Abstract
Orchids are the most important flowers grown commercially for cut flowers. The present study was conducted to investigate variation among orchids based on morpho-molecular characterization and postharvest studies on vase life of orchids. A total of nine experiments were conducted to achieve the objectives of the study. Study on morphological data of 25 orchids revealed highly significant variation among them. Further, morphological data were analyzed through univariate and multivariate techniques to assess genetic diversity. Morphological studies revealed significant variation in plant height, leaf area, flower spread, flower weight and number of flowers per plant, indicating additive gene action. Principal component analysis (PCA) and principal coordinate analysis (PCOA) showed maximum variation in plant height, leaf area, spikes per plant, spike length and flower weight among characters. Maximum inter orchid distance (5.808) was found between Mokara Orange and Oncidium crista while, minimum distance (0.397) was noticed between Dendrobium Earsakul and Dendrobium Kultana Blue. Non-hierarchical clustering formed five groups based on morphological characteristics. The data on path analysis revealed that plant height and number of spikes per plant had maximum positive direct effect (0.9510 and 0.4831, respectively) on flower number. Number of flowers had direct correlation with number of spikes per plant; leaf area was correlated with plant height and roots per plant indicating the importance of these characters as selection criteria for orchids. Molecular characterization using RAPD was conducted on thirty orchids to determine their genetic distances and relationships. Among different primers used for RAPD analysis, six primers showed polymorphism, which produced 43 scorable bands of which 40 were considered as polymorphic (92.75%). The highest value of similarity index was 1.00 between Dendrobium Violate White and Dendrobium Kultana Blue. The highest genetic distance (0.7885) was observed between Ascocentrum garayi vs Dendrobium Kultana Blue. Locus OPU10-5 and OPU10-6 showed highest level of gene diversity (0.5000) and Shannon information index (0.6931). The dendrogram resulting from Unweighted Pair Group Method using Arithmetic average (UPGMA) hierarchical cluster analysis separated orchids into seven distinct clusters at similarity coefficient value of 0.7885, implying a strong parallelism in genetic variability of orchids. The data acquired from this study could be used for identification and classification of other orchids. Studies on postharvest behavior of orchids showed that pulsing in 30 mM AgNO3 for 30 minutes and in 0.5 mM silver thiosulfate (STS) for 24 hrs at 22°C improved postharvest behavior and vase life of Dendrobium Sonia (30.28 days) and Mokara Dieheard Red (15.05 days). Oncidium crista in (R.) in 50 mM AgNO3 for 30 minutes enhanced vase life (19.16 days). Study on various holding solutions revealed that 30 mM AgNO3 + 225 mM HQC + 400 mM glucose significantly improved postharvest behaviors in Dendrobium Sonia and Mokara Dieheard Red while Oncidium crista (R.) responded best with 30 mM AgNO3 + 400 mM glucose followed by 4mM STS + 225 mM HQC + 400 mM glucose at 22°C. Pretreatment in 0.75 mM of 1-Methylcyclopropene (1-MCP) for 2 hour significantly improved postharvest behaviors of Dendrobium Sonia, while Vanda coerulea (G.) performed well in 0.5 mM 1-MCP at 25°C. Various packing materials showed that newspaper at 22°C could improve postharvest behavior in Vanda coerulea (G.) with vase life of 18.75 days, while Dendrobium Sonia performed well in brownpaper and newspaper packings (vase life 31.28 and 29.35 days, respectively). It can be concluded from the present study on morpho-molecular characterization that variations exist among studied orchid germplasm which can be used to differentiate those from each other and to understand the diversification mechanisms of species and lineages for research works on developing new varieties. Postharvest studies indicated that Dendrobium Sonia responded well than other orchids. In case of postharvest applications, pulsing or holding solutions could be applied to extend the vase life of orchids. However, for using these treatments to other orchids; their responses should be studied properly before application.