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324
NUCLEAR NUMBER AND BEHAVIOR IN SCLEROTINIA SCLEROTIORUM. E. J.
Ford, D. C. Sands, and K. Adkisson, Dept. of Plant Pathology,
Montana State University, Bozeman, MT 59717.
was only partially effective on strawberry. Both mixtures
increased dicarboximide resistance. Thiram or chlorothalonil
useo alone did not provide satisfactory crey mould control hut
did decrease the incidence of dicarboximide resistant strains.
Fluorescent microscopy was used to study nuclear number and
behavior in asci, ascospores, germinating ascospores, hyphae,
protoplasts and microconidia of S. sclerotiorum. Specimens were
stained with hydroethidine, DAPI, propidium iodide, Hoerst, and
calcofluor either singly or in various combinations to reveal
details of nuclear number, meiosis, mitosis, and cell wall
development. Classical patterns of meiosis were observed in
asci with 8 nuclei being formed followed by wall formation and
then a final nuclear division to yield two nuclei per mature
ascospore. Nuclear division in ascospores was evident after 2
hrs incubation in a nutrient broth at room temperature, which
was prior to germination of the ascospores. Young sporelings
had up to 16 nuclei prior to cross wall formation. A nuclear
generation time of ca. 2.4 hrs was determined for sporelings.
Hyphae from young shake cultures had 20-30 nuclei/cell,
Spheroplasts formed from active hyphae averaged 3.5 nuclei per
spheroplast. Microconidia were uninucleate.
328
HYBRID PERFORMANCE AND YIELD LOSSES ASSOCIATED WITH GRAY LEAF
SPOT DISEASE OF CORN IN VIRGINIA. P. J. Donahue and E. L.
Stromberg, Departments of Agronomy and Plant Pathology, Phy
Strog, departments of Alant PA Phy-
siology and Weed Science, VPI&SU, Blacksburg, VA 24061-0331.
Commercial corn hybrids were evaluated for 7 years at Wythe and
Shenandoah Counties and 1 year at Montgomery Co. under field
conditions for response to gray leaf spot disease, caused by
Cercospora zeae-maydis. Plants were scored 3 times during
the growing season. Disease severity indices were regressed
against grain yield and harvest moisture, and lodging by location
and year. Significant grain loss due to disease occurred in 2
of 6 years at the Shenandoah Co. site and 1 of 6 years at the
Wythe Co. site. A significant increase in lodging occurred in
325
ON HOST FAMILIES AND GENERA OF PERONOSPORA AND PLASBMOPBA
DOWNY MILDEWS AND ON GEOGRAPHIC PROCLIVITIES OF THE PATHOGENS.
R.Kenneth, Hebrew Univ. Fac. of Agric., Rehovot 76100, Israel
2 of 6 years at the Shenandoah Co. site and 5 of 6 years
at the Wythe Co. site. These data represent the effects of C
zeae-maydis
tial.
on a range of genotypes
The
differing in yield poten-
fact that significant associations occurred indicate
the strong effect gray leaf spot can have when environmental
conditions are favorable.
Data from host-downy mildew (dm) check-lists provided information
on the two most common genera of Peronosporaceae. Of the
ca 51 host families with Peronospora, 8 are stricken in single
countries only; of the 22 with Plasmopara, at least 4. Despite
a dearth of dms of these genera in the tropics, a few thrive
e.g. Plasmopara on Vitaceae and Peronospora on Euphorbiaceae,
the latter unrecorded in cold regions. Australia and New
Zealand have few dms: 3 and 10 host families respectively with
PeronosPora and 1 and 2 with Plasmopara (vs 34 in Romania with
Persnoanora and ca 17 in USA and 9 in Canada with Plasmopara).
Although Plasmopara is recorded on only 7 families in Britain
and 8 in France, there are 20 and 26 host genera of Umbelliferae
vs only 4 and 2 in USA and Canada (and none in the east
Mediterranean Basin). For Plasmopara on Asteraceae, however,
there are ca 20 host genera in USA vs none in Britain and 4 in
France. Of the 33 legume genera with Peronosl.ora, 8 are in
single countries only e.g. Cicer in Israel, yigna in USA.
326
SCLEROTINIA BLIGHT OF PEANUT IN TEXAS: OCCURRENCE AND DETECTION
OF THE PATHOGEN IN SEED. R.A. Taber, D.H. Smith, J. S. Neck,
S.L. Segner, D.M. Porter, D.H. Lewis, and T.M. Omran. Dept. 329
Plant Path. & Micro., Unierity tatonandYokum Tx. Cllee Agri. Exp. Sta., T;; Texas SD, AS, A&M EVALU]ATION OF MEIHDSFOR SAMPIG, RIECOVERY
University,
AND
College Station
ENUMERATION
and
OF
Yoakum, Tx.;-USDA, ARS, BAC IA APPLIED TO THE PHYLLOSPHERE. Q. A. MatyacI, K.
Suffolk, Va.; and Vet. Micro., TAMIU, College Station, Tx. 77843 Donegan , R. Seidler 2 , V. Prince 1 and A. Porteus2. N.S.I.
Peanut Sclerotinia blight was first observed in Texas in Mason Technology ServicesI and E.P.A.2, Corvallis Environ.ental
County in 1981 on cv. 'Florunner'. Since 1981 it has been Research Laboratory, Corvallis, OR. 97333.
observed in other counties in Texas. The role of seed in Erwini herbicola or Enterobacter cloacae were sprayed on oa
propagule dispersal is currently under study. Sclerotia were orwin le a Bacteri ac te r oaca e le af a nd bulk
observed in infested seed; however, the incidence was less than or bean leaves. Bacterial Counts from single leaf and bulk
1%. In spite of seed shriveling and discoloration, leaf samples were similar 1-7 days after application, bit after
germinability and emergence from infested seed exceeded 90%. 14-35 days Counts from bilk samples were significantly larger.
Presence of the pathogen was successfully detected in seed Butlk sample values could be adjusted to those of mingle leaves
using the Agri-Diagnostics Inmunoassay Kit and serial using estimates of the single leaf varianc. More bacteria
sectioning. The pathogen was most prevalent in the peanut were remo~ved by stomacher blending than sonication, blending,
testa. Fluorescein isothiocyanate-labeled monoclonal antibodies or washing leaves in biffer. Stomacher blendling was reliable
developed from an isolate of Sclerotinia from Texas peanuts ovrawdrngofbceilppatnsndhn2-0%f
permitted localization and verification of specific hyphae of t)he Leaf sample carried bacteria. The surface drop technique
the pathogen in the seed with the aid of immunofluorescence, f~r enumerzation of bacteria uses four 10 ul aliquots and showed
nO cifferene from the 100 ul aliquot spread plate method.
,These methods proved to be rapid, efficient and precise in
327 estimating parametera of bacterial populations.
INFLUENCE OF SPRAY SCHEDULES O)N RESIST/GIT POPULATIONiS OF BOTRY-
TIS CINEREA. M.L. GULLINC, C. ALDI and A. GARIBALDI Istituto di 330
Patologia vegetale, Via Giuria 15, 10126 Torino, Italy.
In the presence of benziinidazole and dicarboximide resistant
strans cnera f Btryts Pes. nd f hih dseae inidece,
treatm~ents with di carboximides provided only partial control of
grey mould on grape, strawberry and tomato and increased the
percent of dicarboximide resistant strains. The combination of
a benzimidazole with diethofencarb (alternated or not with a
dicaooxinie) dicaboxmid) stisactry
atifactry povied
oovied ontol
ontol o
f
gry
gry
muldand
muldand
decreased the percent of benzimidazole resistant strains. The
mixture of procysidone with thiran controlled grey mould of
grape, while the combination of orocymidone and chlorothalonil
DIFFERENTIATION OF TOMATO RACES 1 AND 2 OF VERTICILLIUM DAHLIAE
USING VEGETATIVE COMPATIBILITY ANALYSIS. T. R. Joaauim and R.
C. Rowe, Dept. of Plant Pathology and W. A. Erb, Dept. of
HriutrOi tt nvWotr H461
Sixteen strains of Verticillium dahliae, designated as either
tomato races 1 or 2, were tested for vegetative compatibility.
Compatibility was assessed by pairing complementary, nitrate-
mutants
nonutilizing
of tester
(nit)
strains
mutants
representing
derived from each
several
strain with
vegetative
nit
compatibility groups (VCGs) (Phytopathology 73:1305-1308). Nit
mutants were isolated from each wild-type strain by selecting
for chlorate resistance on corn meal agar with dextrose (Difco)
1176 PHYTOPATHOLOGY