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54 58
YIELD CONSTRAINTS IN WHEAT DUE TO SOILBORNE PATHOGENS. PERSPECTIVES OF DISEASE THREAT IN LARGE-SCALE PINUS RADIATA
E.A. Milus and C.S. Rothrock, Dept. of Plant Pathology, MONOCULTURE -THE NEW ZEALAND EXPERIENCE. C.K.S.Chou, Forest
University of Arkansas, Fayetteville, AR 72701. Research Institute, Rotorua, New Zealand.
About 95% of New Zealand wood production today comes from exotic
The importance of soilborne pathogens as constraints to plantations (mainly Pinus radiata) .For over 6 decades this forestry
wheat yield and quality in Arkansas was determined in a monoculture,now 1.1 million hahas withstood the threat of dissplit,
strip plot experiment. Main plots were raised or ease. In the late 1940's 25-35% of 20-25-year-old trees (unthinned
conventional seed beds. Subplots were fumigated (Bromogas stands) were killed in a Sirex-Amylostereum epidemic.However the
67), metalaxyl-treated seed, and a nontreated check. Sub- economic loss was insignificant.Aerial spraying to control
subplots were planted with wheat (cv. Keiser, Florida 302, Dothistroma needle blight since 1966 has cost around $14.5
or Caldwell) or oats (cv. Bob). In January plants were dug million. Losses caused by other diseases, i.e.,Sphaeropsis sapinea
from the ends of each plot, growth parameters were measured, Armillaria root-rot,and Cyclaneusma needle-cast, have been
and the entire crown and root system plated onto water agar. locally severe but tolerable overall. The current practice of waste
Fungal colonies were transferred to PDA, identified to genus, thinning 75- 8 5% of initial stockings before age 10-12 allows a high
and representative isolates were tested for pathogenicity. level of acceptable loss for diseases which mainly attack young
Bedded plots had twice the number of plants infected with stands, while clear-felling at age 25-30 obviates diseases that
Helminthosporium sativum. Plants from fumigated plots had affect older stands.However, New Zealand still has only a few pine
more tillers/plant, greater top weight, and fewer plants pathogens and with the trend towards clonal forestry, genetic uniinfected
with Pythium, Helminthosporium sativum, and formity, and reduction of initial/final crop stocking ratios,the
Rhizoctonia. Pythium was the most commo .genus isolated. history of disease in this country is no way near its end.
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HYPOVIRULENT STRAINS OF CRYPHONECTRIA PARASITICA IN
RECOVERY
NEW JERSEY.
OF WHITE AND GREEN ISOLATES OF ASPERGILLUS FLAVUS P.J. Bedker. Department of Horticulture
FROM
and
INDIVIDUAL
Forestry,
KERNELS
Rutgers
FROM DOUBLE-INOCULATED MAIZE EARS. University, New Brunswick, NJ 08903.
Natale Zummo, USDA-ARS, Dept. of Plant Pathology and Weed
Science, Mississippi State, MS 39762. Approximately 30 isolates of C. parasitica were collected from
cankers
Maize on ears were
American chestnut inoculated at 4 locations. in the field The with virulence a white of
each was determined by inoculating
isolate of
"Granny
Aspergillus
Smith"
flavus
apple
at
fruits.
2 days after midsilk in Mean radial growth (MRG) was determined
the shank or
by
through
measuring
the
the
husk
length
in the base of the cob and and width of lesions at 17 days after inoculation for 8
re-inoculated 4 days later with a green isolate of the replications / isolate. Each apple was also inoculated with
fungus through the husk at the top
silk
of the
channel.
ear or in the
Reciprocal
strain
inoculations
EP155 from Connecticut.
were made.
The MRG
Ears
for isolates collected
from sites in Howell and Millstone Twps.
were
(Monmouth
harvested at
Co.),
60 days after midsilk, dried, and Plumsted Twp. (Ocean Co.), and Sandyston Twp. (Sussex
shelled. When
Co.)
kernels
were
from these double-inoculated ears 18.2, 19.1, 17.3, and 18.4 mm, respectively. The
were
MRG for
assayed,
37.5
the
%
white isolate was recovered singly from (45/120) of the isolates was significantly
8% of kernels,
(P