Agriculture Reference
In-Depth Information
need for local breeding programs with active participation from farmers
to achieve increased sustainability in low-input agricultural systems. The
idea being that local varieties or those most successfully produced in stress
environments will possess traits or adaptations that are advantageous to
crop growth, yield, and consumer expectations. Building on the idea of
natural selection, landraces, creole, and heirloom varieties [152], are best
suited to the environment in which they originated, having adapted ac-
cording to the selection pressures provided by the local agroecosystem.
Incorporation of valuable traits from heirlooms and landraces with high
yielding varieties can help optimize production in low-input systems, and
thus the potential of these systems to fulfi ll the food demand of the future.
At this point, it is important to briefl y distinguish breeding methods that
are used for autogamous (self-pollinating) species from those employed
for allogamous (outcrossing) crops. Autogamous crops (e.g., rice, wheat,
barley, oat, common bean, soybean, lentil, tomato) tolerate inbreeding,
thus allowing sexual propagation of highly homozygous varieties, mean-
ing that they can produce offspring that is genetically identical to the pa-
rental line when a high level of inbreeding is achieved. Thus, breeding
programs established for these crops rely on creating genetic combina-
tions by artifi cially crossing genotypes with traits of interest and undergo-
ing further rounds of selection and self-pollination to reach variety stabil-
ity, in which the new variety present the trait(s) of interest. Allogamous
species (e.g., maize, rye, pearl millet, cotton, sugar beet, canola, squash,
cucumber, papaya, cassava), however, show poorer genetic performance
under full homozygosity (i.e., inbred lines), while benefi ting of the het-
erozygous state via outcrossing. For these species, highly inbred parental
lines are usually selected and hybrid seeds are produced by combining
parental lines derived from distinct populations, in order to ensure hetero-
zygosity in fi rst generation (F
1
) seeds. The performance of F
2
populations
derived from hybrid seeds tends to lose agronomical performance in rela-
tion to its parental (F
1
) population, probably due to a higher degree of ho-
mozygosity. Thus, in commercial settings, the maintenance of high yields
of allogamous hybrid crops depends largely on the purchase of expensive
seeds year after year, encompassing a high-input supply.
Thus, breeding for autogamous species is more straightforward than
for allogamous crops regarding selection and maintenance of the genetic
