The future course of domestication will continue to rely on
changes to the architecture, metabolism and physiology of crops.
To reach new levels of crop yield and new uses for crops, a
combination of applied and also theoretical approaches involving
computer or systems' biology models will be required. To cope
with new challenges to crop production, efficient approaches
to screen germplasm for genes to both biotic and abiotic stresses
in wild and cultivated germplasm are needed. Crops primarily
used for food are now also being used to meet demands for sustainable
fuel supply, while the use of plants for construction timbers
and fibres in paper, textiles and composite products continues
to increase. To provide value-added crops, new products from
crops are being developed. Specialized plant products for processing
(such as starches, oils, even plastics) for food, pharmaceutical,
cosmetic and industrial uses are required for growing markets
(
Heslop-Harrison, 2002).
As information accumulates on domestication-related traits andtheir genome distribution, new avenues to attain higher yieldand to tailor-make crops are opened up. Analysis of yield andplant height in a cross between two Japanese rice varieties,‘Koshihikari’ and ‘Habataki’, revealedseveral QTLs for each trait. One QTL, Gn1a, increased grainproductivity and acts by altering the production of the enzymecytokinin oxidase/dehydrogenase that degrades the phytohormonecytokinin. By reducing the expression of Gn1a, cytokinin accumulatesin inflorescence meristems, resulting in an increased numberof grains and, hence, a plant with the potential for increasedyield (Ashikari et al., 2005). By accumulating a variety ofyield-related QTLs for increasing both source to produce photosynthateand sink to accept photosynthate, new levels of yield may beachieved.
Throughout history, plants have been subjected to changing climate,and farmers have adopted new species and varieties to meet thechallenges; indeed, post-glacial climate changes may have beenone of the factors leading to the origin of agriculture andplant domestication. Climate change is affecting agriculturein the 21st century; some changes will be met within existingadaptations of plants, but other factors such as increased UVand carbon dioxide levels require new selections based on understandingof plant responses. Hidema and Kumagai (2006) reported considerablevariation in UVB sensitivity of rice cultivars, which was causedby differences of one or two bases in the CPD (cyclobutane pyrimidinedimer) photolyase, altering the activity of the enzyme. Theysuggest that the resistance of rice to UVB radiation can thereforebe increased by selective breeding or bioengineering of thegenes encoding CPD photolyase. Although carbon dioxide enhancementis regularly used to improve glasshouse production, it is notclear how field crops will respond to changes in atmosphericcarbon dioxide concentrations, involving complex interactionsof phytosythesis with light and dark respiration (Bunce, 2005).
There is no naturally occurring waxy wheat variety but in bread
wheat there are waxy loci in each of its three different genomes,
A, B and D. The waxy locus encodes starch granule protein 1
(SGP-1). Different isoforms are encoded by genes in each genome
(
sgpA1,
sgpB1 and
sgpD1). In the germplasm collection of bread
wheat, cultivars lacking one of the three isoforms were found,
two cultivars from Korea lacked SGP-A1, one from Japan lacked
SPG-B1 and one from Turkey lacked SPG-D1. By making appropriate
crosses, these genes were combined in a single plant, resulting
in the first waxy wheat, which had a null for all three isoforms
of SGP-1 (
Yamamori et al., 2000), an example of using markers
for identification of alleles and then marker-assisted selection
to find the desired allele combination. The effort to produce
waxy wheat in Japan has led to its use as an ingredient for
improved Japanese-style noodles. These examples show the value
of screening germplasm collections with diverse material for
useful genetic variation, but also emphasize that it is not
always necessary to search in exotic material or employ radical
techniques to make innovative progress in plant breeding.
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