Broadening the Genetic Base and Introgression of MYMV Resistance and Yield Improvement through Unexplored Genes from Wild Relatives in Mungbean

Abstract

Introgression of unexplored genes from the wild relatives could be rewarding for broadening the genetic base of important traits such as yield, yield attributes and resistance to biotic and abiotic stresses in pulses. Aimed at developing superior segre- gants for yield coupled with yellow mosaic virus resistance (MYMV), interspecific direct crosses were attempted in Vigna radiata var. VRM (Gg) 1 with two accessions of Vigna umbel- lata ( yellow and red). Even though crossability barriers were predominant, it was possible to recover interspecific hybrids in direct crosses. F 1 plants of V. radiata x V. umbellata were found to be intermediate in phenotype with light green colour leaves. The reproductive parts tend to resemble V. umbellate , with double peduncle in one leaf axis. No pod set was observed when F 1s were selfed nor in their corresponding backcrosses with the parents. The F 1 plants produced more than 4000 flow- ers per plant, but spontaneous sterility was observed both in female and male parts of the flowers. Detailed cytological stud- ies were carried out for male and female sterility. Male sterility was due to meiotic irregularities viz., unequal separation of tetrads and female sterility was due to degeneration of mega- spore during megasporogenesis. Hence, irradiation techniques were applied to recover fertile plants in F 1 hybrids. The paren- tal seeds were irradiated with 100, 200, 300, 400 and 500 Gy doses. The pod set percentage was increased due to irradiation. In normal crosses, pod set ranged from 2.00% (VBN (Gg) 2 × Vigna umbellata red) to 4.40% (VRM (Gg) 1 × V. umbellata red). In crosses resulted from irradiated parents, pod set ranged from 2.70% (CO 6 × V. umbellata yellow) to 4.90% (VRM (Gg) 1 × Vigna umbellata yellow) among crosses involving parents treated with 100Gy. Fertile F 1 hybrid plants were ob- tained from a cross between Vigna radiata var. VRM (Gg) 1 and V. umbellata red ( both parents treated with 200 Gy). The fertile F 1 phenotype was generally towards the female parent, but traits like orientation of top leaves, tendrilness and number of seeds per pod shifted towards the male parent.

Full text

Plant Mutation Reports, Vol. 2, No. 1, December 2008
33
Research Article
Broadening the Genetic Base and Introgression of MYMV Resistance and Yield Improvement through
Unexplored Genes from Wild Relatives in Mungbean
M. Pandiyan
1*
, N. Ramamoorthi
1
, S.K. Ganesh
1
, S. Jebaraj
3
, P. Pagarajan
2
and P. Balasubramanian
2
1
National Pulses Research Centre (TNAU), Vamban – 622 303, TN, India
2
Centre for Plant Molecular Biology, TNAU, Coimbatore – 641 003, TN, India
3
Tamil Nadu Rice Research Institute, Aduthurai – 612 303, TN, India
*
E-mail: mpandiyan8@yahoo.co.in
Abstract
Introgression of unexplored genes from the wild relatives could
be rewarding for broadening the genetic base of important
traits such as yield, yield attributes and resistance to biotic and
abiotic stresses in pulses. Aimed at developing superior segre-
gants for yield coupled with yellow mosaic virus resistance
(MYMV), interspecific direct crosses were attempted in Vigna
radiata var. VRM (Gg) 1 with two accessions of Vigna umbel-
lata (yellow and red). Even though crossability barriers were
predominant, it was possible to recover interspecific hybrids in
direct crosses. F
1
plants of V. radiata x V. umbellata were
found to be intermediate in phenotype with light green colour
leaves. The reproductive parts tend to resemble V. umbellate,
with double peduncle in one leaf axis. No pod set was observed
when F
1
s were selfed nor in their corresponding backcrosses
with the parents. The F
1
plants produced more than 4000 flow-
ers per plant, but spontaneous sterility was observed both in
female and male parts of the flowers. Detailed cytological stud-
ies were carried out for male and female sterility. Male sterility
was due to meiotic irregularities viz., unequal separation of
tetrads and female sterility was due to degeneration of mega-
spore during megasporogenesis. Hence, irradiation techniques
were applied to recover fertile plants in F
1
hybrids. The paren-
tal seeds were irradiated with 100, 200, 300, 400 and 500 Gy
doses. The pod set percentage was increased due to irradiation.
In normal crosses, pod set ranged from 2.00% (VBN (Gg) 2 ×
Vigna umbellata red) to 4.40% (VRM (Gg) 1 × V. umbellata
red). In crosses resulted from irradiated parents, pod set ranged
from 2.70% (CO 6 × V. umbellata yellow) to 4.90% (VRM
(Gg) 1 × Vigna umbellata yellow) among crosses involving
parents treated with 100Gy. Fertile F
1
hybrid plants were ob-
tained from a cross between Vigna radiata var. VRM (Gg) 1
and V. umbellata red (both parents treated with 200 Gy). The
fertile F
1
phenotype was generally towards the female parent,
but traits like orientation of top leaves, tendrilness and number
of seeds per pod shifted towards the male parent.
Introduction
Vigna radiata (L.) Wilczek, commonly known as green-
gram or mungbean is the most widely distributed species
among the six Asiatic wild Vigna accessions. The culti-
vated species V. radiata has desirable characters like
short cycle duration, high yield, amenability for crop ro-
tation and undesirable characters like susceptibility to
bruchids and yellow mosaic virus, the latter provoking
100% yield loss on severely affected plants. There is
therefore a need to improve the greengram by hybridisa-
tion with wild species (Boling et al., 1961). Among the
wild Vigna species studied, V. umbellata (rice bean) has
high test weight and resistance to bruchids and yellow
mosaic virus. However, the recovered F
1
is both male and
female sterile, and to overcome this problem and recover
fertile F
1
s mutation studies were undertaken. The mate-
rial generated through mutagenesis can also contribute as
a reservoir of novel genes for an improvement of yield
and yield components. Thus, this study was taken up to
attempt coupling mutation and interspecific hybridization
of V. radiata with species in secondary pools to generate
variability for better yield and resistant to yellow mosaic
virus, and to compare such variability created among the
segregants generated.
Materials and methods
Two Vigna species, V. radiata (mungbean) and V. umbel-
lata (rice bean) were used. Normal, i.e. non irradiated,
and irradiated crosses of six accessions of V. radiata
(VBN1, VBN(Gg)2, KM2, K1, VRM(Gg)1 and CO 6) as
female parents and two accessions of V. umbellata (red
[Vur] and yellow [Vuy]), both as male parents, were pro-
grammed. Parental seeds and F
0
seeds (seeds set after
crossing) were irradiated with 100, 200, 300, 400 and 500
Gy doses. The crossing block consisted of three rows of
female parents and two rows of male parents (raised two
weeks before the female parents to synchronize flower-
ing), spaced at 50
× 30 cm, during rabi 2006-2007. The
trial was conducted at Tamil Nadu Agricultural Univer-
sity, National Pulses Research Centre, Vamban Puduk-
kottai, Tamil Nadu. India.
Pollen fertility was analysed in the parents and their hy-
brids by acetocarmine staining technique
No. of viable pollen
Pollen fertility = --------------------------------------
× 100
Total no. of pollen observed
Cytological studies of parents and their hybrids were per-
formed. Flower buds (1-2 mm) were fixed in modified
Carnoy fluid (Ethyl alcohol : Chloroform : Glacial acetic
acid; 6 : 3 : 2, v/v) for 24 h, at 10-15
o
C, washed and pre-
served in 70% ethanol. For preparing slides, the anthers
were squashed in 2% acetocarmine and the slides were
slightly warmed and observed under a transmission mi-
croscope. The chromosome association at meiosis was
studied for the hybrids. Cells at diakinesis, metaphase
and anaphase were examined to obtain the frequencies of
univalents, bivalents and quadrivalents. Twenty five
PMCs were observed for estimating the frequencies of
chromosomal abnormalities.

Plant Mutation Reports, Vol. 2, No. 1, December 2008
34
Photomicrograhs were taken of the various abnormalities
observed in the hybrids.
Results
The results with normal (non-irradiated) crosses are pre-
sented in Table 1.
Table 1. Performance of normal interspecific crosses of Vigna radiata x Vigna umbellate*
Parents and Crosses PF (No.) PS (No.) PS (%) CSO
(No.)
CSG
(No.)
G (%) SAM
(No.)
HB (%) HL (%)
VBN1 × Vuy 550 12 2.40 55 35 63.64 22 62.86 37.14
VBN1 × Vur 660 14 2.12 149 110 73.83 80 72.73 27.27
VBN(Gg)2 × Vuy 700 18 2.50 40 28 70.00 15 53.57 46.43
VBN(Gg)2 × Vur 650 13 2.00 101 85 84.16 68 80.00 20.00
KM2 × Vuy 750 19 2.50 29 12 41.38 6 50.00 50.00
KM2 × Vur 820 35 4.26 27 12 44.44 6 50.00 50.00
K1 × Vuy 575 16 2.70 119 73 61.34 60 82.19 17.81
K1 × Vur 653 18 2.70 132 85 64.39 65 76.47 23.53
CO 6 × Vuy 625 20 3.20 125 68 54.40 45 66.18 33.82
CO 6 × Vur 628 24 3.80 139 79 56.83 61 77.22 22.78
VRM(Gg)1 × Vuy 750 28 3.70 127 102 80.31 93 91.18 8.82
VRM(Gg)1 × Vur 850 38 4.40 134 106 79.10 98 92.45 7.55
*: V. umbellata yellow = Vuy, V. umbellata red = Vur; PF = pollinated flowers; PS = pod set; CSO = Crossed seeds obtained; CSG
= Crossed seeds germinated; G = Germination; SAM = Seedlings attaining maturity; HB = Hybrid breakdown; HL = Hybrid lethal-
ity.
The maximum number of flowers emasculated and polli-
nated was 850 for the cross VRM(Gg)1 × Vur followed
by 820 flowers in the cross KM2 × Vur. The number of
pods set ranged from 12, in VBN1 × Vuy, to 38 in
VRM(Gg)1 × Vur. The percentage of pod set ranged
from 2.0 (VBN (Gg) 2×Vur) to 4.40 (VRM(Gg)1 × Vur).
The highest number of seeds, 149, was yielded by the
cross VBN 1 x Vur and the lowest, of 27 seeds, was pro-
duced by the cross KM2 × Vur. The pollen fertility per-
centage recorded in F
1
s was zero. The highest hybrid
germination was 84.16%, observed in the cross
VBN(Gg)2 × Vur and the lowest of 41.38% was recorded
in the cross KM2 × Vuy. The highest hybrid breakdown
of 92.45% was recorded in the cross VRM(Gg)1 × Vur,
and the highest hybrid lethality, of 50.00%, was observed
in crosses having V. radiata KM2 as female, whichever
the V. umbellata genotype used as male parent. The low-
est hybrid lethality (of 7.5%) was recorded for the cross
VRM(Gg)1 × Vur.
Table 2 gives the results observed in irradiated crosses.
The maximum number of flowers emasculated and polli-
nated was 900 in the cross VBN(G)2 (400Gy)
× Vuy
(400 Gy), followed by 895 flowers in the cross K1(500
GY)
× Vuy (500Gy). The number of pods set ranged
from 18 in five crosses, namely VBN (Gg)2 200Gy ×
Vuy (200 Gy), VBN (Gg)2 300Gy
× Vuy (300 Gy), KM2
(400GY)
× Vuy (400GY), CO6 (200 Gy) × Vuy (200
Gy) and VRM (Gg)1 (500Gy) × Vur (500 Gy), to 38 in
K1 (200 GY)
× Vuy (200 Gy). Percentage of pod set
ranged from 2.6 in the cross CO6 (200GY)
× Vuy
(200Gy) to 4.90 (VBN 1 (300GY)
× Vuy 300 Gy.
The highest number of seeds obtained was 80, for the
cross VRM(Gg)1 (500Gy)
× Vur (500Gy) and the lowest
number of seeds obtained was 6, for the cross VBN 1
×
Vur 500 Gy. The range of pollen fertility recorded in the
F
1
s was from 43% (VBN(Gg)2 300 GY × Vur 300 GY)
to 75% (VRM(Gg)1 100 Gy
× Vuy 100 Gy). The highest
germination recorded was 90.63% in cross VRM(Gg)1
200Gy
× Vuy 200Gy, and the lowest, at 28.57%, oc-
curred in cross CO6 (100Gy)
× Vuy 100 Gy. A hybrid
breakdown of 93.3% was observed in the cross
VRM(Gg)1 100Gy
× Vuy 100 Gy. Hybrid lethality
ranged from 60.00% for VBN(Gg)2 200 Gy
× Vur 200
Gy to 6.70%, recorded in cross VRM(Gg)1 100 Gy
×
Vuy 100 Gy.
To asses the reasons for the high pollen sterility in the F
1
,
the cytogenetic analysis through meiotic studies in PMCs
was carried out. The results are presented in Table 3. The
two parental species, V. radiata and V. umbellata had 2n
= 22 chromosomes and meiosis was normal with regular
formation of 11 bivalents. In F
1
of their cross, all types of
abnormalities were observed. Out of 25 PMCs studied at
Anaphase I, only one cell revealed 11 bivalents. The oc-
currence of abnormal associations, namely univalents and
quadrivalents, was frequently observed. The number of
univalents varied from 0 to 14, while the number of

Plant Mutation Reports, Vol. 2, No. 1, December 2008
35
quadrivalents ranged from 0 to 5. The average chromo-
some association per cell was IV (1.28) + II (4.96) + I
(6.96). Premature separation of chromosomes and forma-
tion of anaphase bridges was commonly observed in
many PMCs.
Table 2. Performance of irradiated interspecific crosses of Vigna radiata × Vigna umbellate (see Table 1 for abbreviations)
Parents and Crosses PF
(No.)
PS
(No.)
PS (%) CSO
(No.)
CSG
(No.)
G (%) SAM
(No.)
HB (%) HL (%)
VBN1 100 Gy × Vuy 100 Gy 700 28 4.0 0.0 0.00 0.00 0.0 0.0 0.0
VBN1 200 Gy × Vuy 200 Gy 750 30 4.0 0.0 0.00 0.00 0.0 0.0 0.0
VBN1 300 Gy × Vuy 300 Gy 710 35 4.9 0.0 0.00 0.00 0.0 0.0 0.0
VBN1 400 Gy × Vuy 400 Gy 750 35 4.7 0.0 0.00 0.00 0.0 0.0 0.0
VBN1 500 Gy × Vuy 500 Gy 725 32 4.4 0.0 0.00 0.00 0.0 0.0 0.0
VBN1 100 Gy × Vur 100 Gy 700 21 3.0 48.0 25.0 52.08 18.0 72.0 28.0
VBN1 200 Gy × Vur 200 Gy 722 21 2.9 45.0 21.0 46.67 16.0 76.2 23.8
VBN1 300 Gy × Vur 300 Gy 750 23 3.1 33.0 18.0 54.55 15.0 83.3 16.7
VBN1 400 Gy × Vur 400 Gy 720 31 4.3 8.0 3.00 37.50 2.0 66.7 33.3
VBN1 500 Gy × Vur 500 Gy 720 21 2.9 6.0 2.00 33.33 1.0 50.0 50.0
VBN(Gg)2 100 Gy × Vuy 100Gy 700 23 3.3 0.0 0.00 0.00 0.0 0.0 0.0
VBN(Gg)2 200 Gy × Vuy 200 Gy 650 18 2.8 0.0 0.00 0.00 0.0 0.0 0.0
VBN(Gg)2 300 Gy × Vuy 300 Gy 670 18 2.7 0.0 0.00 0.00 0.0 0.0 0.0
VBN(Gg)2 400 Gy × Vuy 400 Gy 900 35 3.9 0.0 0.00 0.00 0.0 0.0 0.0
VBN(Gg)2 500 Gy × Vuy 500 Gy 710 21 3.0 0.0 0.00 0.00 0.0 0.0 0.0
VBN(Gg)2 100 Gy × Vur 100Gy 755 23 3.0 28.0 11.0 39.29 6.0 54.5 45.5
VBN(Gg)2 200 Gy × Vur 200 Gy 675 25 3.7 35.0 15.0 42.86 6.0 40.0 60.0
VBN(Gg)2 300 Gy × Vur 300 Gy 520 28 3.8 38.0 12.0 31.58 6.0 50.0 50.0
VBN(Gg)2 400 Gy × Vur 400 Gy 568 20 3.5 0.0 0.00 0.00 0.0 0.0 0.0
VBN(Gg)2 500 Gy × Vur 500 Gy 685 28 4.0 0.0 0.00 0.00 0.0 0.0 0.0
KM2 100 Gy × Vuy 100Gy 870 35 4.0 0.0 0.00 0.00 0.0 0.0 0.0
KM2 2 200 Gy × Vuy 200 Gy 650 28 4.3 0.0 0.00 0.00 0.0 0.0 0.0
KM2 300 Gy × Vuy 300 Gy 589 19 3.2 0.0 0.00 0.00 0.0 0.0 0.0
KM2 400 Gy × Vuy 400 Gy 562 18 3.2 0.0 0.00 0.00 0.0 0.0 0.0
KM2 500 Gy × Vuy 500 Gy 556 19 3.4 0.0 0.00 0.00 0.0 0.0 0.0
KM2 100 Gy × Vur 100Gy 675 20 3.0 28.0 15.0 53.57 8.0 53.3 46.7
KM2 200 Gy × Vur 200 Gy 655 21 3.2 35.0 18.0 51.43 8.0 44.4 55.6
KM2 300 Gy × Vur 300 Gy 655 23 3.5 42.0 19.0 45.24 10.0 52.6 47.4
KM2 400 Gy × Vur 400 Gy 682 23 3.4 0.0 0.00 0.00 0.00 0.0 0.0
KM2 500 Gy × Vur 500 Gy 652 22 3.4 0.0 0.00 0.00 0.0 0.0 0.0
K1 100 Gy × Vuy 100Gy 655 22 3.4 0.0 0.00 0.00 0.0 0.0 0.0
K1 200 Gy × Vuy 200 Gy 855 38 4.4 0.0 0.00 0.00 0.0 0.0 0.0
K1 300 Gy × Vuy 300 Gy 845 39 4.6 0.0 0.00 0.00 0.0 0.0 0.0
K1 400 Gy × Vuy 400 Gy 745 28 3.8 0.0 0.00 0.00 0.0 0.0 0.0
K1 500 Gy × Vuy 500 Gy 895 35 3.9 0.0 0.00 0.00 0.0 0.0 0.0
K1 100 Gy × Vur 100Gy 875 35 4.0 25.0 10.0 40.00 8.0 80.0 20.0
K1 200 Gy × Vur 200 Gy 785 28 3.6 25.0 10.0 40.00 7.0 70.0 30.0
K1 300 Gy × Vur 300 Gy 885 35 4.0 28.0 10.0 35.71 7.0 70.0 30.0
K1 400 Gy × Vur 400 Gy 785 28 3.6 0.0 0.00 0.00 0.0 0.0 0.0
K1 500 Gy × Vur 500 Gy 655 21 3.2 0..0 0.00 0.00 0.0 0.0 0.0
CO 6 100 Gy
× Vuy 100Gy 700 19 2.7 0.0 0.00 0.00 0.0 0.0 0.0
CO 6 200 Gy × Vuy 200 Gy 700 18 2.6 0.0 0.00 0.00 0.0 0.0 0.0
CO 6 300 Gy × Vuy 300 Gy 755 21 2.8 0.0 0.00 0.00 0.0 0.0 0.0
CO 6 400 Gy × Vuy 400 Gy 786 25 3.2 0.0 0.00 0.00 0.0 0.0 0.0
CO 6 500 Gy × Vuy 500 Gy 785 25 3.2 0.0 0.00 0.00 0.0 0.0 0.0

Plant Mutation Reports, Vol. 2, No. 1, December 2008
36
Parents and Crosses PF
(No.)
PS
(No.)
PS (%) CSO
(No.)
CSG
(No.)
G (%) SAM
(No.)
HB (%) HL (%)
CO 6 100 Gy × Vur 100Gy 785 28 3.6 35.0 10.0 28.57 5.0 50.0 50.0
CO 6 200 Gy × Vur 200 Gy 650 25 3.8 38.0 12.0 31.58 6.0 40.0 60.0
CO 6 300 Gy × Vur 300 Gy 800 32 4.0 42.0 15.0 35.71 6.0 40.0 60.0
CO 6 400 Gy × Vur 400 Gy 725 22 3.0 0.0 0.00 0.00 0.0 0.0 0.0
CO 6 500 Gy × Vur 500 Gy 715 20 2.8 0.0 0.00 0.00 0.0 0.0 0.0
Discussion
In the present investigation, interspecific hybridization
was attempted between greengram and rice bean with the
aim of transferring useful traits from the wild relatives
into greengram. The extent of crossability, fertility of
hybrids and possibility of obtaining superior hybrids
through recombination of genomes were studied. The
wild relatives of greengram, such as V. umbellata, pos-
sess desirable genes for many yield components, coupled
with resistance to bruchids and MYMV. Transfer of these
genes into the cultivated species could result in develop-
ment of high yielding resistant types. The use of wild
Vigna accessions in greengram breeding has been prob-
lematic because of problems encountered in obtaining
successful F
1
hybrids due to crossability barriers. In spite
of these difficulties, wide hybridization between V. ra-
diata and its wild relatives was successfully accom-
plished by many workers (Ganeshram, 1993; Pandae, et
al., 1990; Renganayaki, 1985; Subramanian and Muthiah,
2000; Uma Maheswari, 2002). Crossability is a pre-
requisite for gene transfer in wide hybridization. Under-
standing crossability relationships among species has
been helpful in choosing methods to produce F
1
hybrids,
but also in tracing phylogenic relationships among spe-
cies.
Table 3. Meiotic behavior of chromatin in V. radiate x V. umbellate cross
Description I (Univalent) II (Bivalent) IV (Quadrivalent)
PMC 1 - 11 -
PMC 2 10 2 2
PMC 3 - 1 5
PMC 4 4 7 1
PMC 5 10 2 2
PMC 6 2 - 5
PMC 7 4 9 -
PMC 8 10 2 2
PMC 9 2 10 -
PMC 10 4 9 -
PMC 11 8 3 2
PMC 12 10 6 0
PMC 13 12 5 -
PMC 14 12 5 -
PMC 15 - 5 3
PMC 16 6 4 2
PMC 17 12 5 -
PMC 18 8 3 2
PMC 19 12 5 -
PMC 20 14 - 2
PMC 21 4 9 -
PMC 22 10 2 2

Plant Mutation Reports, Vol. 2, No. 1, December 2008
37
PMC 23 2 10 -
PMC 24 14 2 1
PMC 25 4 7 1
Total 174 124 32
Average chromosome association I
(6.96)
II
(4.96)
IV
(1.28)
In the present study, successful pod set was observed in
all 12 interspecific crosses with Vigna radiata as female.
This result is in agreement with previous reports (Ahuja
and Singh, 1977; Egawa, 1990; Gopinathan et al., 1986;
Mendioro and Ramirez, 1994; Parida and Singh, 1985;
Uma Maheswari, 2002).
The percentage of lethality among interspecific hybrids
varied from 6.70% to 60.00%. Similar observations on
hybrid lethality and inviability were noticed in interspeci-
fic crosses involving different wild Vigna accessions in
the past (Adinarayanamurty et al., 1993; Al-Yasiri and
Coryne, 1966; Chen et al., 1989; Ganeshram, 1993; Uma
Maheswari, 2002). Stebbins (1958) had attributed the
hybrid weakness, inviability, lethality and sterility as
mechanisms of nature for maintaining the integrity of
related species.
In general, the pollen fertility among the normal crosses
was zero compared to irradiated crosses, which indicated
that the mutational approach using irradiation is likely to
generate better fertile hybrids and segregants. Similar
results were reported by various authors for differential
pollen fertility among interspecific crosses of wild Vigna
accessions (Anandabaskaran and Rangaswamy, 1996;
Mendioro and Ramirez, 1994; Monika et al., 2001; Pan-
dae et al., 1990; Ravi et al., 1987; Sidhu and Satija 2003;
Subramanian and Muthiah, 2000; Uma Maheswari,
2002). Among crosses, pollen fertility was highest in the
cross V. radiata
× V. radiata var. sublobata, supporting
the view of Pandae et al., 1990 and Mendioro and Rami-
rez, 1994 that V. radiata var. sublobata is a probable pro-
genitor for V. radiata.
In normal crosses, the range of pollen sterility observed
in all the F
1
hybrids was high and no viable F
2
segregants
could be generated. Considering the importance of this
cross for the resistance related traits, it was essential to
device methods enhancing fertility in F
1
that could aid in
developing breeding materials with resistance, and cyto-
logical analysis was carried out for this hybrid. In irradi-
ated crosses, seed set was observed only for the lower
doses (100,200,300 Gy) of all crosses with V. umbellata
yellow.
Some of the hybrids that could be recovered from these
promising interspecific crosses might serve as better
breeding base for the improvement of yield and yield
components. Such interspecific hybrids were also re-
ported before (Ganeshram, 1993; Subramanian and Mu-
thiah, 2000; Uma Maheswari, 2002). In this situation,
selection for traits in early generations will not be fixable;
hence, selections in later generations or by adopting
modified breeding procedures such as inter-mating the
segregants followed by recurrent selection may shift the
gene action towards additive effects. Since sterility fac-
tors will be gradually reduced over generations in inter-
specific crosses and more recombined populations will be
available for selection, selection in the later generations
will be more effective.
Chromosomal analysis of V.radiata x V.umbellata F
1
hy-
brids and their parents revealed that chromosomal pairing
was normal in the parents, with 11 bivalents, whereas F
1
hybrids showed loose pairing between chromosomes
leading to precocious separation at Anaphase I. This had
already been observed by some of the earlier workers
(Bhatanagar et al., 1974; Kaur and Satija, 1998; Machado
et al., 1982; Uma Maheswari, 2002). Formation of univa-
lent, dicentric bridges and laggards also indicated lack of
homology between the parental species. The average as-
sociation of IV (1.28) + II (4.96) + I (6.96) indicated ab-
normal chromosomal association due to structural chro-
mosomal differences among parental genomes. For re-
storing fertility in this hybrid, adoption of chromosome
doubling through colchiploidy and recovery of fertile
amphidiploids would be a viable solution for recovering
useful segregants as suggested by Machado et al., (1982)
and Sidhu and Satija (2003).
Acknowledgement
The authors thank NBPGR, New Delhi, for providing the
wild Vigna species used in the interspecific hybridization
studies.
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