PURDUE UNIVERSITY
Departments of Agronomy, Entomology, and Botany and Plant Pathology,
and USDA-ARS, West Lafayette, IN 47907, USA.
H. Ohm, J. Anderson (USDA-ARS), W. Berzonsky, I. Dweikat, D. McFatridge, F. Patterson, and H. Sharma (Department of Agronomy); G. Buechley, S. Goodwin (USDA-ARS), D. Huber, K. Perry, and G. Shaner (Department of Botany and Plant Pathology); S. Cambron, F. Maas, R. Ratcliffe, R. Shukle, and C. Williams (USDA-ARS), and J.J. Stuart (Department of Entomology).
Production.
Farmers in Indiana seeded 700,000 acres (283,400
ha) of soft red winter wheat in the fall of 1994. The harvested
wheat area of 660,000 acres (267,206 ha) in 1995 was up 5 % from
1994. Total production in 1995 was 39.6 million bushels (1.08
million metric tons), up 3 % from production in 1994. Clark,
seeded on 15.4 percent of the wheat acreage, remained the leading
winter wheat public cultivar in Indiana in 1995. The cultivar
Cardinal ranked second, seeded on 8.9 % of the winter wheat acreage.
The average yield, despite several disease problems, was 60.0
bu/acre, compared to 61 bu/acre in 1994. Private brands and cultivars
occupied 65 % of the state's wheat area, up from 52.1 % in 1994
and 43.4 % in 1993. The northeast and southwest sections of the
state continue to be the major wheat-producing areas (Data source:
Indiana Agricultural Statistics Service, Purdue University).
Wheat diseases were severe in 1995. The extended
warm autumn of 1994 was conducive to infection by wheat spindle
streak virus and wheat soilborne mosaic virus. Warm autumn weather
also gave aphids time to multiply on the new wheat crop, and some
of these transmitted barley yellow dwarf virus. Symptoms of all
three diseases appeared early in the spring as the wheat resumed
growth after winter dormancy. The frequent rainfall during April
and the first half of May provided moisture for production of
inoculum and infection of mature plant tissues by various pathogenic
fungi. The weather was cooler than normal during stem elongation,
so these diseases did not develop rapidly. Symptoms were confined
mostly to the lower leaves, and the dense canopies, resulting
from good autumn growth and good winter survival, made the wheat
crop look very good. Powdery mildew was reported from some regions
of the state, but was not a major problem. Later in May, the
weather became warmer, yet it continued wet. Septoria blotch
(Septoria tritici), Stagonospora blotch (Septoria
nodorum), leaf rust, and scab developed to moderate and
severe levels during grain filling, and the crop deteriorated
rapidly. Puccinia recondita usually does not survive
winters in Indiana, but did in 1994-95 because of the unusually
mild winter. Also, leaf rust was severe in the southeast U.S.
in the early spring, and southerly winds carried spores north
where the frequent rainfall in Indiana provided the leaf surface
wetness necessary for infection. Thus, rust became established
in the crop in Indiana earlier than normal, and symptoms progressed
rapidly.
Although weather conditions in 1995 were not conducive
to production of high yields of good quality soft wheat, they
were especially favorable for selection in the breeding program.
Severe epidemics of Septoria and Stagonospora blotches, leaf
rust, and scab allowed us to select lines with superior resistance.
Since Stagonospora blotch (= Septoria nodorum blotch)
became an important problem in the mid-1980s, we have identified
sources of resistance, particularly from South America and Europe,
and incorporated these into elite soft red winter wheat lines.
Many of these lines looked excellent for resistance this year
and also had good agronomic characteristics, plus resistance to
other diseases. Among breeding lines in various yield trials,
we found excellent levels of resistance to powdery mildew, leaf
rust, and soilborne mosaic virus; good levels of resistance to
Septoria blotch; and Stagonospora blotch, and what appears to
be a useful level of `low incidence' of scab, even
though a specific source of scab resistance is not in the pedigrees
of these lines. The most encouraging observations were for resistance
to Septoria and Stagonospora blotches. Under conditions in which
all four stem leaves of susceptible checks were killed, symptoms
were absent from the upper two leaves on many of these lines.
Seed of cultivar `Patterson'
is being increased and should be available for distribution to
seed producers after harvest in 1996. Patterson is early-maturing
like Clark; is very cold hardy; has excellent soft wheat milling
and baking qualities; and has resistance to leaf rust and soilborne
mosaic virus, but is moderately susceptible to powdery mildew.
(Ohm et al.)
To develop durable protection against leaf rust,
we are studying partial, quantitative resistance, termed slow-rusting.
Slow-rusting should be durable, because it does not entirely prevent
rust and, therefore, places less selection pressure on the pathogen
for evolution of new, more virulent races. In 1995, we completed
the second year of a field study of slow-rusting in 104 F8 lines
derived from a random sample of the F2 of the cross `CI 13227/Suwon
92'. CI 13227 is slow-rusting and Suwon 92 is highly susceptible.
Earlier studies of this population in the greenhouse showed that
the long latent period of CI 13227 (13 days compared to 7 days
for Suwon 92) is conditioned by four epistatic genes of unequal
effect. A wide range in rust susceptibility occurred among F8
lines. At maturity, some had only 14 % rust (CI 13227 had 19
%), whereas others had 84 % (Suwon 92 had 75 % rust). Many families
had values somewhere between these extremes. In this cross, slow
rusting does not appear to be associated with tall plant type,
late maturity, or susceptibility to powdery mildew (CI 13227 traits),
so it should be possible to transfer slow-rusting to early-maturing,
short-statured wheats with mildew resistance. These results also
show that slow-rusting can be selected reliably in breeding nurseries
in the field. A slow-rusting line that is selected in a breeding
nursery will have less rust when grown in a pure stand, where
it is not inundated with rust inoculum from nearby susceptible
plants, as occurs in a breeding nursery.
In collaboration with Dr. Anne Desjardins and colleagues
at the USDA-ARS National Center for Agricultural Utilization Research
in Peoria, IL, we tested a mutant strain of the scab fungus for
its ability to cause disease. This strain was altered specifically
so as not to produce DON, the toxin that causes feeding problems
in swine, other animals, and humans. The toxin previously was
not thought to be involved in development of the disease in wheat
and barley. Results of our field studies showed that the mutant
was much less pathogenic on wheat. The significance of this finding
for disease control is that it might be possible to develop wheats
that prevent natural strains of the fungus from producing toxin
or that break down the toxin once it is produced. This then could
confer resistance to scab. (Shaner and Buechley)
Barley yellow dwarf viruses (BYDV).
New serotypes of BYDV appeared in Indiana in the 1994-95 season. The RMV serotype was observed at multiple sites in the state and had not been reported previously; there was one unconfirmed report of the SGV serotype. Mixed infections were quite common. Of 25 symptomatic plants sampled in Tippecanoe County, 17 (68 %) contained two or more of the BYDV serotypes PAV, RPV, or RMV. The severity of natural infestations of BYDV provided ideal conditions to monitor the stability of BYDV resistance from a wheatgrass plant. Plants from field plots of cultivar Patterson and from a wheat substitution line, P29, carrying one wheatgrass chromosome and the wheatgrass-derived BYDV resistance were sampled in a non-randomized, structured fashion. In plots of Patterson, 48 % (n = 42) were infected with either the PAV, RPV, or RMV serotypes of BYDV. In contrast, only one of the plants in the P29 plots was infected. This plant was likely an `off-type', because the PAV isolate recovered from it was able to infect test cultivars not carrying the resistance from wheatgrass. Still, it was not able to infect P29 or other lines carrying the wheatgrass resistance. (Perry)
A recombinant inbred population, developed by hybridizing
a line carrying resistance of cultivar Roazon to an advanced Purdue
line, was screened for resistance to glume blotch. A total of
171 F5 families was screened in the greenhouse in autumn 1994.
Approximately 18 % of the families were selected as uniformly
susceptible and 18 % as uniformly resistant based on leaf and
spike necrosis ratings. Using remnant seed, the same 171 families
were planted to the field in autumn 1994 and evaluated for glume
blotch under a severe natural infection in 1995. The progenies
(F6 plants) of the selected families, tested in the greenhouse
in autumn 1994, were evaluated in greenhouse tests in the spring
of 1995. From these evaluations, four families each, which were
uniformly either susceptible or resistant, were selected and are
being evaluated again for glume blotch severity in the greenhouse.
Our goal is to identify molecular markers associated with glume
blotch resistance. (Berzonsky and Ohm)
Hessian fly resistance gene H9.
To map the Hessian fly resistance gene H9
in wheat, we have identified four DNA markers closely linked to
H9. An F2 population of 1,200 plants from the cross, `Newton
(susceptible)/Iris (H9H9)' and near-isogenic to
Newton, was developed. We have tested for recombinants using
only the susceptible F2 plants (300 plants). The four markers
were placed at 0.67 cM (closest marker) to 4.3 cM (farthest marker)
from H9. We are initiating physical mapping efforts in
this region. (Dweikat and Ohm)