DOI: 10.5091/plecevo.161947

Authors: D. Jithmi M. De Silva, B.D. Punsara Dharaka, K.M.G. Gehan Jayasuriya, Filip Vandelook

Abstract: Background and aims – Climate change is a significant global challenge affecting soil health and agriculture, including increased soil salinity levels. Certain salt-tolerant wild species can be considered for crop improvement and provide a solution to increasing salinization. We studied the inter-population variation in salt tolerance of Vigna marina seedlings, to explore the potential use of these wild resources to improve cultivated Vigna and for better conservation decisions. Material and methods – Inter-populational variation in salinity tolerance of seedlings of four different V. marina populations growing in different regions in Sri Lanka (Unawatuna, Mahamodara, Negombo, and Thalpe) was studied. Seedlings from seeds collected from these populations were grown under 0, 100, 1000, 2000, 10,000, and 20,000 ppm NaCl concentrations, following standard salinity tolerance test procedures. The plant performance was evaluated by measuring biomass, root: shoot ratio, height, growth rate, and chloride ion accumulation in leaves, stems, and roots. Finally, the performance of the V. marina populations was compared with two commercial varieties of Vigna radiata (MI6 and Ari), one of which was considered salt-tolerant. Key results – All seedlings showed reduced growth at 10,000 and 20,000 ppm NaCl concentrations. The Negombo population showed the highest total dry mass at 20,000 ppm, and seedlings from all populations survived at 20,000 ppm salt concentration, except those from the Mahamodara population. Overall, the Thalpe population performed best at 20,000 ppm. The highest salt accumulation was recorded in leaves and stems rather than in roots. Commercial V. radiata varieties did not survive the highest salt concentrations (10,000 and 20,000 ppm). Conclusion – Given that V. marina populations collected in different locations show considerable inter-populational variation in salinity tolerance, we recommend conserving multiple V. marina populations to cover the range in variability in salinity tolerance traits. Natural populations of V. marina exhibited better survival at high salinity levels as compared to the commercial salt-tolerant V. radiata varieties, highlighting the halophytic nature of V. marina, and its putative importance in developing Vigna varieties that can be cultivated in more saline conditions.

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DOI: 10.5091/plecevo.151630

Authors: Malaka Madhuranga Wijayasinghe, Kariyawasam Marthinna Gamage Gehan Jayasuriya, Savitri Gunatilleke, Nimal Gunatilleke, Jeffrey Walck

Abstract: Background and aims – Although viviparous seeds of mangrove species have traditionally been considered non-dormant, our previous study has shown that Aegiceras corniculatum, a crypto-vivipary species exhibits epicotyl dormancy. However, the kind of epicotyl dormancy in this species has not yet been explored. Thus, the aim of this study was to ascertain the kinds of epicotyl dormancy present in A. corniculatum. Material and methods – Mature fruits were collected in Sri Lanka. The effects of scarification, light, and temperature on root emergence and the effects of scarification, gibberellic acid (GA3), salinity, light, and root stability on shoot emergence were tested. In addition, the morphology and anatomy of the fruits in relation to shoot emergence and growth were documented. Key results – Under both light/dark and darkness, > 70% of non-scarified and scarified fruits had an emerged root within 30 days, and thus, we considered them non-dormant. Root emergence was dependent on temperature, with reduced root emergence at higher temperatures. In contrast, a substantial time delay occurred between root and shoot emergence. Environmental conditions influenced shoot emergence, with emergence slower (1) in low NaCl solutions than in high solutions, (2) in darkness than in light/dark, and (3) when fruits were laid horizontally on a substratum as compared to being planted vertically. When fruits were treated with GA3 or were scarified, the time delay between root and shoot emergence was shortened. Conclusion – Since fruits of A. corniculatum contain a fully developed embryo, we conclude that they exhibit epicotyl physiological dormancy (PD). Furthermore, we propose that this dormancy represents a new type of epicotyl PD, symbolized by the formula: Ccry(root)-C1bp(shoot), where “cry” depicts the crypto-viviparous nature of the radicle or the hypocotyl.

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