Contents - Faperta

Mechanisms and Inheritance of Resistance to Insect Pests 131
Escape
Avoidance of insect damage through early or late fl owering during periods of low insect
abundance is another mechanism of resistance, called pseudo-resistance (Kogan, 1982;
Smith, 2005). It is not a true mechanism of resistance, but serves as an effective means of
avoiding pest damage. Many of the landrace cultivars have evolved such that they fl ower
during the periods of low insect activity. This mechanism can be exploited to minimize
insect damage, depending on the length of the cropping season, and the cultivars grown.
Breeding for Resistance to Insect Pests
Several methods have been used to transfer insect resistance genes into high-yielding cultivars
(Panda and Khush, 1995; Smith 2005). Mass selection, pure line selection, recurrent
selection, and backcross methods have been used to incorporate insect resistance genes
into the crop plants. In self-pollinated crops, backcross, bulk, and pedigree breeding have
been used to incorporate resistance genes into agronomically desirable cultivars, while
mass selection and recurrent selection methods have been used in cross pollinated crops.
Mass Selection
Mass selection involves selecting individual insect-resistant plants in a population in each
generation (cycle of selection), combining the seed of the resistant plants, and growing
progenies in the following generation. It allows selection of several insect-resistant plants
in each cycle of selection. Maximum improvement for resistance is achieved during initial
selection, followed by two to fi ve additional cycles of selection. Mass selection has been
used effectively to breed for resistance to the potato leafhopper, Empoasca fabae (Harris)
(Sanford and Ladd, 1983) and to identify genotypes with resistance to sugarbeet root maggot,
Tetanops myopaeformis Roder (Theurer et al., 1982). Pure line selection is another form of
mass selection that involves the selection of individual resistant plants that are advanced
separately. In each cycle of selection, resistant selections are selfed and advanced. In crosspollinated
crops, individual selections are interplanted in a later selection cycle to form a
composite of all the insect-resistant plants/lines.
Recurrent Selection
Recurrent selection has been used to concentrate insect resistance genes from diverse
sources into the same background through several cycles of intermating and selection. In
each cycle, resistant plants are selected among the progeny produced through a previous
mating of resistant individuals. Recurrent selection allows introduction of resistance to
several insects and diseases from different sources in later selection cycles. Recurrent selection
has been used to increase the levels of resistance in maize to European corn borer
O. nubilalis (Russell, Lawrence, and Guthrie, 1979; Klenke, Russell, and Guthrie, 1986). The
corn borer damage decreased signifi cantly after four cycles of selection. Variability for
resistance to O. nubilalis also decreased in each cycle of selection. Recurrent selection has
also been used to increase the level of resistance in maize populations to corn earworm,
H. zea, and fall armyworm, Spodoptera frugiperda ( J.E. Smith) (Widstrom, 1989; Widstrom et al.,