Contents - Faperta

Physico-Chemical and Molecular Markers for Resistance to Insect Pests 179
are also underway to evaluate interspecifi c mapping populations based on the crosses ICC
3137 (C. arietinum) IG 72933 (C. reticulatum) and ICC 3137 IG 72953 (C. reticulatum) for
resistance to pod borer to identify QTLs linked to various components of resistance to
H. armigera (Sharma, Gaur, and Hoisington, 2005).
Pigeonpea
A few studies have been conducted to investigate polymorphism in pigeonpea and its wild
relatives (Sharma and Crouch, 2004; Sharma, Gaur, and Hoisingtom, 2005). Screening of
ten allozymes across one Zambian and 20 Indian genotypes of cultivated pigeonpea
detected limited polymorphism (Boehringer, Lebot, and Aradhya, 1991), while Nadimpalli
et al. (1993) used nuclear RFLPs to determine phylogenetic relationships among 12 species
in four genera (Cajanus, Dunbaria, Eriosema, and Rhynchosia). Fifteen random genomic
probes and six restriction enzymes revealed limited variation within each species, while
considerable polymorphism was observed between the species. Cajanus cajan (L.) Millsp.
was found to be closer to C. scarabaeoides than to C. cajanifolius (Haines). Ratnaparkhe et al.
(1995) studied RAPD polymorphism in cultivated pigeonpea and its 13 wild relatives. The
level of polymorphism among the wild species was very high, while little polymorphism
was detected within the cultivated species. Low levels of genetic diversity were also
observed in the cultivated pigeonpea using DArTs (Yang et al., 2006). Only 64 markers
were polymorphic among the cultivated pigeonpeas. DArT markers also revealed genetic
relationships among the accessions of different species consistent with the available information
and systematic classifi cation.
Variations in length and restriction sites of ribosomal DNA have also been studied
among eight Cajanus species (Parani et al., 2000). The six genotypes of C. cajan did not show
polymorphism in any of the enzyme-probe combinations, whereas RFLPs were readily
detected among the eight species in all enzyme-probe combinations. The cultigen was
found to be closely related to C. scarabaeoides. The studies indicated that isozyme, RAPD,
and RFLP markers may not be adequate to develop a genomic map of pigeonpea based on
intraspecifi c mapping populations. However, recently developed microsatellite markers
have detected polymorphism in diverse pigeonpea germplasm using manual slab gel systems
(Burns et al., 2001). Six of these markers have detected extensive diversity within and
between cultivated pigeonpea accessions using capillary electrophoresis. Thus, it appears
that SSR markers will readily detect polymorphism in breeding populations, although the
number currently available is a limitation to their application. For this reason, a major SSR
marker development program has been initiated in pigeonpea. Panguluri et al. (2006) used
AFLP markers to detect polymorphism in cultivated pigeonpea and two of its wild relatives
Cajanus volubilis Lour. and Rhynchosia bracteata Benth. ex Bak. The two wild species
shared only 7.15% of the bands with the pigeonpea, whereas 86.71% common bands were
observed among the pigeonpea cultivars. Similarly, 62.08% bands were polymorphic
between C. volubilis and pigeonpea in comparison to 63.33% of polymorphic bands
between R. bracteata and pigeonpea, and 13.28% polymorphic bands among pigeonpea
cultivars. High levels of resistance to pod borer, H. armigera, and pod fl y, Melanagromyza
obtusa (Malloch), have been identifi ed in wild relatives of pigeonpea such as C. scarabaeoides,
C. sericeus van der Maesen, and C. acutifolius (Sharma et al., 2001, 2003b), which can
be easily crossed with the cultivated pigeonpea. A mapping population based on C. cajan
C. scarabaeoides is under development, and will be evaluated for resistance to H. armigera to
identify QTLs linked for resistance to these insects (Sharma and Crouch, 2004).