Simple cryopreservation protocol for Luffa pollen: enhancing breeding efficiency

This study aimed to develop a long-term pollen storage protocol for Luffa species (L. acutangula, L. cylindrica, L. echinata, and L. graveolens) and assess its potential for crop improvement. The optimal medium for in vitro pollen germination varied by species, with Brewbaker and Kwack (BK) medium with 10% sucrose suitable for L. acutangula, L. cylindrica, and L. echinata, and BK medium with 3% sucrose ideal for L. graveolens. Overestimation in staining tests compared to in vitro pollen germination was observed. The best results for cryopreservation were achieved with desiccation periods of 20, 30, and 40 min, maintaining moisture content between 14.04% and 18.55%. Pollen viability was negatively correlated with storage temperature (25, 4, and -20°C) and duration. Cryopreserved pollen at -196°C exhibited the highest viability over a prolonged period (2 months) and was comparable to fresh pollen in terms of germination, ovule fertilization, and fruit and seed set. This study presents a simple and reproducible pollen cryopreservation protocol applicable across Luffa species, facilitating long-term storage and its use in crop improvement efforts.

A Flow Cytometry-Based Assessment of the Genomic Size and Ploidy Level of Wild Musa Species in India

The genome size variation is an important attribute in evolutionary and species characterization. Musa L. is regarded as one of the taxonomically complicated genera within the order Zingiberales, with more than 75 species from wild seeded to seedless cultivars that may be diploid, triploid or tetraploid. The knowledge of total nuclear DNA content in terms of genome size and ploidy level in wild species of Musa is absolutely important in evolutionary and genomic studies.

METHODS

In this paper, chromosome spreading was performed via protoplast isolation and a fast air-dry dropping method and flow cytometry were used with Raphanus sativus L. (Brassicaceae) as a standard for ploidy and genome size estimation.

RESULTS

The results showed that genome size (2C) varied amongst Musa species, based on the ratio of G1 peak positions. The lowest genome size (2C) was found in M. balbisiana var. andamanica (1.051 ± 0.060 pg) and the highest genome size (2C) was recorded for Musa ABB.cv. Meitei-hei (1.812 ± 0.108 pg) for the section Eumusa. Among the species belonging to the section Rhodochlamys, M. rosae had the lowest 2C content of 1.194 ± 0.033 pg whereas the highest nuclear DNA content (2C) was observed in M. velutina (1.488 ± 0.203 pg). Cytogenetic analysis revealed that the chromosome number of 14 wild Musa species was 2n = 22, while 1 species-Ensete glaucum-showed a chromosome number of 2n = 18 (diploid), and for 3 species, the chromosome number was 2n = 33 (triploids). An association study based on the Pearson correlation coefficient showed 2C nuclear DNA content was significant and positively correlated with ploidy level (R = 0.9) and chromosome number (R = 0.84).

CONCLUSIONS

The present study provides reliable information on the genome size and ploidy level of wild Musa species from the Indian region through flow cytometric analysis, which could be further utilized in taxonomic and crop improvement programs. For the first time, the nuclear DNA content of eight wild diploid and three triploid Indian species were estimated and reported. Genome size could be an effective indicator in identification of species and evolutionary studies in Musa with varying ploidy levels and morphological similarities.

Histological and molecular insights in to in vitro regeneration pattern of Xanthosoma sagittifolium

A study on the effect of various phytohormonal combinations on in vitro propagation of Cocoyam [Xanthosoma sagittifolium (L.) Schott] was conducted to develop an improved and efficient in vitro regeneration protocol for its mass multiplication. Histological analysis to understand the in vitro regeneration pattern and genetic fidelity assessment of regenerated plants were also carried out. Single shoots excised from in vitro established cultures of X. sagittifolium were used as explants. Among the 32 different phytohormonal combinations tested, indirect organogenesis with intervening callus phase was observed on majority of the media combinations. Meristematic clump formation was optimally achieved on all the tested media combinations with maximum 43.54 ± 0.51 shoot primordia on MS medium containing 0.2 mg/L BAP + 0.1 mg/L NAA followed by 36.44 ± 0.76 shoot primordia on MS medium having 2.5 mg/L TDZ. Micro-morphological analysis of different morphogenetic structures revealed that the regeneration of cocoyam is well executed via meristematic nodules, shoot primordia formation that may evolve in to proper shoots. Adventitious shoots (> 2 cm) were successfully (100.00 ± 0.00%) rooted on the half-strength MS medium containing IBA (0.05-1.0 mg/L) and IAA (0.05-0.5 mg/L). The number of roots ranged from 0.78 ± 0.31 on the control half-strength MS medium to 13.94 ± 0.46 on half-strength MS supplemented with 1.0 mg/L IBA. Considering somaclonal variations as a potential restriction to in vitro multiplication of plants, genetic stability was assessed using 40 ISSR primers. The PCR amplification profiles obtained from all the tested propagules (calli, meristematic clumps, regenerated plantlets) were similar to the mother plants indicating the homogeneity of the individuals raised through the regeneration protocol reported here.

Transcriptome Profiling during Sequential Stages of Cryopreservation in Banana (Musa AAA cv Borjahaji) Shoot Meristem

Cryopreservation approaches have been implemented in gene banks as a strategy to back up plant genetic resource collections that are vegetatively propagated. Different strategies have been employed to effectively cryopreserve plant tissue. There is little information on the cellular processes and molecular adjustments that confer resilience to the multiple stresses imposed during a cryoprotocol. In the present work, the cryobionomics of banana (Musa sp.), a non-model species, was investigated through the transcriptomic approach using RNA-Seq. Proliferating meristems of in vitro explants (Musa AAA cv 'Borjahaji') were cryopreserved using the droplet-vitrification technique. Transcriptome profiling analysis of eight cDNA libraries including the bio-replicates for T0 (stock cultures (control tissue), T1 (high sucrose pre-cultured), T2 (vitrification solution-treated) and T3 (liquid nitrogen-treated) meristem tissues was carried out. The raw reads obtained were mapped with a Musa acuminata reference genome sequence. A total of 70 differentially expressed genes (DEGs) comprising 34 upregulated and 36 downregulated were identified in all three phases as compared to control (T0). Among the significant DEGs (>log FC 2.0), during sequential steps, 79 in T1, 3 in T2 and the 4 in T3 were upregulated and 122 in T1, 5 in T2 and 9 in T3 were downregulated. Gene ontology (GO) enrichment analysis showed that these significant DEGs were involved in the upregulation of biological process (BP-170), cellular component (CC-10) and molecular function (MF-94) and downregulation of biological process (BP-61), cellular component (CC-3) and molecular function (MF-56). The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that DEGs were involved in the biosynthesis of secondary metabolites, glycolysis/gluconeogenesis, MAPK signaling, EIN 3-lke 1 protein, 3-ketoacy-CoA synthase 6-like, and fatty acid elongation during cryopreservation. For the first time, a comprehensive transcript profiling during four stages of cryopreservation in banana were carried out, which will pave the way for devising an effective cryopreservation protocol.

Cryopreservation of pollen of Abelmoschus moschatus Medik. subsp. moschatus as an aid to overcome asynchronous flowering for wide hybridization with cultivated Okra [A. esculentus (L.) Moench]

BACKGROUND

Asynchronous flowering is one of the major constraints for hybridization between Abelmoschus moschatus subsp. moschatus, a wild species closely related to cultivated okra [A. esculentus (L.) Moench]. Availability of viable pollen is a prerequisite to facilitate breeding in these species.

OBJECTIVES

Pollen cryopreservation was attempted in A. moschatus subsp. moschatus, to overcome the asynchronous flowering barrier during wide hybridization with A. esculentus.

MATERIALS AND METHODS

Viability of fresh pollen of A. moschatus subsp. moschatus was assessed using acetocarmine and triphenyl tetrazolium chloride (TTC) test and in vitro germination by sitting drop culture method. Pollen of 10 accessions were stored at four temperatures (25, 4, -20 and -196 degree C), in the dark and periodically monitored for viability. The standardized cryopreservation protocol was applied to 24 accessions of A. moschatus subsp. moschatus over three months. In vivo pollen germination of 24 accessions of cryopreserved pollen and its efficacy on fertilizing A. esculentus cv 'Pusa Sawani' were recorded and pollen was utilized for hybridization with A. esculentus.

RESULTS

Brewbaker and Kwack medium with 15% sucrose was optimal for in vitro pollen germination. Pollen viability assessed by in vitro germination (60-90 %) was more reliable compared to acetocarmine (90-99 %) and TTC (85-99 %) staining tests. Significant negative correlation was found between pollen germination, storage time and temperature (25, 4 and -20 degree C) in all the accessions. Cryopreserved (-196 degree C) pollen showed significantly higher viability compared to all the other storage conditions, without viability loss. Successful pollination, fruit and seed set was observed in four out of 24 cross combinations attempted.

CONCLUSION

The cryopreservation of pollen of A. moschatus subsp. moschatus and its fertilizing ability offers great potential for a successful wide hybridization programme in okra.

Role of heterotrophic aerobic denitrifying bacteria in nitrate removal from wastewater

With the increase in industrial and agricultural activities, a large amount of nitrogenous compounds are released into the environment, leading to nitrate pollution. The perilous effects of nitrate present in the environment pose a major threat to human and animal health. Bioremediation provides a cost-effective and environmental friendly method to deal with this problem. The process of aerobic denitrification can reduce nitrate compounds to harmless dinitrogen gas. This review provides a brief view of the exhaustive role played by aerobic denitrifiers for tackling nitrate pollution under different ecological niches and their dependency on various environmental parameters. It also provides an understanding of the enzymes involved in aerobic denitrification. The role of aerobic denitrification to solve the issues faced by the conventional method (aerobic nitrification-anaerobic denitrification) in treating nitrogen-polluted wastewaters is elaborated.