Prinnciples of Pure Line Selection

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  Pure Line Selection   Pure line selection is one of the oldest and most important methods of plant breeding. It is mainly used for the improvement of self-pollinated crops. In agriculture, many crop plants show natural variation in characters such as plant height, maturity, grain size, seed colour, disease resistance, and yield. A plant breeder studies this variation and selects the best plant from the available population. When the selected superior plant is self-pollinated generation after generation, its progeny becomes highly uniform and stable. This uniform and genetically similar group of plants is called a pure line.   The concept of pure line selection has played a major role in the development of improved crop varieties. It helped breeders convert variable local populations into uniform and high-performing varieties. The method is simple, scientific, and economical, so it has remained a fundamental topic in plant breeding courses. For undergraduate stud...
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Leaves of pteridophytes

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Leaves of pteridophytes

Leaves of pteridophytes are variously called phyllidia, fronds, foliage, or simply leaves. When metamorphosed to a leaf-stalk, it refers to a petiole. They exhibit the greatest diversity in size, shape, texture, form, and position. Leaves are primarily for photosynthesis, and many pteridophytic plants produce leaves of more than one kind, commonly termed as dimorphic. The following forms are commonly found among pteridophytes.

1. Elongate. In this case, the leaf is elongated but uniform in width at least for the greater part, the width tapering only towards the apex. The common examples are: Macrothelypteris torresiana, Oleandra wallichii, Pteris longifolia, Polyurhythmopityrhis bifida, and Cephalomanes biswasii.

2. Filiform or capillary. The width of the leaf bears only a very small proportion to its length. The common examples are: Stenochlaena palustris, Thelypteris acuminata, Tectaria braunii, Pteris kinabaluensis, Elaphoglossum pumilum, and Linochelium wallichianum.

3. Cordate. The leaf is heart-shaped, broad, and sub-cordate at the base in the anterior view, or amplexicaul. E.g. Lastreopsis philippinensis, Lastreopsis cuspidata, Dicksonia caput- Medusae, Doodia asilauensis, and Schizonepeta ciliata.

4. Roundish. The leaf is circular or semilunar in outline. E.g. Dryopteris blade, Pteridium aquilinum, Phragmitis communis, and Salvinia natans.

5. Imbricate. Leaves that lie one over another like the tiles in a house, for example: Picea robusta, Pinus longifolia, Pinus caribaea, and Dacrydium diatryx.

6. Reniform. The leaf is kidney-shaped with a large sinus. E.g. Microlepia debilis, Goniophlebium serratum, Goniophlebium hastatum, and Goniophlebium dentatum.

7. Fan-shaped. Leaf is very broad and radiaty flattened like a sheet; truncate with a shallow sinus which seldom exceeds one-fourth of the width of the leaf, for example: Goniophlebium lanceolatum, Goniophlebium matricarioides, Goniophlebium repens, and Goniophlebium tenellum.

8. Stalked. The leaf or frond is borne on a petiole-like or foot-stalk-like structure, for example: Polypodium, Pteris, Nephrolepis, Marattia, and Angiopteris.

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