Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

56
Diallel Analysis of Septoria Tritici Blotch Resistance in
Winter Wheat
X. Zhang, 1 S.D. Haley, 2 and Y. Jin 1 *
1 Plant Science Department, South Dakota State University, Brookings, SD, USA
2 Department of Soil and Crop Sciences, Colorado State University, Fort Collins, CO, USA
Abstract
In the winter wheat area of the northern Great Plains, leaf spot complex has been problematic in the past decade. In years
with high precipitation from late April to July, septoria tritici blotch (STB), caused by Septoria tritici, is most prevalent. As
part of our effort to improve STB resistance, inheritance of STB resistance was investigated by an eight-parent full diallel
scheme. Parents, F 1 , and reciprocal F 1 were planted on three different dates. Within each planting date, three to five seeds of
each experimental unit were planted in the greenhouse. Materials were arranged in a randomized complete block design
(RCBD) with three replicates. Plants at the second-leaf stage were inoculated with a bulk of six S. tritici isolates. Significant
general combining ability (GCA), specific combining ability (SCA), and reciprocal effects were observed in the analysis of
variance. The ratio of GCA sum of squares relative to SCA sum of squares suggested that GCA was more important than
SCA. Additive effects played the major role in host response to STB, while non-additive effects were also detected. General
combining ability effects of individual genotypes were in close agreement with parental performance. KS94U338, a genotype
with resistance derived from Triticum tauschii, had the lowest STB score and the highest general combining ability. This
result indicates that this genotype, possessing resistance distinct from other known sources, should prove useful in breeding
efforts to improve STB resistance in wheat.
Winter injury is the most
adverse factor for winter wheat
production in the northern Great
Plains of the USA. Adoption of
conservation tillage practices, with
winter wheat planting into spring
wheat stubble, has increased
steadily over the past decade.
While this practice improves winter
survival, accumulation of wheat
residue on the soil surface has
promoted the development of leaf
spot diseases in this region. Severe
epidemics of leaf spot complex on
winter wheat have occurred during
the last decade. Septoria tritici
blotch has been predominant in
years with above average
precipitation from late April to July.
Improvement of STB resistance was
intensified in our project beginning
in 1995. As part of this effort, we
initiated studies to investigate
combining ability of STB resistance
* First author prevented from attending
workshop by unforeseen travel
problems.
in known resistant genotypes. A
better understanding of resistance
could lead to more efficient
deployment of germplasm
resources.
Materials and Methods
Eight winter wheat genotypes
(Table 1) were selected based on the
level of resistance (field and
greenhouse) and their diverse
origins of resistance. A total of 64
genotypes (parents, F 1 , and
reciprocal F 1 ) were included in the
test. The study consisted of three
planting dates at three-day
intervals. In each planting, three to
five seeds of each experimental
unit were planted in plastic
conetainers filled with a peat-moss
and perlite mixture. Each planting
Table 1. Parental means, general combining ability (GCA), specific combining ability (SCA), and
reciprocal effects of septoria tritici blotch scores on the second leaf in an eight-parent diallel.
Resistant
Moderately
resistant Susceptible
Parent 1 2 3 4 5 6 7 8
1 KS94U338 —† 0.5 0.1 0.3 -1.9** 0.9** 0.6* -0.6*
2 Jagger 0.8* — -0.5 -1.0** -2.0** 1.0** 1.1** 2.0**
3 KS91W005-1-4 -0.9* -0.9* — -2.0* 1.6** 0.8** 1.0** 0.7*
4 KS91W0935-29-1 1.3** -0.6 0.0 — 1.3** 0.4 0.5 -0.6*
5 KS87822-2-1 0.3 0.1 -0.6 -0.5 — 0.1 0.3 0.5
6 SD93493 -0.1 -0.4 -0.2 0.1 0.2 — -0.8* -1.3**
7 Tandem -1.1* 0.3 0.2 -0.2 0.1 -0.2 — -0.9*
8 SD93500 -1.2** -0.3 -0.1 -1.1** -0.2 -0.2 -0.1 —
Parental means 1.4 1.4 1.9 5.8 5.8 8.0 8.3 8.7
Parental GCA -2.2** -1.6** -1.1** -0.5** 0.0 1.8** 1.6** 1.8**
*, ** Significantly different from zero at 0.05 and 0.01 probability levels, respectively.
† SCA effects are above the diagonal line, and reciprocal effects are below.