Fundamental Biochemical and Biotechnological Principles of Biomass Growth and Use 17
compete with food production. However, handling the large volume of water related
with algae cultivation (pumping, product isolation) is costly and a significant hurdle in
commercialization.
1.3.7 Plant Breeding
Plant performance characteristics and plant compounds are subject to optimization
by plant breeding. If features like fruit and biomass yield (ton ha−^1 year−^1 ) or seed
and biomass composition (e.g., starch, lipid, or lignin content) are targeted, genes in
so-called output traits are addressed. These are the metabolic pathways controlling
growth, biomass composition, and yield. Other breeding programs aim on cultivation
parameters like germination rate and resistance against microbial pathogens and insects
or draught. These approaches aim on genetic input traits. In any case, plant genes are
modified either bycombination breeding,smart breeding,orgenetic engineering.
Combination breedingis the most commonly used breeding method today. Two
parent plants are crossed, and by natural recombination the genomes of both parent
plants are rearranged and redistributed according to the laws of heredity (first realized
by Gregor Mendel (1822–1884); Austria). Subsequent filial generations are cultivated
in green houses and analyzed for the quality of the targeted traits. After selecting
improved varieties, the breeding process is repeated. As breeders need to cultivate each
generation and analyze the targeted characteristic by checking the whole plant, this
method is extremely time consuming. It may take 10 years plus 2–4 years for official
registration and seed propagation before entering the market.
In addition to this traditional method, plant breeders increasingly use the tools of
molecular genetics. The plant genome is sequenced, and molecular markers tagging the
desired quality are introduced bysmart breeding. The result of genetic recombination
becomes much more predictable and by analyzing the genetic markers in the laboratory
the desired genetic combination can be identified on cellular level within short time.
Plant genome recombination and subsequent selection therefore can be performed
much more efficiently.
Genetic engineeringalso uses selected genome sequences but is able to take advantage
of nature’s genetic diversity by introducing beneficial genes from other species (plants,
bacteria) into the plant genome. In contrast tosmart breeding, the resulting varieties
are classified as genetically modified (GM). Critics point out that foreign genes in a
plant may unfold unexpected effects or cross into wild species in an uncontrollable
way. Therefore, release of GM plants is strictly regulated. GM corn, soybean, rapeseed,
and cotton are cultivated in South and North America, China, and Southeast Asia but
Europe acts more restrictive (Tables 1.20 and 1.21).
1.3.8 Basic Transformation Principles
Vegetable biomass and its compounds are subject to various industrial transformation
as described here. Depending on the pretreatment of the raw materials, a distinction is
drawn between first-, second-, and third-generation processes and product.
1.3.8.1 First Generation
Microorganisms of industrial relevance like Escherichia coli, Corynebacterium
glutamicum,orSaccharomyces saccharomyceseasily take up and metabolize sucrose
