Biology Reference
In-Depth Information
mapped in a 29.6-Kb interval, in which three can-
didate genes for Mi nematode resistance were
identified and further investigated (Xu et al.
2013).
Work at the University of Missouri indi-
cated resistance among exotic accessions to mul-
tiple nematode species, which include SCN,
RKN, and RN, in the USDA germplasm col-
lection will be valuable sources for develop-
ing resistance to important nematode species
in soybean. The development and accessibility
of molecular marker technologies enabled soy-
bean researchers to accurately localize genomic
regions and their associated DNA markers,
which can be effectively employed in molec-
ular breeding. Moreover, the WGS technology
provided a powerful genomics tool to narrow
genomic locations based on an ultra-high-density
bin map (Huang et al. 2009; Xie et al. 2010)
and to pinpoint candidate genes underlying resis-
tance to nematode species, leading to study of
gene cloning and functionality.
expands to encompass 100 to 200 cells through
extensive cell wall dissolution and cytoplasmic
fusion (Rebois et al. 1975). After fertilization
by an adult male, a mature vermiform female,
while feeding on a stellar syncytium, produces
30 to 200 eggs in a gelatinous matrix, which
surrounds the swollen posterior portion of the
female body producing from the root surface in
a kidney-like shape (Robinson 2002).
It was observed that many cellular char-
acteristics of reniform nematode-induced syn-
cytium were similar to those formed by cyst
nematodes, such as increased metabolic activ-
ity, hypertrophied nuclei, and granular, densely
staining cytoplasm (Agudelo et al. 2005; Rebois
et al. 1975; Vovlas and Lamberti 1990). Fur-
thermore, in order to penetrate the epidermis
and move through the root, RN uses mechani-
cal force coupled with the activity of cell wall-
degrading enzymes secreted by the esophageal
gland cells (Baum et al. 2007). Among these
enzymes, glycosyl hydrolase family 5 (GHF5)
beta-1,4-endoglucanases, also known as cellu-
lases, are well represented and have been isolated
from many plant-parasites (Baum et al. 2007).
Subsequently, this enzyme was further investi-
gated and characterized when analyzing a cDNA
library constructed from J2 juvenile females of
RN (Wubben et al. 2010a, 2010b).
Reniform Nematode
LifeCycleandParasiticBiology
Similar to other plant-parasitic nematodes, the
RN's life cycle begins in the soil, with the
J1 molt to the J2 stage occurring in the egg.
The J2 juvenile hatches from the egg. How-
ever, unlike most endoparasitic nematodes, the
RN J2 juvenile does not immediately infect
the roots. Instead, it becomes inactive and pro-
gresses through three superimposed molts with-
out feeding. The crescent-shaped and inactive J3
and J4 juveniles show slight movements in the
head and tail regions, but the stylet, metacarpus,
and valve are still not present (Gaur and Perry
1991). The final molt then produces approxi-
mately equal numbers of adult males or imma-
ture vermiform females (Robinson et al. 1997).
While nonparasitic males do not feed, parasitic
vermiform females penetrate the epidermis and
cortical parenchyma of the root and establish a
feeding site (syncytium). The syncytium quickly
GeneticVariationforVirulence
Unlike other parasitic nematode species classi-
fied into different races based on their virulence
levels in differentials of host plants, RN nema-
todes used in studies of crop plants so far were
typically derived from inbred RN populations,
which were locally maintained on host plants in
a greenhouse. For instance, Davis et al. (1996)
used a culture of field RN nematode population in
North Carolina to evaluate soybean germplasm
for resistance to this parasite. Similarly, Robbins
et al. (2000, 2001, 2002) screened large num-
bers of both private and public soybean cultivars
and lines for resistance to RN using inoculum
from the same inbred RN populations, which
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