79amounting to 40 kg/year, while the sowing area has only changed slightly over the
same period. Yield increases are always the joint result of developments in crop
production methods and the appearance of new cultivars. The two factors are inter-
dependent and the importance of each may vary from time to time and from place
to place, exhibiting a clear fl uctuation. After a time the old cultivars are unable to
exploit further changes in production conditions, especially an increase in the inten-
sity of crop production, so they become an obstacle to development. By developing
new types of cultivars, a further increase in production can be achieved and other
factors, such as nutrient replacement, plant protection and other agronomic mea-
sures become vital for the full exploitation of the yield potential of the new culti-
vars. If agricultural production is to be really effi cient, there must be a harmonious
balance between the two factors, cultivar and technology.
The development of new cultivars adapted to new management practices or
growing conditions has in turn allowed management practices to be further
improved, within the limits set by the given environmental conditions. The three
decades starting in 1960 were a period of intensive mechanisation and of rapid
developments in the production technology. The rate of mineral fertiliser applied
per hectare rose from 50 kg/ha to over 200 kg/ha ( FAOSTAT ), and there was a simi-
lar increase in the application of fungicides and insecticides.
The increasing use of fertilisers and the greater level of mechanisation required
the cultivation of new plant varieties that could be harvested without lodging and
which responded to larger quantities of inputs with higher yields. The new wheat
cultivars developed by breeders to suit the climatic conditions in specifi c ecological
regions had greater productivity than the cultivars previously sown, with stable
yields and grain quality meeting the requirements of processors and consumers. The
potential area on which a particular cultivar can be grown is relatively restricted in
the case of winter cereal species, but considerably wider for spring types. Due to the
cultivar × environment interaction, regional breeding centres or regional experimental
networks were established, which continually supply growers with new cultivars.
Increasing or even simply maintaining the yield level requires the regular intro-
duction of new cultivars. Farmers are constantly seeking cultivars with greater yield
potential, because the increasing costs of land, input materials and labour mean that
crop production will only remain profi table if yield averages continually increase.
Maintaining food safety acts in the same direction, as a 60 % increase in wheat
production will be needed by 2050 to meet the demands of a growing population
with a changing diet.
Though it varied in each period and region, the annual genetic gain for grain
yield in developed countries typically ranged from 0.5 to 1 %/year in the second
half of the last century (Peltonen-Sainio and Peltonen 1994 ; Khalil et al. 1995 ).
Genetic gain is responsible for approximately half the yield increment (Kuhr et al.
1985 ; MacKey 1993 ), while the other half can be attributed to developments in the
technology. A retardation in the rate of genetic gain has been observed in several
regions in recent years.
A regular change of cultivar is essential to counteract the appearance of new,
virulent fungal races. According to a survey carried out in 26 countries, resistance
3 Wheat Breeding: Current Status and Bottlenecks