Abstract
Genetic variabilities among the genotypes of any species could be utilized for its improvement. PCR-based Random Amplified Polymorphic DNA (RAPD) technique was used to determine the genetic diversity and relationship among 10 cucumber varieties and genotypes. Five decamer primers were used to amplify genomic DNA and the primers yielded a total of 54 bands of which 36 bands were polymorphic and 18 bands were monomorphic. The UPGMA dendrogram based on Nei's (1972) genetic distance indicated segregation of 10 cucumber varieties and genotypes into two main clusters. Variety Joti alone grouped in cluster 1 while variety Green Master, Shahi-50, Shikha, Shila, Shital, Naogaon-5, Shohag-50, Giant Long and genotype CS-043 grouped in cluster 2. Variety Shila was very close to variety Shital with the least genetic distance (0.1712). The highest genetic distance (0.5352) was found between Joti and Naogaon-5. In vitro regeneration of cucumber through shoot tip culture was studied in order to establish an efficient and reproducible regeneration technique. Maximum number (3.82) and percentage (63.74 %) of explant regeneration were observed in variety Green Field. Interaction of Green Field and 3.0 mg/l BAP produced the highest number (6.52 and 19.05) of multiple shoots at second and third subculture, respectively. Regarding callus induction ability in different cucumber varieties, it was found that the highest number and percentage (6.00 and 99.99 %, respectively) of callus were obtained from variety Shital when either its leaf explants were inoculated in MS medium enriched with 1.0 mg/l NAA alone or internodal explants were cultured in medium supplemented with 1.0 mg/l each of NAA and BAP. The internodal explants of Green Field produced the highest callus weight (3.49 gm) when cultured on medium supplemented with with 3.0 mg/l NAA and 2.0 mg/l BAP and the lowest weight (0.99 gm) of callus was produced from nodal explants of the same variety in MS medium fortified with 3.0 mg/l NAA alone. For root induction, IBA was used. Maximum number of roots (19.54) and the longest (8.80 cm) roots were found in variety Shital and Shila, respectively on half strength MS medium fortified with 2.0 mg/l IBA. Regarding acclimatization of in vitro plantlets, maximum number Shital plantlets survived at ex vitro environment. Cent percent survivability was recorded in variety Shital when its plantlets were drenched with ridomil @ 1.0 mg/l. The regenerated cucumber plantlets were successfully hardened in polythene bags, then transferred in big earthen pots and finally established in big earthen pots. A protocol of Agrobacterium – mediated genetic transformation has been developed for the transfer of genes resistance to abiotic stress. The highest number (14.22) of leaf calli survived when those were inoculated in Agrobacterium tumefaciens suspension for 5 minutes and then kept in co-cultivation media for 48 hours. The highest number and percentage (4.04 and 67.38 %, respectively) of GUS +ve calli were obtained from the interaction of leaf explant x 5 minutes infection time x 48 hours co-cultivation period. The polymorphism detected in this study has the applicability to use in genetic improvement while the regeneration and transformation protocols have potential for use in gene transfer experiments in future studies.