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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Affinity of Gymnosperms with Pteridophytes

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Affinity of Gymnosperms with Pteridophytes : 

The gymnosperms resemble the pteridophytes by the following features :


(1) Both possess independent sporophytes which are differentiated into root , stem and leaves . Both the groups exhibit heterosporous life cycle .

(2) The sporophytes possess a well developed vascular system such as xylem and phloem . The xylem in most of the members of groups lacks vessels and the phloem lacks companion cells .

(3) Many Cycads resemble the ferns in possesing large compound leaves and the in the circinate ptyxis of the leaves . Dichotomous venation in Ginkgo and ferns .

(4) The female sex organs are archegonia in both the groups .

(5) The male gametes of Cycads and Ginko are motile , like the pteridophytes . 

(6) Many pteridophytes like Marselia,Salvinia , Azolla, Isoetes and Selaginella are heterosporous like the gymnosperms .


( 7 ) Some of the heterosporous pteridophytes possess one megaspore in the megasporangium , like the gymnosperms .

( 8 ) The gametophytes of gymnosperms and heterosporous pteridophytes are endosporic .

(9) In both , the gametophytes are highly reduced and they are developed within the spore wall in some pteridophytes . The male gametophytes of heterosporous pteridophytes and majority of gymnosperms possess only two male prothallial cells .

(10) The female prothallus develops before fertilization and there is free nuclear division .

( 11 ) Development of a distinct embryo after fertilization . The embryogeny is endoscopic in many pteridophytes and all gymnosperms .

( 12 ) Germination of spores is precocious in gymnosperms and heterosporous pteridophytes . 

( 13 ) In the life-history, both sporophytic and gametophytic generations alternate regularly with each other .










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