Athens, GA, 30602.
of cranberry cottonball, were present in a commercial cranberry
field. In 1987 and 1988, ascospores were first detected on 5 Single gall isolate LHNC-2 produced galls on twice as many
May, ca. one week before bud break, and continued to be trapped seedlings of rust resistant loblolly pine family 10-5 as
until one week before bloom. They occurred for 31 consecutive did standard composite isolate 1-73. Thirty-two single
days in 1987 and 28 consecutive days in 1988. Conidia were aeciospore isolates from LHNC-2 were used to produce basidiospore
first detected ca. 10 days before bloom in 1986, at the start inoculum for inoculating seedlings of family 10-5. Six
of bloom in 1987, and at 507 bloom in 1988. Conidia were weeks after inoculation symptoms were unusually frequent.
present for 34, 30, and 26 consecutive days beginning 7, 6, and Three months after inoculation with the single aeciospore
17 June in 1986, 1987, and 1988, respectively. The two spore isolates, the percentage of seedlings with galls varied
types never occurred concurrently. Both ascospores and conidia from 33-85. In the same experiment isolate LHNC-2 and 1-73
exhibited a diurnal periodicity. Ascospores were trapped pre- produced galls on 60 and 44% of the seedlings, respectively.
dominantly between 1000-2100 hr and were most abundant between Single aeciospore isolates from virulent single gall isolates
1600-1800 hr. Most conidia were trapped during the daylight appear to have great potential for determining variations
hours, particularly around midday. in virulence in the pathogen population and in resistance
among pine families.
229
233
THE INFLUENCE OF TEMPERATURE AND FRUIT AGE ON INFECTION
OF APPLE FRUIT BY VENTURIA INAEQUALIS. K. L. Reynolds and R. C.
Seem. Department of Plant Pathology, Comell University, New York State
Agricultural Experiment Station, Geneva, NY 14456.
COMPARATIVE VIRULENCE OF HETEROBASIDION ANNOSUM ISOLATES. F.
Cobb, Jr., T. Chase, W. Otrosina, A. Ratcliff, and T. Popenuck.
Dept. of Plant Pathology, Univ. of CA, Berkeley, 94720 and
USDA-For. Serv. Pacific Southwest Forest Exp. Station, Berkeley
Several studies have reported ontogenic resistance to V. inaequalis in apple fruit,
but none has observed the effects of this resistance on germination, appressorium
formation, or colonization. Attached and detached fruit were inoculated with
ascospores or conidia every 3 weeks beginning at petal fall. Attached fruit were
kept moist at ambient orchard temperatures for 1, 2, 4, 8 or 16 days. Detached
fruit were kept moist and incubated at 13, 22, or 31 C for 94 hr. Epidermal
sections were stained in cotton blue/lactophenol and examined microscopically.
The proportions of spores that had germinated, developed appressoria, and
successfully penetrated and formed a subcuticular stroma were recorded.
Temperature had a pronounced effect at all stages of infection. Fruit age did not
affect germination or appressorium formation, but the proportion of successful
penetrations decreased significantly as fruit matured. These results suggest that
ontogenic resistance is not due to inability of the pathogen to germinate or form
appressoria, but rather to inability of the fungus to penetrate the cuticle or an
interaction with the host that prevents formation of a subcuticular stroma.
No differences in mortality of white fir or ponderosa pine
seedlings inoculated with dikaryons and progeny homokaryons of
the 'S' and 'P' groups, respectively, were apparent but results
among homokaryons varied considerably. In another test, four
dikaryon isolates each of 'P' and 'S' and one of H. araucariae
from Australia were inoculated into seedlings of nine conifers.
All 'P' isolates were highly virulent on ponderosa and sugar
pines and less virulent on fir, Douglas-fir, Norway spruce,
giant Sequoia and western hemlock. The 'S' isolates were most
virulent on non-pine species and more variable than 'P' (one
was avirulent). The Australian isolate was moderately virulent
only on ponderosa pine, Sequoia, and Sitka spruce. Sitka
spruce was highly susceptible to all isolates and incense-cedar
was highly resistant to all isolates.
230
EFFECTS OF WATER STRESS ON WHITE FIR WOUND RESPONSE TO
TRICHOSPORIUM SYMBIOTICUM, FUNGAL SYMBIONT OF THE FIR ENGRAVER
SURVIVAL OF MUCOR PIRIFORMIS ON COLONIZED STONE FRUIT ENDOCARPS.
T. J. Michailides, Univ. of Calif., Berkeley, Kearney Agric.
Center, Parlier, 93648, and J. M. Ogawa, Dept. of Plant Pathology,
Univ. of Calif., Davis, 95616.
BEETLE. W. J. Otrosina and G. T. Ferrell, USDA Forest Service,
Pacific Southwest Forest and Range Experiment Station,
Berkeley, CA.
Effects of water stress on white fir reaction to stem
Sporangiospores of 1lucor piriformis attached to peach and
nectarine endocarps an opartially buried survived better in dry
(-1,300 1,300tbarn bars enari matric potend potential) partially soil buried than survve in wetd0.3bary
wet (-0.3
in
bar
mtests.
matric
potential) soil and longer at 0 and 10 C than at 27 and 33 C.
Sporangiospores declined over time in a polynomial (quadratic)
fashion in wet soil a all temperatures and in dry soil only at
33 C. The fungus grew and sporulated on endocarps incubated at
0, 10, and 21 C but not at 27 or 33 C. Washings from endocarps
induced germination of sporangiospores of M. piriformis (up to
50%) and increased its growth and sporulation. The decline of
M. piriformis propagules on endocarps buried in soil in a peach
orchard was exponential after the initial 5 mo. Chlamydosporelike
structures developed in mycelia and sporangiophores were
inoculation with the fungal symbiont of the fir engraver beetle
(Scolytus ventralis LeC.) were assessed in greenhouse and field
carried
Inoculum
by individual
was selected
beetles.
from surveys of fungal
Among
populations
the most prevalent fungi
recovered from beetle washings were Trichosporium symbioticum,
unidentified species of Cladosporium, Graphium, Paecilomyces,
Penicillium, and yeasts. In both greenhouse and field
inoculations with T. symbioticum, firs under high water stress
(xylem pressure potentials under -2.0 mPa) produced lesions
which were longer and less resinous than those of firs under
lower stress. The differential host reactions to this fungus
may be potentially useful in assessment of susceptibility
drought stressed white fir to attack by the bark beetle-fungus of
complex.
found in decayed tissues. More than 75% of the colonies of M.
piriformis recovered from propagules on endocarps originated
from sporangiospores.23
NUCLEI IN NATURE AECIOSPORES FRON TWO ZYNODENES OF PERIDERMIUM
231 HARKNESSII IN CALIFORNIA. 0. R. Vogler, F. W. Cobb, Jr., and
231 L. Epstein, Department of Plant Pathology, University of
INTERFERTILITY OF '5' AND 'P' GROUPS OF HETEROBASIDION ANNOSUM California, Berkeley, CA 94720.
IN NORTH AMERICA. T.E. Chase, W.J. Otrosina, and F.W. Cobb, Jr.
USDA-Forest Service, Pacific Southwest Expt. Sta. P.O. Box 245, We used epifluorescent microscopy to count nuclei in aecio-
Berkeley,CA 94701 and Department of Plant Pathology, University spores from two zymodemes (electrophoretic types) of Peniof
California, Berkeley, CA 94720. dermium harknessii J. P. Noore. For each single-gall isolate,
spores were fixed overnight at 4C in 3.7% formaldehyde,
pelleted by centrifugation, resuspended in 0.1 ug/ml 4,6-
H. annosum in North America consists of two biological species diamidino-2-phenylindole (DAPI) for 6 min, pelleted and rinsed
designated '5' and 'P. In experiments to be discussed with water 6 times, and mounted in 75% glycerol in 25% phosinterfertility
(% dikaryons formed) between groups in the phate buffer (pH 8). Nuclei were counted at 800X using filters
western U.S. was quantified as cm. 18%. Interfertility is not recommended for DAPI by the microscope manufacturer(Zeiss).
random but can be ascribed to presence of '+ intersterility Spores from zymodeme I (collected from several pine hosts
alleles in both groups. Thne distribution of intersterility throughout California) were predominantly (>75%) binucleate,
alleles, the nature of inter-group hybrids, their stability, while spores from zymodeme II (collected from lodgepole pine in
and significance in the pathology and speciation of the fungus the central Sierra Nevada) were predominantly (>85%) uniwill
be discussed. Isozymes provide additional markers for nucleate. Implications for the nuclear behavior of this
monitoring heterokaryon and dikaryon formation and stability, endemic forest pathogen are discussed.
1164 PHYTOPATHOLOGY
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