(go
to KOMUGI Home) (go
to WIS List) (go
to NO.76 Contents)
Long time breeding practice
has revealed that transgressive inheritance in scab resistance is of
frequent occurrence, but the so-called "resistance" is actually
varying degrees of tolerance to the extension of infection and not
infection itself. Owing to lack of source of resistance to infection
(note: recently Agropyron ciliare and A. repens were
found to be highly resistant to scab infection by Nanjing Agric.
Univ. and Sichuan Agric. Univ., independently) and a certain extent
of negative corelation between scab resistance and good agronomic
characters, it is difficult to achieve even a small breakthrough in
the improvement of scab resistance by the conventional method.
Therefore recurrent selection by using Taigu dominant male sterile
gene Ms2 or Ta1 has been adopted in recent years for
pyramiding the major and minor genes which control scab resistance.
Such a project was initiated and undertaken by Nanjing Agric. Univ.
and its partners. They crossed 15 selected scab resistant varieties
including landraces with five improved varieties carrying Ms2
gene to make a composite of 75 combinations. After three years of
intermating a CO population was established which was grown in four
locations under the same design. Phenotypic selection with an
intensity of 5-10% was practised aiming first at scab resistance and
paying considerable attention to major agronomic traits as well.
Seeds from the selected male sterile plants were bulked with equal
quantity to form the stock material for the next cycle. After three
cycles of phenotypic selection comparison among the four populations
from CO to C3 was made in Nanjing. The results showed that percent of
infected plants in the population and the number of infected
spikelets of infected plant reduded materially as the cycle advanced,
with an average of 20% decrease per cycle for the latter. After two
to three cycles of selection scab resistance of the population almost
approached the level of Sumai 3, and spike characters except kernel
weight were correspondingly improved with a gain per cycle varying
from 2-8% (Jiang et al, 1992). Meanwhile, South China Agric. Univ.
also conducted a similar study by crossing eight resistant parental
stocks with some high yielding varieties carrying Ms2 gene.
After several cycles of selection some promising lines designated as
T474, T229 and the like with acceptable scab resistance and desirable
agronomic characters were developed.
Breeding for semidwarfness
Early in 1957 Xianyang Prefectural Agric. Res. Inst. using Suwon
85 (bearing Rht1 and Rht2) as a source of dwarfhess
developed the first series of semidwarf intermediate materials among
which Xiannong 39 was a good representative. Then Northwest Agric.
Univ. by crossing Xiannong 39 again with a promising hybrid line
produced the first series of semidwarf varieties in which Aifeng 3
was the best one and released in 1971. Since then breeders from
Shandong, Sichuan, and Henan provinces had developed in succession a
number of semidwarfs which were widely grown in some major wheat
regions. Those varieties listed hereinbefore for the Yellow and Huai
Rivers valleys and Sichuan basin are all semidwarfs. Presently about
40% of the total wheat acreage is sown with semidwarfs.
In breeding for semidwarfness development of desirable intermediate
or link-up materials is very important. In addition to Xiannong 39,
there was another example. Shandong Agric. Univ. was successful in
developing an intermediate, link-up material called Aimengniu which
was a product of Aifeng 3//Mengxian 201/Neuzucht. It combined
dwarfness from Aifeng 3 and multiple disease resistance from
Neuzucht, but a little bit late in maturity. Subsequently breeders in
the University using this as a source of dwarfhess and disease
resistance in crossing bred a number of improved varieties known as
Lumai series which were widely grown in Shandong province. Another
experience in the breeding for semidwarfness is that selected crosses
between short or midstatured varieties may produce some semidwarfs
through transgressive segregation. For example, Huixian Red
(short)/Abbondanza (medium) -> Taishan 4 (semidwarf); Youbao
(short)/036 (tall, a Beijing selection) -> semidwarf transgressive
segregantsGand others.
<--Back |-->Next
(go
to KOMUGI Home) (go
to WIS List) (go
to NO.76 Contents)