Principles of Plant Genetics and Breeding

504 CHAPTER 29
Figure 3 Rice cultivars are evaluated for their reaction to a
mixture of several races of Pyricularia grisea in disease
screening nurseries.
Results from the URRN are analyzed during the
winter and demonstrate that RU9603178 has very
good main and ratoon crop yield, good resistance to
all races of blast disease (including an IB49 rating of 1
on a scale of 0 to 9), good tolerance to sheath blight
(rating of 4 on a scale of 0 to 9) and straighthead, very
clear, non-chalky grain, a cooking quality of typical
US long grains, and excellent milling quality. It is
advanced for testing in 1997 along with one of the
other four entries (BPRE 18) that had been tested in the
Texas statewide trials.
1997
Ten F 9 -derived F 10 panicle rows of RU9603178 and of
BPRE 18 are planted in the summer nursery and 20
panicles are selected from one row of the two entries.
Bulked F 10 seed from the 1996 URRN yield trial in
Beaumont of entry RU9603178 is used to be planted
in the advanced section of the 1997 URRN as entry 23.
The other B8910 project line (BPRE 18) is entered into
the advanced URRN as entry 32 using seed harvested
from one of the 1996 Texas replicated trials. The
advanced entries of the URRN are tested using four
replications at the four state locations and the Texas
entries of the URRN are also evaluated in the multilocation
replicated trials within Texas.
Results from these trials indicate that RU9603178
continues to demonstrate competitive yield potential,
excellent milling quality, and has moderate tolerance
(rating of 6) to the sheath blight pathogen. The other
B8910 line, entry 32, does not perform as well as
RU9603178 and is dropped from further testing.
Moreover, RU9603178 demonstrates resistance to all
races of the blast fungus. Based upon this spectrum of
resistance and the pedigree of RU960178, this suggests
that the line may possess a novel major resistance
gene to P. grisea. Previous research had demonstrated
success in developing genetic markers associated with
major genes that control rice cooking quality (Ayres
et al. 1997). This spawned further research to identify
the novel resistance gene and develop closely linked
DNA markers.
During the fall of 1997, 20 F 11 panicles from the
summer breeding nursery selection of RU9603178 are
planted in the Puerto Rico nursery; 287 F 12 panicles
are harvested from the 20 panicle rows in Puerto Rico.
Figure 4 Milled rice flour is used to determine grain amylose
1998
content.
The 287 F12 panicles are planted in an isolation block
during the summer at Beaumont (Headrow 1). Thirty
rows are selected and 20 panicles per row are harvested. Twenty-two rows are removed that are earlier, later, or taller than the
others and then the remaining rows are bulk harvested. In addition, detailed phenotypic data is collected from the Headrow 1
field as an objective description of the cultivar, which is required for application to the state department of agriculture certified
seed program.
RU9603178 is evaluated in the 1998 URRN and Texas statewide trials using the bulked harvested F11 seed from the 1997 yield
trial. Results demonstrate that RU9603178 has main crop and ratoon crop yields competitive with other cultivars in its maturity
group, some lodging susceptibility at two locations, excellent milling yield, and good tolerance to sheath blight disease (rating