In vitro regeneration and salinity tolerance studies on monoand poly-embryonic mango (Mangifera indica L.) genotypes
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Date
2022
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DIVISION OF FRUITS AND HORTICULTURAL TECHNOLOGY, ICAR-INDIAN AGRICULTURAL RESEARCH INSTITUTE, NEW DELHI 110 012
Abstract
The present study was carried out to standardize the in vitro regeneration protocols
through both the direct and indirect methods using nucellus tissue as explant in mango. Six mango
genotypes including three from mono- (Amrapali, Dashehari and Pusa Arunima) and three polyembryonic (Kurakkan, Olour and K-2) type were used. Later on, screening protocols for salinity and
drought; and in vitro mutagenesis using callus culture were also standardized. Various changes
associated with the callus growth and physico-biochemical parameters under the salinity,
moisture (drought) stress and in vitro gamma irradiation were also studied. For callus induction,
basal media [Macro-salts of B5, micro-salts and organics of MS, FeNa2EDTA (MS), sucrose (60%;
w/v), L-Glutamine (400 mg/l), caesin hydrolysate (200 mg/l), activated charcoal (200 mg/l), agar (8
mg/l)] along with 2,4-D (18.08 µM) + Benzyl adenine (2.22 µM) was observed as the best
combination. Similarly, for conversion of callus into the somatic embryos basal media
supplemented with thidiazuron (4.54 µM) was recorded as the best. The earliest (52.50 days) and
highest (72.57%) somatic embryogenesis was observed in the polyembryonic genotype ‘K-2’. For the
maturation of somatic embryos a combination of basal media + BAP (4.44 µM) + ABA (3.78
µM); and for germination of the matured somatic embryos basal media + BA (2.22 µM) + GA3
(2.89 µM) was observed as the best. Among the six germination media (GM), GM 2 [BA (2.22
µM) + GA3 (2.89 µM)] took the shortest (29.56 days) duration to germinate; along with having
the highest germination (38.33%). Amongst the genotypes, the earliest (36.87 days) and highest in
vitro somatic embryo germination (31.30%) was observed in the K-2, followed by Kurakkan (40.03
days, 25.46%). The in vitro regenerated plantlets were successfully hardened ex vitro using Cocopeat,
Perlite and Vermiculite (1:1:1). Clonal fidelity assessment using the SSR markers showed the absence
of any somaclonal variation in the in vitro regenerated plantlets. Irrespective of the media
combination, somatic embryogenesis and plantlet regeneration in mango was observed as highly
genotypic specific and the polyembryonic were more responsive as compared to the monoembryonics.
Probit analysis of callus mortality (%) was used to estimate the LD50 values. For salinity (NaCl)
screening, the highest LD50 was in Kurakkan (53.085 mM), followed by Olour (50.045 mM), K-2
(33.214 mM), Dashehari (38.867 mM) and Amrapali (28.940 mM). For drought [PEG 6000 (%;
w/v)], the LD50 values in decreasing order were-Olour (16.33%), Kurakkan (13.73%), K-2 (11.66%),
Amrapali (6.47%) and Dashehari (5.69%). For gamma irradiation, the highest LD50 was in Kurakkan
(87.613 Gy), followed by Dashehari (79.644 Gy), Amrapali (55.083 Gy), K-2 (51.383 Gy), while the
lowest was in Olour (29.831 Gy). As evident from the results, there was significant impact of the salt
(NaCl) induced salinity stress and PEG induced moisture stress on various growth and biochemical
parameters of callus of five mango genotypes. Exposure to gamma irradiation also significantly
reduced the survival (%) of the mango calli. Under the above stress conditions, there was increase in
the content of callus MDA, total phenols, total soluble proteins and osmolytes like proline and total
soluble sugars. The activities of anti-oxidant enzymes (CAT, SOD, POD and GR) also followed
increasing trend upon exposure to the NaCl or PEG 6000 or gamma irradiation. Based on the results,
the five mango genotypes in decreasing order of salinity (NaCl) tolerance were Kurakkan > Olour >
K-2 > Dashehari > Amrapali. Similarly, the decreasing order for PEG 6000 induced drought tolerance
was Olour > Kurakkan > K-2 > Amrapali > Dashehari. The results of this study can be used for in
vitro screening and selection for salinity/ low moisture stress tolerance in other mango genotypes,
somaclones, in vitro induced mutants etc.