Abstract:

Groundnut rosette disease (GRD) is the most destructive virus disease of Valencia
groundnuts (Arachis hypogaea L.) in Africa. To widen the germplasm base of Valencia
types grown in Uganda, two exotic Valencia lines namely, NuMex-M3 and Valencia C,
National Semi-Arid Resources Research Institute (NaSARRl) but they succumbed to the
disease. Sources of GRD resistance were found in Spanish and Virginia types, which
could complicate genetic improvement of Valencia type of groundnuts due to lack of
information on the genetics of GRD resistance on the available breeding lines. This study
ii) To determine gene action controlling resistance to GRD in Valencia groundnuts and
iii) To evaluate F2 and backcross segregating populations for recovery of Valencia type
characteristics . Six crosses were made between; Valencia C (P|) x ICGV-SM 90704
(P2), Valencia C (P,) ICGV-SM 99566 (P2),
NuMex-M3 (Pi)
ICGV-SM 99566 (P2), to generate Fi, F2, BC,P| and BC,P2
populations.The parents (Piand P2) together with F|, F2, BC|Pi and BC|P2 populations of
GRD severity were collected on a 1-9 score scale. Phenotypic Coefficient of Variation
(PCV), Genotypic Coefficient of Variation (GCV), Genetic Advance as percent of Mean
performed to determine the type of gene effects controlling GRD resistance. Cluster
analysis was performed morphological descriptors and similarity
xi
was conducted (i) To determine heritability for resistance to GRD in Valencia groundnuts
(GAM) and heritability were estimated using variance components. Scaling tests were
x ICGV-SM 96801(P2), Valencia C (P,) x
each cross were evaluated in Randomised Complete Block Design (RCBD). Data on
x ICGV-SM 90704 (P2), NuMex-M3 x
were imported and evaluated for GRD by the Groundnut Improvement Program of
using data on
NuMex-M3 (Pi) x
ICGV-SM 96801 (P2), and
coefficients were generated between Valencia lines and their respective segregating
populations.
The PCV and GCV estimates were high (20.04-70.1%) in all the six crosses except for
Valencia C x ICGV-SM 96801(18.1%) and NuMex-M3
which exhibited moderate GCV values. Broad and narrow sense heritability estimates for
GRD disease score ranged from (64.1 to 73.7%) and (31 to 41.9%) respectively in all the
crosses. The GAM was high in all the crosses (21-50.7%) except for Valencia C x ICGVSM
96801 (14.67), M3 x ICGV-SM 99566 (18%) and NuMex-M3 x ICGV-SM 96801
(13.5%) crosses that exhibited moderate GAM.
The study reaveled three types of epistatic gene effects viz., additive
The component dominance
dominance [j] in Valencia Cx ICGV-SM 96801, NuMex-
ICGV-SM 99566
Valencia C and x ICGV-SM 99566 crosses. Opposite and significant signs of
duplicate epitasis in almost all the later crosses for GRD resistance.
The study revealed the presence of variability of GRD resistance, implying that genetic
improvement of these exotic materials is possible. Heritability and gene effect estimates
depended on the parental backgrounds that were used in the study. The presence of
duplicate epitasis in the crosses for GRD resistance revealed a complex nature of
inheritance of GRD resistance. Effective improvement of the materials under study will
require breeding efforts that exploits both additive and non-additive gene effects.
xii
M3x ICGV-SM 96801, NuMex- M3x ICGV-SM 90704, NuMex-M3 x
additive [i] and additive x
x additive [i],
x dominance [1] was more predominant than additive x
x ICGV-SM 96801(17.1%)
additive x dominance |j| and dominance x dominance [1] in control of GRD resistance.
dominance [d] and dominance x dominance [1] components indicated the importance of
I
The current study revealed high recovery (60-98% similarity coefficient) among the
populations and Valencia lines (NuMex-Mj and Valencia C), except for BCi ICGV-SM
96801 and F2 of NuMex-M3 x ICGV-SM-96801 and Valencia C x ICGM-SM 96801
crosses respectively. Such populations can be considered for further improvements.
Therefore, maximum gain in GRD resistance and Valencia trait recovery can be obtained
if only those populations that exhibited high resistance and Valencia trait recovery are
enhanced in the breeding program.