Early-planted wheat diseases and management.
Experiments were conducted at four locations to examine
the effect of chemical seed treatments and cultivars on yield,
heading, and disease and insect development on wheat planted early
(3-4 weeks) versus on a normal date. The objective is
to develop strategies to permit earlier planting in order to avoid
wet soils at the recommended planting dates, without increasing
freeze, insect, and disease damage. Wheat cultivars tested were
FFR 525, Coker 9835, and Pioneer 2566. Chemical seed treatments
were: Gaucho (imidacloprid) vs none and Vitavax 200, `Baytan
+ Captan', or no fungicide in a `2 x 3' factorial.
The early date of this study actually resulted in a 370 kg/ha
higher average yield than the normal date. Gaucho significantly
reduced aphid counts, but resulted in only a slightly higher grain
yield.
Neither fungicide regimen had an effect on grain
yield when leaf rust was present. An early date of the wheat
variety trials also was evaluated to determine which varieties
are most adapted to early planting. The average yield of 23 entries
in this test was 343 kg/ha less for early vs normal planting dates.
Agratech/FFR502W, Pioneer 2684, and several other entries had
excellent and similar yields at both dates and showed little effect
of planting date on heading date. These lines probably have a
minimal vernalization requirement and a strong photoperiod response.
Contrary to the preconceived belief, no relationship occurred
between actual heading date and tolerance of early planting.
Some of the later-heading varieties showed a yield decline when
planted early, and some of the early-heading varieties showed
a yield increase when planted early.
Results from a combined analysis of variance showed
a significant difference between planting dates for leaf rust,
bacterial leaf streak, Septoria glume blotch, and for total number
of pustules on 10 wheat seedling plants. Early planting resulted
in higher ratings for leaf rust, Septoria glume blotch, and bacterial
leaf streak. However, the total number of aphids and yield responses
(bushel/acre) were not influenced by planting date. Differences
in varieties were observed for leaf rust bacterial leaf streak,
Septoria leaf and glume blotch, total number of pustules, and
yield. Of three cultivars tested, FFR 525 was the most diseased
and lowest yielding cultivar. Pioneer 2566 had the lowest incidence
of leaf rust and Septoria leaf and glume blotch. Chemical seed
treatment affected only aphid populations in Louisiana. Consistent
interactions between planting date and cultivars were observed
for Septoria glume blotch, leaf rust, and total number of aphids.
The area under the rust progress curve (AURPC) was correlated
inversely with yield and bacterial leaf streak. (Harrison, Tubajika,
Russin, Whitehead)
Soil fertility practices to maximize wheat yield potential.
Wheat profitability depends on fertilizer management
and the control of foliar diseases. Optimal N rates depend to
a large extent on soil type, with fine-textured soils requiring
higher N rates than coarser-textured soils. The availability
of other plant nutrients, i.e., K and P, also may vary depending
on soil texture. For example, soil K often is low on loessial
silt loam soils and relatively high on alluvial soils, especially
clay soils. Plant nutrients may have some influence on the development
of wheat diseases. Research has shown that excess N and deficient
soil K may result in increased disease levels. In recent years,
incidence of leaf rust has been noticeably higher on the loessial
soils of the Macon Ridge than on the Mississippi River Delta soils
in northeast Louisiana. One possible explanation for this is
the extremely low soil K levels on the loess-derived soils of
the Macon Ridge area. If expensive fungicides are required to
control diseases, profitability of wheat may be reduced substantially.
Some of the new cultivars respond to high N rates and have varying
levels of disease resistance. Information is needed on the N,
K, and P requirements of newly released cultivars. Also, the
interaction of disease development and plant nutrition needs to
be better defined. An experiment was conducted in 1995 on a loessial
silt loam on the Macon Ridge evaluating two wheat cultivars at
varying N, P, and K rates. According to soil tests, K was very
low and P was low. In 1995, yield responses to fertility rates
were minimal. Disease pressure also was extremely low in 1995.
This study will be continued in 1996. (Mascagni, Harrison)
About 350 new crosses were added to the LAES wheat
breeding program in 1995. About half of these were three-way
or top crosses. A gravity table was used to screen/clean increase
plots and F2 populations in 1995. Future F2 populations will
be combine-harvested and run over a gravity table. The heaviest
25 % will be used to plant bulk F3 populations, from which superior
heads will be selected for head rows. A set of bulk F2 and F3
plots was planted approximately 1 month early to select for photoperiodic
types. A system will be established whereby alternating generations
are planted first earlier, then later than normal to select for
genotypes that have stable heading dates regardless of planting
date. Three lines were advanced to the USDA Uniform Southern
Soft Red Winter Wheat Nursery.
The recurrent selection based on Ms3 is ongoing.
Populations have been through about 10 cycles of open-ended
recombination and selection. They have been selected for multiple
disease resistance and agronomic adaptation. Seed of elite sterile
plants are used each year to form the next population, and elite
fertile plants are advanced to F2 bulk plots. A new population
will be initiated for waterlogging tolerance in 1996. If you
are willing to share genotypes that might have tolerance to full-season
waterlogging, please contact Steve Harrison. Resulting populations
will be made available to all breeders. (Harrison, Thompson,
Seale)
Publications.
Harrison SA, et al. 1995. Performance of small
grain varieties in Louisiana, 1994-95. LAES Mimeo Series 106:1-74.
Harrison SA, LaBonte D, Johnson C, Linscombe S, Milligan
S, Myers GO, Oard J, and Venuto B. 1995. Plant breeding and
genetics: an investment in the future of farming. Louisiana Agric
38(2):14-21.
Tubajika KM, Russin JS, Clark CA, and Harrison SA.
1995. Spread of Xanthomonas campestris pv translucens
in wheat studied with a rifampicin resistant strain. Phytopath
85:1189.
Tillman BL, Harrison SA, Russin JS, and Clark CA.
1996. Relationship between bacterial streak and black chaff
symptoms in wheat. Crop Sci 36:74-79.
Tillman BL and Harrison SA. 1996. Heritability
of resistance to bacterial streak in winter wheat. Crop Sci 36:412-418.
Tillman BL, Harrison SA, Clark CA, Milus EA, and
Russin JS. 1995. Evaluation of bread wheat for resistance to
bacterial streak. Crop Sci 36:In Press.