Genetic variability, path coefficient and marker-trait association analysis for resistance to rosette disease in groundnut.
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Date
2019-02
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Abstract
Several abiotic, biotic and socio-economic aspects constrain the production of groundnut
(Arachis hypogea L.). Groundnut rosette disease (GRD) which can cause yield losses of up
to 100% in susceptible cultivars, is among the most important biotic stresses. The use of
resistant cultivars is the most viable method to control the disease, therefore, breeding for
high yielding and GRD resistant cultivars is needed and should be a priority. The present
study was conducted to: (i) determine genetic variability for GRD response and yield traits in
selected groundnut accessions under natural infestation, (ii) assess the relationship between
seed yield and its related traits, and analyse agro-morphological diversity in selected
groundnut accessions under natural GRD infestation and (iii) evaluate groundnut recombinant
inbred lines for resistance to GRD and perform SNP marker-trait association analysis. Twentyfive
groundnut accessions and three controls were evaluated under natural GRD infestation
to assess genetic variability for GRD response and yield related traits. Seed yield, number of
pods per plant, plant height, GRD incidence and number of secondary branches showed high
phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (GCV), while
moderate variation (PCV and GCV) was observed for days to flowering and pod width. A
combination of high heritability and genetic advance was recorded for number of secondary
branches, plant height, seed yield and GRD incidence, indicating that phenotypic selection based on the mean would be successful in improving these traits. Phenotypic correlations and
sequential path analysis indicated that high seed yield was directly associated with taller
genotypes, higher number of pods per plant and hundred seed weight, which were a result of
higher pod width and lower GRD incidence. Based on morphological traits, the evaluated
accessions were grouped into four clusters. Days to flowering and maturity, number of
branches, plant height, number of pods per plant, pod width and length, seed yield and GRD
incidence, largely influenced this variation. Principal component analysis (PCA) biplot was
effective in showing the genetic distance among the accessions with results consistent to
those of the cluster analysis. Moreover, Shannon-Weaver diversity indices (0.949-0.9996) for
qualitative traits also indicated the existence of high diversity among the accessions. A total
of 25 groundnut genotypes, which comprised 21 RILs derived from a bi-parental cross, both
parents, and two susceptible controls (CG7 and JL24) were evaluated and used to perform
SNP marker-trait association analysis for resistance to GRD. There were significant
differences among the lines in all recorded traits, indicating the existence of genetic variability
and possibility of effective selection. Interaction of genotype and environment was significant
for disease incidence and the glasshouse environment had higher disease pressure, providing
the best discrimination among the tested genotypes. ICGV-SM 15605, ICGV-SM 15621, ICGV-SM 15618, ICGV-SM 15604 and ICGV-SM 15615 were among the resistant and high
yielding RILs. Twenty-two highly significant marker-trait associations were identified, which
will add to previously reported genomic regions influencing GRD and the aphid vector
resistance. Overall, the study showed that taller genotypes, higher number of pods per plant
and hundred seed weight can be used to improve seed yield in groundnut, particularly under
GRD infestation. The genetic diversity among the accessions provides an opportunity for
parent selection that can be used for breeding high yielding and GRD resistant cultivars. In
addition, the SNP markers will be useful in classifying groundnut germplasm based on the
GRD response and for their use in marker-assisted selection, once validated.
Description
Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.