(go
to KOMUGI Home) (go
to WIS List) (go
to NO.76 Contents)
Hybrid wheat
Presently 12 units are included in the national network in which
(T. timopheevi) cytoplasmic male steriles (T-type) are
emphasized although (Ae. kotschyi) cytoplasm (K-type), (Ae.
ventricosa) cytoplasm (V-type) and others including CHA are also
extensively studied. In the past five years considerable progress has
been made: (1) General level of various characters of T-type A
and B lines has been improved. Jiangsu AAS has successfully developed
the first series of semidwarfs through the introduction of Rht3
gene to ordinary T-type A lines and produced some hybrid wheats
such as Ningai/R14 that combined semidwarfness, disease resistance
and preharvest sprouting resistance with high yield potential pretty
well. (2) Yielding capacity of some T-type R lines is greatly
improved, for example, Ke 82-Hui 2 (Helongjiang), T 808/Zheng
65//#6609 (Henan), Yuan 8501 (Beijing), etc. approached or
equalled the commercial varieties in yield. (3) A few set of Ktype
and V-type A, B, and R lines were developed in 1988 and hybrid
wheats, derived from them are now under yield trials. K-type and
V-type male sterile lines have several advantages over T-type ones in
that the former have more sources of fertility restorers (although
the degree of fertility restoration has to be improved) than the
latter and most present day cultivars bearing 1BL/1RS translocation
are their maintainers. Unfortunately, most K-type A lines with
1BL/1RS translocation usually produce haploid plants or twin
seedlings, because there is a Pty gene located on chomosome
arm 1RS which tends to induce parthenogenesis. This can be overcome
though screening. It is estimated that a frequency of haploids less
than 5% will not influence hybrid seed production and yield
performance of hybrid wheats. In addition to Ae. kotschyi and
Ae. ventricosa cytoplasms, a few people are engaged in
the development of hybrid wheats with sterile cytoplasms from
T. aestivum, Ae. squarrosa and other alien species. (4)
CHA is a prospective alternative for the utilization of heterosis. WL
84811 and Sc2503 have been proven to be excellent CHAs in use. Hebei
Normal University and its partners were successful in using a local
CHA in combination with physical means to produce hybrid seeds for a
small-scaled hybrid wheat production in Hebei Province attaining a
yield increase of 20% over the standard variety. Hybrid wheat
combinations produced by CHA such as Ningai 13 x E-mai 9 from Jiangsu
AAS and #1008 x Shaan 7859 from Shaanxi AAS and some others outyield
the standard variety by more than 10-15%. Furthermore, a few
agricultural universities have synthesized some CHAs such as BAU1,
BAU2 and XN8614 in the laboratory whose effectiveness is
nearly equal to WL 84811. If they could be produced in a large scale
hybrid wheats for commercial use will be greatly enhanced.
Finally, it is interesting to note that three institutes have
independently found from off-seasoned growing of their breeding
materials some photo-thermo-sensitive male sterile wheats which are
male sterile under short day and low temperature conditions (at the
reduction divisions of PMCs or early booting stage) but fertile under
long day and warm temperature environments. They have now developed
some agronomically desirable "dual lines" which can be used as either
A line or B line by differential planting in time, and have also
identified some hybrid combinations which showed strong heterosis in
yield trials. For example, Hunan Agriculatural College developed
three photo-thermo-sensitive male sterile lines designated as ES-3,
ES-4 and ES-5 from a common wheat with alien pedigree which were male
sterile under normal autumn planting at Changsa and fertile under
summer planting at Kuming or late autumn planting at Changsa. The
critical daylength and temperture for fertility transformation at
Changsa are approximately 12 hr and 10oC, respectively.
These photo-and thermo-sensitive male sterile lines have 100% sterile
plants with 98-100% sterile florets as counted from the outer two
florets of the spikelet (Ho et al 1992, unpublished). Scientists from
Chongqing Crop Institute, Sichuan Province and Southwest Agric. Univ.
also developed some similar "dual lines" either from the common wheat
or from a derivative of K-type cytoplasmic male sterile line with
slightly different responses to temperature (Tan et al 1992,
unpublished, Fu and Ruan 1992). The mode of inheritance of this
character and more exact responses to different regimes of daylength
and temperature in different regions are now under study. If "dual
lines" work well under a range of environments then the way to hybrid
wheat production will be much broadened.
<--Back |-->Next
(go
to KOMUGI Home) (go
to WIS List) (go
to NO.76 Contents)