Maize - Bioenergy Crop Plants - page 422

function of soil nutrient content, moisture level, and soil temperature, which affects nutrient
availability in an unpredictable manner. Unpredictable abiotic stresses around flowering are known
to most severely affect grain yield.
The picture that emerges from the aforementioned discussion is that in the light of the
unpredictable components of the environmental variation, which make it extremely difficult to
discern the effects of a single or a few genetic or transgenic factors on increasing grain yield,
testing varieties over multiple years and geographic locations is required. Of course, it is easier
to determine the effect of a single gene or a few genes on drastically reducing grain yield (for
example, through an increase in barrenness, lodging, or a severe reduction in plant height). What
is challenging is to measure the effect of a single or a few genes on increasing grain yield. A
diagrammatic representation of genetic and environmental factors influencing plant growth and
development is shown in Figures 16.12 and 16.13.

16.8 BIotechnoloGIcal oPPortunItIes,
outcomes, and Future ProsPects
Rapid advances in genomic sciences have provided an abundance of molecular tools that can
potentially be used to alter plant structure and function. Despite considerable progress in the area
of cell wall synthesis over the last decade, some of the problems remain unsolved. For example,
molecular components of GAX formation as well as its acetylation remain to be identified. A
discussion on prospects and attempts to alter plant biomass and composition follows. Recent reviews
cover other complementary aspects of transgenic manipulation to improve maize for ethanol
production (Torney et al. 2007; Gressel 2008).

ti

v

i

G g

E g

G v

E v

G r

E r

FIGure 16.12 (see color insert) Illustration of complex genotype × environment effects on plant growth.
G, genotype; E, environment; subscripts g , germination; v , vegetative growth; and r , reproductive growth. Dark-
to-light gradient is indicative of genotypic effects (dark), genotype × environment effects (transition from dark
to light), and environmental effects (light, at the edge of each developmental stage). Environmental factors that
affect germination are different from the ones that affect vegetative growth, which are different from the ones
that the plant experiences during reproductive growth. Environment can vary independently during each of
these phases, increasing the unpredictability of plant performance. For further details, see Figure 16.13.