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The present investigation entitled “Establishment of genetic fidelity in
micropropagated Robusta (Musa AAA) plants” was carried out at the Department of
Plant Breeding and Genetics, Rice Research Station, Vyttila, from September 2020 to
October 2021. The study was aimed to assess the genetic fidelity of in vitro propagated
banana plants of variety ‘Robusta’ generated by direct organogenesis for ensuring
supply of quality planting materials without somaclonal variations. Even though
molecular markers are precise and robust method for estimating genetic fidelity, it can
only provide information regarding the markers used in the study. So, the work was
extended to field level investigation which can be used for validation of molecular
analysis. The qualitative and quantitative observations were not restricted to early
stages but extended till harvest to make the comparisons to answer farmers concerns,
not just to make inferences.
One of the qualitative characters studied, ‘bract apex shape’ showed variation
in plants derived from subculture S11. It had ‘obtuse’ shaped bract while others had
bract shape specified as ‘intermediate’. Other characters compared in the study showed
no variation among subcultures. Even though majority of characters were uniform in
subcultures from S6 to S11, character modification occurred in S11 for bract apex shape
reflects possibility for epi-genetic changes. Significant difference was observed in the
subculture S11 from others used in the study for characters - plant height (cm),
pseudostem diameter (cm), leaf blade length (cm), leaf blade width (cm), male bud
length (cm), male bud circumference (cm), fruit length (cm), number of hands per
bunch, number of fingers/hand and bunch weight (kg). All the subcultures showed
uniformity for characters - number of leaves, fruit circumference (cm), fruit peel
thickness (mm), brix (%) and number of suckers. Out of the 15 characters studied, 10
were showing significant deviation in S11.
Two groups were formed based on the sample data from field analysis.
Subcultures ranging from S6 to S10 represented one group and S11 was the solo
representative of the other group. The mean for all quantitative characters studied was
found higher in group which had subcultures from S6 to S10. Subculture S11 was
observed as an outlier which joined with the same cluster of other subcultures which
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are closely related at a higher genetic distance. Similarity for results in ANOVA and
D
2
analysis confirmed that the subcultures with non-significant differences in ANOVA
were having negligible divergence for quantitative characters and maintained true-totype clonal behaviour in field for the important characters including yield and fruit
specifications.
Genetic similarity matrix constructed based on simple matching coefficient
confirmed molecular level uniformity of subcultures S6 to S10 for the screened
markers. The similarity matrix of S11 was clearly found separate from other
subcultures. Similarity dendrogram constructed based on UPGMA revealed the
separation of S11 cluster away from the clusters of subcultures S6 to S10 placed
together. Similarity in results obtained from fields and molecular analysis confirmed a
genetic base for variations occurred in S11.
The targeted gene specific SSR primers used in the study revealed the
polymorphism happened in subculture S11 for markers associated with genes SPL and
AP2/EREBP. The error caused in these genes can result delay in phase transition,
abnormalities in fruit characters and can induce higher susceptibility to abiotic stress.
Similar responses observed in field was in close agreement with the trait-based
polymorphism detected in molecular level.
Even though true-to-type clones are produced up to ten subcultures, considering
the random occurrence of mutation and verification of somaclonal variations associated
with higher level of subcultures, the investigation suggests that the subculturing can be
safely carried up to subculture 9 for ‘Robusta’ plantlets produced by direct
organogenesis. Potential for S10 subculture can be further clarified with use of more
molecular markers.