Determination of viability and number of seeds in smooth narra (Pterocarpus indicus Willd.) fruits by x-ray radiographic technique [Philippines]

An embryo cotyledon classification scheme which is used to judge seed germinability by x-rays was developed by employing the actual germination and x-ray photography methods side by side. Four seed types were categorized namely: (1) Type 1 seed which is the most viable, producing normal seedlings. The radiographs clearly show the usual elongated ellipse shape of the embryo bounded by a narrow cavity. The cotyledons project a similar distinct image, fills the whole seed space completely and reveal strong connection with the hypocotyl; (2) Type 2 seed which is the deteriorating seed that usually produces abnormal seedlings. The x-ray photographs of these seeds reveal gradual diminishing of embryo-cotyledon features. Part of the embryo may not be cle2048arly recognized and the development of an enlarged embryonic and seed cavity is manifested; (3) Type 3 seed which is the damaged or dead seed. The radicle-hypocotyl axis is usually not discernible from the radiographs. Furthermore, cotyledons have shrunk considerably and are likewise indistinct. Evidence of cracks and fissures are readily seen especially in the cotyledonary area and; (4) Type 4 which is the empty or immature seed. The resulting radiograph exhibits diminutive or missing embryo and/or cotyledons. Comparison of viability estimates between x-ray test and direct germination method reveals a high correlation of 0.90 for fourteen sets of seed samples. Determination of the number of seed is greatly facilitated by the x-ray method. Judging the viability of seeds while inside the Samara is extremely difficult due to the artifacts created by the woody veins in the seed containing structure of the samara. The soft x-rays employed has no apparent radio-biological effects both to the seeds in terms of final percent germination and subsequent seedling growth, and to the x-ray operator. A film containing approximately 250 seeds or seeds of its equivalent size may roughly cost P11