Biology Reference
In-Depth Information
compared to nematicide application and rotation
of non-host crops. The evaluations of soybean
germplasm and varieties for resistance to RN
identified many sources of resistance, such as
PI 437654 (Davis et al. 1996), cultivars Picket
and Dyer (Rebois et al. 1968), and Forrest and
Hartwig (Davis et al. 1996; Robbins et al. 1994).
A previous genetic study in soybean showed
that resistance to RN was controlled by a reces-
sive allele (Williams et al. 1981). However, in
another study, Harville et al. (1985) reported that
two loci, designated Rn1 and Rn2 , were associ-
ated with RN resistance with unequal effects.
Similar to the studies of SCN and RKN, the
advent of genetic marker technologies facili-
tated the identification and molecular character-
ization of QTL or genes for RN resistance. So
far, several QTL for RN resistance and associated
molecular markers were identified and mapped
to chromosomes 11, 18, and 19 (LGs B1, G,
and L, respectively) (Ha et al. 2007; Webb et al.
1995). Genetic mapping and host plant resis-
tance genes is reviewed in more detail later in
this chapter.
Nematode Biology and Host
Response to Nematodes
Soybean Cyst Nematode
LifeCycleandParasiticBiology
H. glycines nematode is a migratory and obli-
gate sedentary endoparasitic pathogen. In the
soil, its life cycle starts when a developed first-
stage juvenile (J1) forms in a viable egg. An
infective second-stage juvenile (J2) then emerges
from the egg (Figure 7.1). The J2 nematode
locates host plant roots by its attraction to dif-
fusates. It then mechanically penetrates the root
cell wall using its protrusible stylet, while secret-
ing cell wall-hydrolyzing enzymes to facili-
tate migration toward the root vasculature. Once
reaching the vasculature of the roots, the nema-
tode selects an individual cell to initiate the
Fig. 7.1. A life cycle of Heterodera glycines nematode. Typically, a first-stage juvenile (J1) forms in an
egg released from a cyst. A second-stage juvenile (J2) then hatches and emerges from the egg. Third- and
fourth-stage juveniles (J3 and J4) develop in the roots of the host plant. An adult male fertilizes an adult
female, which produces eggs externally. A dead body of a female serves as a cyst containing eggs (adapted
from University of Minnesota Extension Publication “The Soybean Cyst Nematode” by S. Chen, et al.). For
a color version of this figure, please refer to the color plate.
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