Morphogenetic Characterization of Kinnow Mutants

Abstract

The present investigation “Morphogenetic Characterization of Kinnow Mutants” was carried out at the Division of Fruits and Horticultural Technology, ICAR-IARI, New Delhi during 2016-2018. From the diverse mutated population of Kinnow mandarin, five-year-old putative mutants generated from various doses of gamma irradiation (15, 20, 25 and 30 Gy) and EMS (0.05%, 0.1%, 0.2% and 0.5%) were selected for the study and compared with the wild type (WT). The Kinnow mutants were characterized based on growth, yield, physiological, biochemical and fruit quality parameters over two successive years (at 5th and 6th year of tree age). They were further characterized using SSR markers. The mutants showed both stimulatory and inhibitory response with respect to various morpho-physiological and biochemical characteristics. Plant height and fruit yield were reduced by 49.65% and 65.91% in the mutant G-20 developed at 30 Gy. Compared to wild type (WT), leaf area was recorded maximum and minimum in the mutants G-6 and G-14 developed from 20 and 25 Gy. Photosynthetic pigments, chlorophyll a and b were degraded maximum in mutant G-20 (30 Gy), while total phenol was stimulated in G-18-G-20 (30 Gray). Proline accumulation was higher in G-14 and G-15 and total soluble protein (TSP) in G-15 (25 Gy). Antioxidant enzymes (SOD, CAT and POX) and glutathione reductase (GR) were up-regulated maximum in the mutants generated from 30 Gy. Fruit weight, fruit size, PAL and PME activity were observed differently in mutants. The desired low seeded mutants G-6 and G-9 were obtained with an average of 7-8 seeds/fruit developed at 20 Gy as compared to 31 seeds/fruit in the wild type. The juice recovery per cent in these mutants had parallel values with the wild type. Furthermore, irradiation treatment enhanced IAA content by 188.78-247.23% in the mutants G-7- G-9, while 79.57-93.46% enhancement in ABA content was assayed in the mutants G-6 and G-7 developed at 20 Gy. Phenological traits in the EMS induced mutants similar to the gammairradiated mutants exhibited both stimulatory and inhibitory responses. Plant height in the mutants E-2 and E-5 (0.05% EMS) was stimulated by almost 10% while it was inhibited by 25% in the mutants E-16 and E-17 created from 0.5% EMS. The plant height although was inhibited in E-16, the fruiting intensity as compared to WT was higher in the said mutant by almost two-fold. Almost 50% reduction in fruit yield was noted in mutants E-6 and E-8 (0.1% EMS). Leaf area was more in the mutants E-1 and E-2 (0.05% EMS) and was reduced in the mutants beyond 0.2%. Chlorophyll pigments a and b were observed maximum in the mutants E-1 and E-14 developed from two contrasting dosed of 0.05 and 0.2% EMS. Chlorophyll a:b ratio was however, lowest in the mutant E-14 (0.2% EMS). Both stimulatory and inhibitory response was observed in the magnitude of transpiration rate, stomatal conductance and leaf intercellular CO2 in the mutants developed from higher doses of EMS. The Photosynthetic rate was minimum in E-13 developed from 0.2% EMS. A correlated dose-dependent increase of almost two-fold was recorded in the total phenol, proline and total protein content in the mutants created from 0.2 and 0.5% EMS. The variation in traits of interest such as reduced plant height, succulent leaves with high RWC, stomatal conductance and upregulated antioxidant enzyme activity was significantly higher in the mutant E-16 created from 0.5% EMS. The number of seeds < 15 seeds/fruit was indexed in the mutants E-16 and E-19. The phytohormones IAA and ABA were assayed maximum in the mutant E-18 (0.5% EMS). In an attempt to characterize the putative mutants developed through different doses of gamma rays and EMS, thirty-four SSR markers were screened for polymorphism among the Kinnow mutants of which only two were found informative. 12 alleles were detected among two SSRs with an average of 6 alleles at per locus and the highest number of alleles (7) was recorded in SSR locus AMB2. The average diversity indices of SSR viz., allele frequency, gene diversity, expected heterozygosity and PIC were 0.415, 0.672, 0.415 and 0.611 respectively. The N-J tree was constructed based on the two SSRs data which clustered into two major groups. Subsequently, clusters were simplified into six clades which distinguished gamma irradiation and EMS based mutants which were reconfirmed through PCoA. First three axes of PCoA contributed 80.88% of the cumulative variation. The molecular variance (AMOVA) explained 42 % variation among the populations, 48 and 10 % variation among within and among the individuals respectively. The findings of the present study revealed that gamma irradiation and EMS have the potential to generate much-needed variation in Kinnow mandarin with noble traits which can be utilized for the selection of desirable mutants or can be used in the future breeding programme.