Effect of presowing seed treatments on teak (Tectona grandis L. F) drupes dormancy and germination

Poor seed germination is a major issue in teak (Tectona grandis) propagation. Teak seed dormancy is thought to be the reason for delayed germination. So far, specific dormancy mechanisms have not yet been identified. In order to study the influence of presowing treatments on germination, seedling vigour, and biochemical attributes of fresh teak drupes collected from the seed production area of Top Slip in Tamil Nadu. The collected drupes were subjected to different presowing treatments viz., T1 - control, T2 - soaking and drying for 6 days, T3 – T18 (soaking and drying for 5 days + soaking in different concentrations of thiourea, potassium nitrate,  hydrogen peroxide and calcium oxychloride for 12 hours). Treated drupes were placed for germination in earthen pots and kept in open sunlight. In parallel, true seeds extracted from untreated drupes were also subjected to germination under in vitro conditions as a check. A higher percentage of germination (40%) was recorded in true seeds under in vitro conditions when compared to the treated and untreated drupes under in vivo conditions. Among the treated drupes sown under in vivo conditions, the drupes given soaking + drying for 5 days + soaking in 2% calcium oxychloride (CaOCl2) recorded higher germination (17.16) with better seedling vigour. Analysis of teak true seeds and mesocarp extract in high-performance liquid chromatography showed that gibberellic acid was found only in true seeds, whereas the other compounds, viz., indole-3-acetic acid, indole butyric acid, abscisic acid and coumarin, were not present in the true seed or mesocarp

Impact of the orientation of seed placement and depth of its sowing on germination: A review

Seed orientation and its impacts on germination and seedling establishment mainly depend on the type of germination (hypogeal (or) epigeal), seed size and shape. Higher germination per cent is noticed when seeds are sown in the horizontal position. Planting seeds in a downward position can lead to a variety of physiological, chemical and morphological changes in seedlings. Consequences are usually manifested as noticeable modifications in their development. Vigorous seeds have strong, resilient seedlings due to their well-balanced metabolism and coordinated subcellular activity, making them well-suited for tough environments. Proper plumule and radicle growth require additional hormones and energy to ensure seedling survival. Four necessary factors must be considered while deciding the sowing depth viz., soil moisture, optimum soil temperature, soil aeration and atmospheric humidity required for seed germination, emergence and seedling growth. Variations are observed in germination behaviour and seedling growth for different sowing depths. The necessary factors are very much important for efficient nursery seedlings production. This review looks at the effects of seed depth and orientation on the germination and growth of important agricultural, horticultural and silvicultural crops

Effect of ageing on in vitro true seed and in vivo drupe germination and its dormancy mechanism in teak (Tectona grandis Linn.f)

The germination percentage of teak seed is generally very poor due to its higher percentage of empty seed and poor seed viability. The viable seeds exhibit protracted germination behaviour due to their inherent seed dormancy and other physiochemical characteristics. Hence establishing a teak nursery for largescale plantation activities is a challenging task. This study was undertaken to study the effect of ageing on in vitro true seed and in vivo drupe germination and its dormancy mechanism in teak. Fresh, one-year and two-year stored drupes were used to represent different levels of ageing. Under in vivo conditions, poor drupe germination was observed in fresh drupes (3%) and germination percentage was increased when the drupes were subjected to ageing for one year (17%) or two years (32%). When true seeds separated from fresh drupes and germinated under in vitro conditions, enhanced germination (58.3%) was observed. Biochemical analysis showed that indole-3- acetic acid, indole butyric acid, abscisic acid and coumarin are not present in fresh, one year and two-year-old true seeds. The gibberellic acid was increased with an increase in ageing, but the GA3 did not influence the germination percent under in vitro conditions. Scanning electron microscope (SEM) image of fresh teak true seed showed that embryo tip was shrivelled, whereas one and two-year-old true seed embryo tip bulged; this was confirmed that one and two-year-old true seed embryos were matured and satisfied the after-ripening requirement. Nursery studies revealed that one and two-year-old drupes recorded the highest germination compared to fresh drupes.