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Phylogenetic relationships of Indian Citron (Citrus medica L.) with other important Citrus species have been inferred through sequence analyses of rbcL and matK gene region of chloroplast DNA. The study was based on 23 accessions of Citrus genotypes representing 15 taxa of Indian Citrus, collected from wild, semi-wild, and domesticated stocks. The phylogeny was inferred using the maximum parsimony (MP) and neighbor-joining (NJ) methods. Both MP and NJ trees separated all the 23 accessions of Citrus into five distinct clusters. The chloroplast DNA (cpDNA) analysis based on rbcL and matK sequence data carried out in Indian taxa of Citrus was useful in differentiating all the true species and species/varieties of probable hybrid origin in distinct clusters or groups. Sequence analysis based on rbcL and matK gene provided unambiguous identification and disposition of true species like C. maxima, C. medica, C. reticulata, and related hybrids/cultivars. The separation of C. maxima, C. medica, and C. reticulata in distinct clusters or sub-clusters supports their distinctiveness as the basic species of edible Citrus. However, the cpDNA sequence analysis of rbcL and matK gene could not find any clear cut differentiation between subgenera Citrus and Papeda as proposed in Swingle's system of classification.

The study of the seed storage behavior and cryopreservation of embryonic axes was attempted in Citrus jambhiri genotypes using air desiccation-freezing, vitrification, and encapsulation-dehydration methods. Seeds of this species revealed nonorthodox seed storage behavior with moderate seed longevity and sensitivity to desiccation and freezing. Successful cryopreservation was achieved with all three methods using embryonic axes; however, the recovery growth percentage significantly differed among these methods. Cryopreservation was efficient for the embryonic axes desiccated to 13%-15% moisture content. Freezing of embryonic axes at this moisture content in liquid nitrogen showed a good recovery rate of 40%-50%. In the vitrification method, embryonic axes subjected to PVS2 treatment for 40 min had the highest recovery rate of 25% after cryopreservation. In the encapsulation-dehydration method, encapsulated axes precultured on 0.5 M sucrose medium followed by 6 h of desiccation had the highest recovery growth of 30%-60% after cryopreservation. Out of the three methods employed, the encapsulation-dehydration method gave the best recovery values for embryonic axes. High regeneration values of embryos in comparison to embryonic axes prompted us to undertake large-scale cryobanking of C. jambhiri using embryos (seeds without seed coats) and more than 100 accessions of C. jambhiri have been cryostored in the national cryobank. This would further serve the purpose of conserving nucellar embryos with zygotic embryos.

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