Research Highlights of the CIMMYT Wheat Program 1999-2000

Applying Physiological Strategies to Wheat Breeding
M.P. Reynolds, B. Skovmand, R.M. Trethowan,
R.P. Singh, and M. van Ginkel
Physiological Basis of Improved Yield and
Biomass Associated with the Lr19
Translocation from Agropyron elongatum
Although wheat yields have continued to improve
over the last 30 years (Calderini et al., 1999), the
physiological and genetic bases for this
improvement are only partially understood
(Reynolds et al., 1999). Nonetheless, yield increases
in several backgrounds have been shown to be
associated with introgression of a chromosome
segment containing Lr19, namely Agropyron
7DL.7Ag (Rajaram, Singh, and Montoya,
unpublished data). The introgression of Lr19 has
also been reported to be associated with increased
biomass (Singh et al., 1998).
As yield improvements due to increased
partitioning of biomass to grain yield reaches its
theoretical limit (Austin et al., 1980), breeding for
larger total biomass becomes increasingly
necessary if further genetic gains in yield potential
are to be realized. Higher biomass may be achieved
by: 1) increased interception of radiation by the
crop; 2) greater intrinsic radiation use efficiency
(RUE) throughout the crop cycle, and 3) improved
source-sink balance permitting higher sink demand
and, therefore, higher RUE during grainfilling.
Increased light interception could be achieved via
early ground cover or improved “stay-green” at the
end of the cycle. Improved RUE may be achieved,
for example, by decreasing photorespiration or
photoinhibtion (Loomis and Amthor, 1999), or
through improved canopy photosynthesis related
to factors such as canopy architecture. Better
source-sink balance may result from increased
partitioning of assimilates during spike
development so that grain number is increased;
this improves RUE during grainfilling as a
consequence of increased demand for assimilates.
Experiments were conducted to determine which of
these mechanisms were associated with greater
biomass in near-isogenic lines for the Lr19 gene
complex (Table 1) bred as described by Singh et al.
(1998) and grown under optimal conditions in
Ciudad Obregon, northwestern Mexico, for two
cycles between 1998-2000.
Results
Biomass, yield and yield components. Gene Lr19
was associated with increased yield, above-ground
biomass, and grain number in most backgrounds.
Averaged over both cycles, the main effect of Lr19
was a 10%, 8% , and 13% increase in yield, biomass,
and grain number, respectively, with the latter
coming mostly via increased numbers of grains per
Table 1. Biomass, yield and yield components for Lr19
isolines in spring wheat backgrounds, averaged over two
cycles, Ciudad Obregon, Sonora, Mexico, 1998-2000.
Biomass Yield No. grains Grains/ Kernel
(g/m 2 ) (g/m 2 ) (per m 2 ) spike wt (mg)
Main effect
Lr19 1,560 670 17,700 44.4 38.3
Control 1,440 610 15,600 39.9 39.4
P level 0.001 0.001 0.001 0.001 0.05
Background Lr19
Angostura + 1,575 630 15,500 37.9 40.9
Angostura - 1,435 585 13,000 36.0 44.9
Bacanora + 1,495 645 18,700 50.5 34.4
Bacanora - 1,525 620 17,500 43.0 35.6
Borlaug + 1,720 755 19,900 48.5 38.2
Borlaug - 1,520 630 17,300 37.9 36.5
Star + 1,630 690 18,500 43.9 37.2
Star - 1,590 640 17,400 39.7 37.0
Seri + 1,600 675 18,400 47.4 36.6
Seri - 1,420 630 16,000 45.3 39.6
Oasis + 1,350 655 15,300 38.4 42.6
Yecora - 1,180 545 12,700 37.5 42.9
P level (interaction) 0.05 0.05 ns ns 0.1
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