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oriented trajectories, with the receptor point located in the mountains of North Winter oilseed rape (Brassica napus) grown on 17'000 ha is
Carolina, were calculated for April through August and for the annual period. the predominant edible-oil crop in Switzerland. The moat
The 12-, 24-, and 48-hr air parcel positions prior to arrival at the receptor point important fungal diseases are caused by Phoma lingam, Alterwere
analyzed by examining the plots of the probability density function (pdf). naria sp., Botrytis cinerea and Sclerotinia sclerotiorum.
By integrating the pdf over a region of interest the probability that the given Cylindrosporium concentricum, Verticillium dahliae and Pseureceptor
site will receive air parcels from this region can be obtained. Results docercosporella capsellae are rarely found but have the
indicate that the probability of the receptor point receiving air parcels from the potential to become more prevalent.
tobacco producing region of south Georgia/north Florida, which is a potential Integrated crop management is employed to try to control
inoculum source region, increases during the April to August period. This these diseases. It involves measures such as use of resistant
increase can be attributed to the strengthening of the Bermuda high pressure cultivars, crop rotation and removal of infected residue.
system. Fungicides are considered a last resort. None are registered
at present. The identification of resistant cultivars is a
top priority in our research. Special nurseries have been
established. The potential use of biotechnology for this
7 purpose will be investigated.
GENETIC DIVERSITY AND POPULATION STRUCTURE OF THE RICE
BACTERIAL BLIGHT PATHOGEN. J. Leach, M. Rhoads, C. Vera Cruzi,
F. White, T. Mews, and H. Leung . Dept. of Plant Pathology, 11
Kansas State University, Manhattan, Kansas and lInternational INFECTION OF STRAWBERRY ROOTS BY COLLETOTRICHUM
Rice Research Institute, Los Bafios, Philippines. FRAGARIAE AND GLOMERELLA CINGULATA. C. M. Howard, C.
A repetitive DNA element pJEL101 isolated from Xanthomonas K. Chandler, and E. E.. Albregts. Univ. of Fla., AREC,
campestris pv. oryzae (Xco) was used to determine the popula- Dover, FL 33527.
tion structure of Xco in the Philippines. pJELl01, when used Large roots ca 14 cm long were excised from rhizomes
to probe EcoRl-digested genomic DNA of Xco isolates, revealed of strawberry plants that had wilted in Florida
race-specific restriction fragment length polymorphisms (RFLP). fruiting rields because of anhthacnose crown rot.
Of 94 isolates examined, 26 RFLP types were identified. Most Isolations from the thizomes yielded primarily C.
of the variability (20 RFLP types) was found in race 1, 2, and fragariae from seedlings that previously had bean
3, which were isolated from lowland areas. Three RFLP types grown n a Florida nursery and G. cingulata ( = C.
were found among isolates from traditional cultivars grown at gloeosoorioides) from Chandlec p-ans that previoaly
high elevation. The genetic diversity of the total Xco popula- had been grown in a Tennesse.e nursery. The roots were
tion was 0.93, of which 44% was due to genetic differentiation cut into 1 c.m sections and every other, section
between races. The genetic diversities of isolates collected beginning with the basal section was plateC on PDA.
in 1972-1976, 1977-1981, and 1982-1986, were 0.89, 0.89, and Colletotrichum spp. or G. cingulzta (primarily C.
0.91, respectively, suggesting a consistently high level of fragariae fros seedlingY, and . cinngulata and C.
variability in the pathogen population over the past 15 years. acutatum from Chandler) were isolated from 45% of the
basal root sect ions and from 11% of 'he thi]cd
sections. These fungi were isolated from 1.4% to 2.&%
8 of sections 5, 7, 9, 11, and 13.
CULTURAL CONTROL OF SCLEROTINIA CROWN AND STEM ROT IN
ALFALFA SEED FIELDS. R, G, Gilbert, USDA-Agricultural 2
Research Service, P. 0. Box 30, Prosser, WA 99350.
Cultural control of Sclerotinia in broadcast-planted alfalfa A 72KD PROTEIN ASSOCIATED WITH CERCOSPORIN SYNTHESIS IN
seed fields were: 1) "fall-burn" of harvest residue; 2)
"winter-burn"; and 3) "spring-beat-back." Fall-burn reduced
CERCOSPORA KIKUCHII TOXIGENIC ISOLATE PR. Jeffery A. Rollins
and Robert C. Upchurch. Department of Plant Pathology, N.C.
sclerotia in the field by >95%. Sclerotia were killed in State University, Raleigh, NC 27695-7616.
the residue and surface soil. Only 14% of the surface soil
sclerotia were viable after the fall-burn in November and Comparative SDS-PAGE analysis of the protein extracts of C.
during the next 6 months the number of surface soil kikuchii parental isolate PR and cercosporin-minus mutants
sclerotia declined from 246/m2 to 7/mi, and the viability of derived by UV mutagenesis from this isolate revealed that a
sclerotia was reduced from 12 to 0%. Winter-burn reduced prominent 72kD protein present in the parental isolate was
surface residue and sclerotia numbers, but did not reduce absent in the mutants. Two-dimensional gel electrophoresis
viability and survival of surface soil sclerotia. Spring- indicates that the protein is basic. Gel scans indicate that
beat-back dried the soil surface and reduced the canopy the protein composes as much as 12% of the total extractable
relative humidity, which established conditions that were protein of PR, but that it is present in lower concentration in
unfavorable for Sclerotinia activity. Alfalfa seed yields other Cercospora species. Temporal analysis of toxin and
in the fall-burn and spring-beat-back treatments were 862 protein synthesis in PR shows that the 72kD protein is
and 716 Kg/ha for an increase of 43 and 13%, respectively, positively correlated with the synthesis of cercosporin. We are
over winter-burn, interested in identifying this protein by cloning and
characterizing its encoding gene because of the possibility of
its involvement in cercosporin synthesis and/or regulation.
9
CONTROL OF PHYTOPHTHORA ROOT ROT ON CITRUS WITH SODIUM
TETRATHIOCARBONATE. N.E. Natheron and J.C. Natej ka,
1
Univrsiy ofArionaYum Agrc. ente, Yma, Z 8364CHARACTERIZATION OF HYDROXAMATE SIDEROPHORES AND SIDEROPHORE-
Greenhouse studies were initiated to determine the efficacy of -MEDIATED IRON IN GAUMANNOMYCES GRAMINIS VAR TRITICI. S. DoniI,
sodium tetrathiocarbonate (STTC) for control of root rot on S. Solel 3 , Y. Kashman 2 and I. BarashI, Dept. of 3 plant Pathology,
citrus caused by Phytophthora citrophthora and _P. parasitica.
When roots of rough lemon seedlings were inoculated with
ARO, The Volcani Center, Israel.
zoospores of these two fungi in the presence of STTC at 245
pg/al or metalaxyl at 10 pg/al, resultant fresh weights of
Under iron-deficient conditions Gaumannomyces graminis var
tritici (Ggt) produces hydroxamate siderophores designated as
shoots and roots did not differ from noninoculated plants, A, B and C according to their electrophoretic mobility. Siderowhereas
inoculated plants without chemical treatment suffered phores B and C were identified as dimerum acid and coprogen B
significant loss of shoot and root weights. Treatment with STTC
at 4900 pg/al was necessary to inactivate propagules of
respectively. Siderophore A exhibited and identical NMR spectra
to dimerum acid but was chromatographically distinct. The system
P. parasitica in naturally infested soil. Rough lemon seedlings of siderophores mediating uptake of iron was characterized. It
planted 7 days after treatment of soil to avoid phytotoxic exhibited an active transport and Michaelis kineties. Ggt could
levels of STTC had root and shoot weights equivalent to those utilize iron effectively from siderophores produced by other
grown in soil treated with 10 pg/ml metalaxyl. Apparently,
can reduce the severity of root rot on citrus caused by
STTC fungi. Competition experiments between coprogen B., dimerum
acid and hydroxamate siderophores from other structural classes
P. citrophthora and _P. parasitica, suggest a common transport system. Wheat seedlings were capable
of utilizing iron from coprogen B and dimerum acid. The role of
siderophores in survival and virulence of Ggt will be discussed.
10
CONTROL OF FUNGAL DISEASES OF WINTE OILSEED RAPE IN SWITZER-
LAND. M. W. Andrea and W. E. Winter, Swiss Federal Research Highly virulent isolates of Fusarium selani from soybeans produce the Nectria ascoma
Station for Agronomy, Reckenholzstr. 191, 80146 Zuerich, stage. T. S. Abney, T. L. Richards, A. J. Ivanovich, & D. H. Scott. USDA-ARS and
Switzerland. Purdue University, W. Lafayette, IN 47907.
1136 PHYTOPATHOLOGY
14