Identification of Novel Resistance Gene Sources to Cowpea Aphid (Aphis craccivora Koch) in Cowpea (Vigna unguiculata L.)
The development of cowpea aphid larvae was monitored on seven cowpea genotypes (IAR-48, TVu-15866, IT84S-2246-4, SAKA BABBA SATA, IT90K-76, KANANNADO and TVX 3236). The aim of the study was to determine the developmental response of the larvae as an indication of antibiotic resistance of the genotypes. Highly significant differences (p<0.01) were observed with respect to fertility, larval development, adult longevity, life span, multiplication rate and intrinsic rate of increase. KANANNADO and TVX 3236 show minimum antibiotic effects while a landrace SAKA BABBA SATA shows relatively high antibiotic effects. This result further reveals the potential of SAKA BABBA SATA as a resistance source to aphid. The reaction of IT84S-2246-4, a hitherto aphid resistant genotype, which supported higher levels of survival of the larvae relative to other known susceptible genotype IAR-48, may be an indication of the presence of a new biotype of Aphis craccivora endemic to Zaria environs, or that of the ability of insects to overcome hindrances to their survival including various forms of resistance.
Received: December 04, 2012;
Accepted: February 15, 2013;
Published: April 04, 2013
Cowpea (Vigna unguiculata L. Walp. Subsp. Unguiculata Fabaceae)
is one of the most important food and forage legumes in the tropics. Cowpea
is grown on 10.5 million ha, with an annual grain production of about 5.5 million
It is mainly cultivated for the seeds, however other important products from
it include the pods (fresh or dried) and leaves (Duke, 1990).
By far Nigeria is the biggest producer of cowpea, followed by Niger republic,
Burkina Faso and Ghana. Cowpea is however devastated by many biotic and abiotic
stresses. Prominent among the biotic constraints are various types of insect
pest and one of the key insect pest of cowpea is the cowpea aphid, especially
at vegetative stage (also infest at reproductive stage). It primarily infests
seedlings and causes damage directly by removal of sap from the plant and indirectly
through transmission of Aphid Borne Mosaic Viruses (ABMV). Aphids also cause
damage through secretion of honeydew which promotes growth of sooty moulds and
other fungal growth on leaves, thereby reducing photosynthetic efficiency of
the plant (Annan et al., 1996). Resistance to
insect pests in cowpea has been extensively studied. Most cowpea accessions
have been screened for resistance to the major insect pest. High to moderate
level of resistance has been reported for some of the pests, including cowpea
aphids (Singh et al., 1997) and many different
levels of these resistances have incorporated into several genotype. Similarly,
the genetics of aphid resistance has been studied in some of the resistant cultivars.
Two independent and non-allelic genes control the expression of resistance (Pathak,
1988, Myers et al., 1996). However these
studies were limited to few of the already identified resistance sources. Also
data from genetic crosses showed that more than locus may be involved in the
expression of the resistance (Githiri et al., 1996).
Therefore, further studies are needed to cover more resistant sources. IT84S-2246
derived its resistance to cowpea aphids from Tvu 1190 (Singh
and Singh, 1992). According to B. B. Singh, TVU 1190 and TVu 3000 have genes
for aphids resistance that do not segregate for aphid reaction (Myers
et al., 1996). However, in the routine cowpea program in cowpea section
of the IAR, it was observed that IT84S-2246 and lines derived from it show susceptible
reaction to aphids. Therefore, it is also necessary to investigate these lines
to confirm the presence of resistance or otherwise. This study reports the possibility
of the presence of variants of aphids (in Zaria) that are able to attack known
MATERIALS AND METHODS
Genotypes and study area: Seven genotypes (SAKA BABBASATA, TVU 15866,
IT90K-76, IT84-2246, IAR-48, TVX 3236 and KANANNADO) were obtained from cowpea
section of Institute for Agricultural Research, Ahmadu Bello University and
Zaria (11010 00N 07038 00E).
These genotypes were identified based on the preliminary evaluation were SAKA
BABBASATA (a local line), TVU 15866 and IT90K-76 turn out to indicate some level
of resistance while IT84S-2246 shows an unprecedented level of aphid support.
IAR-48 and TVX 3236 are improved aphids susceptible lines and KANANNADO is a
susceptible local line.
Experimental design: Each genotype was sown in pots filled with soil
in insect-proof cages in the screen house. There were three replications in
a Randomized Complete Design (RCD).
A single aphid was placed on each plant for each genotype. After the release
of two larvae the mother aphid along with any other larvae were removed. The
newly hatched larvae were maintained to produce the second-generation larvae.
A single aphid of this generation was subsequently observed daily to determine
the duration of larval stage, the duration of reproductive life and the total
number of larvae produced (fertility). These were used to calculate Multiplication
Rate (MR) and the intrinsic rate of natural increase (rm), using the following
(Asin and Pons, 2001), where, Fe = effective fertility
= number of larvae produced during a period equivalent to Tpr and Tpr = pre-reproductive
time = number of days from the birth of the aphid until production of the first
larva. The data obtained was analyzed to compare the genotypes in terms of larval
development. In either case the data analysis was carried out using the SAS
The analysis of variance result for the reaction of aphids is presented in
Table 1. The result of the analysis showed highly significant
differences (p<0.01) for fertility, larval development, adult longevity,
intrinsic rate of increase and multiplication rate of aphids in the seven genotypes
Aphid fertility was highest on KANANNADO with 62.0 larvae and lowest on IT90K-76
with 26.7 larvae (Table 2) while the mean fertility was 43.6
larvae. Similarly, IT90K-76 showed the maximum hindrance to larval development
with 9.0 day for larval development. The shortest duration was 6.0 days in KANANNADO
and TVX 3236 while the mean was 7.8 days. The mean adult longevity was 17.3
days with aphids surviving on IT90K-76 for a maximum of 10.0 days and the longest
days was 24.3 days in TVX 3236. The average life span of the aphids was 25.14
days. Aphids survived longest on TVX 3236 (30.3 days) and the shortest number
of days was 19.0 days in IT90K-76. The multiplication rate was highest on KANANNADO
and lowest on IT90K-76. Similarly, highest the intrinsic rate of increase was
0.225 on KANANNADO and the lowest of 0.117 on IT90K-76. The mean of intrinsic
rate of increase was 0.17.
|| Mean squares of development parameters in seven genotypes
|| Mean values of development parameters of aphids in seven
|Means with the same letters are not significantly different
The result of analysis of variance indicate significant differences (p<0.05)
in fertility, larval development, adult longevity, intrinsic rate of increase
and multiplication rate of aphids in the seven genotypes studied. Many workers
have used this method to determine resistance (especially by antibiosis) particularly
when all genotypes support the infestation by aphids as noted in this study.
Laamari et al. (2008) reported significantly
lower fertility, multiplication rate and duration of reproductive life and longer
duration of larval development on some landraces of broad bean to indicate antibiosis-mediated
resistance to aphids. Similarly Obopile and Ositile (2010)
reported that fecundity; survival and intrinsic rate of natural increase, pre-reproductive
period and relative growth rate of cowpea aphid differed significantly among
resistant and susceptible varieties of cowpea and further stressed the importance
of using these parameters as useful means of characterizing aphid resistance
in plants. Similar results were reported by Ofuya (1988);
Annan et al. (1997), Le
Roux et al. (2004) and Hafiz and Damarany (2006).
This result further revealed a new dimension to resistance of cowpea genotypes
to cowpea aphids. Genotypes known to be resistant show similar reaction as others
known to be susceptible. An established susceptible genotype IAR-48 had similar
level of response as IT84S-2246-4. Indeed it supported higher larval development
than IAR-48. On the other hand, TVU-15866, IT90K-76 and a landrace SBS had the
greatest level of hindrances to aphid development. It is worthy of notice that
IT90K-76 derived it resistance gene from IT86-2246-4, TVU-15866 was brought
from Kenya and SBS is a local line. These discrepancies observed in the reaction
of the genotypes may suggest a gap in our present knowledge of genetics of aphid
resistance in cowpea. Probably there is the existence of modifier to gene for
aphid resistance as studies by Myers et al. (1996)
tend to suggest. In the same vain, there is the possibility of the presence
of the presence of different biotypes of A. craccivora in Zaria. There
have been reports of the presence different aphid biotypes in Africa (Ombakho
et al., 1987; Martyn, 1991) but so far there
was not such report in Nigeria. Similarly most aphid resistant cowpea genotypes
developed at IITA have been reported to be susceptible in other countries (Messina
et al., 1985; Ofuya, 1997). Kusi
et al. (2010) recently reported high susceptibility of IITA lines
and suggested the existence of cowpea aphid biotype in northern Ghana which
is more virulent than the Nigerian biotypes. It is not clear how an anholytic
species like the cowpea aphid suddenly produces variant biotypes. Nevertheless,
rare mutations, chromosomal rearrangement and mitotic recombination may give
rise to new variants (Hales et al., 1997). Another
possible source of different biotype could be the unrestricted movement of research
materials from one part of the country to another and beyond. Therefore there
is the need to conduct further studies to ascertain cowpea aphid types in and
The susceptibility of IT84S-2246-4 indicates the possibility that there is
a new variant of cowpea aphid that is capable of infesting known resistances
sources. Two genotypes, IT90K-76 and the local line SAKA BABBA SATA were identified
as a possible resistance sources because the highest level of antibiosis was
recorded with these genotypes. The landrace, SAKA BABBA SATA, has a great potential
as sources of additional resistant gene against the Cowpea aphids in Zaria and
beyond. This further highlight the importance of local line as potential sources
of useful genes for the genetic improvement of crop plants.
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