Title: Discuss plant breeding techniques used in self- pollinated plants v/s those used in cross-pollinated plants?Name: Babooa Anusha
Plant breeding is the art and science of improving the genetic makeup of plants in relation to their economic use for the mankind. Its continuous aim is to improve the quality, diversity and performance of agricultural, horticultural crops. The objective of plant breeding is to develop plant that is better adapted to human needs. Various approaches that are used for the genetic improvement of crop plants are referred to as plant breeding techniques. The choice of breeding techniques mainly depends on the mode of pollination, mode of reproduction, gene action and breeding objective of crop species. A plant breeder tends to divide crop plants species into two groups: self-pollinating plants and cross pollinating plants.In self-pollinating plants, thepollen grains are transferred tothe stigma of the same flower or adifferent flower in the same plant.A self-pollinating plant is capableof fertilizing itself and tends to behighly homozygous because all ofits genes come from the sameparent. Example of self pollinatedplants is Rice, Wheat, Tomato,Okra, Peanut, Potato, etc. Broadly,there is two ways whereby selfpollination can occur.
However, if the pollen grains aretransferred to a flower in anotherplant of the same kind, it is calledcross-pollination.A cross-pollinated plant cannotfertilize by itself and is likely to behighly heterozygous. Thesespecies include corn, rye, alfalfa,clover as well as fruits, nuts andvegetables. Breeding methods for self-pollinating plants are different to some extent from those for cross- pollinating ones. The main breeding methods that will be discussed in this report are as follows: Commonly used methods known as Rarely used methods known as general breeding method special breeding method Plant Introduction Mutation breeding Selection( pureline ;mass selection; progeny) polyploidy Hybridization (pedigree; bulk,single seed Transgenic breeding descent; backcross) Heterosis Recurrent selection, multiline varieties and synthetic varieties are mainly used for crop improvement. 1. Plant introduction It is introducing a plant into new regions from its growing locality. It is the easiest and simplest method. Proper management and acclimatization is very important to prevent losses. Quarantine has to play an important role in introduction to ensure that the material which is to be introduced should not carry pest& diseases with it. It can be used in both self and crossed pollinated plants.
Different geographical regions Different soil type 2. Selection A. Mass selection It is the oldest & easiest method of selection and is useful in self- pollinated species and rarely in cross-pollinated species. It is based on the ability to recognize desirable or undesirable traits in plants of a population. The varieties developed through mass selection are more widely adopted than pure lines though they are not uniform. It takes about 8 years to produce a variety by this method. Steps involves: Eliminating undesirable plants as they are grown in the field (negative mass selection); Tag desirable plants at maturity (positive mass selection); Select best individuals and mix seed.B. Pure line selectionIt is a method in which a new variety isdeveloped by selection of a single best plantprogeny among traditional varieties or landraces. It is applied mostly to self-pollinatedcrops. It is also used sometimes in cross-pollinated species for development of inbredlines. Steps involves: Selection of superiorindividual plants (200-3000 plants); visual
C. Progeny selection It is used extensively in cross-pollinated species. Plant are selected on basis of phenotypic superiority and allowed to open-pollinate. Seeds are harvested separately and progeny rows are grown from the selected plant. This process is repeated till superior families are selected to produce a new variety.3. Hybridization/ Heterosis The mating of two lines of different genotype is known as hybridization. This method is used in both cross & self-pollinated crops. However, it is common in cross-pollinated and rare in self-pollinated species. Out crossing (crossing between genetically different plant) in cross-pollinate crops often results in heterosis/hybrid vigour. Conversely, cross- pollinated plants exhibit inbreeding depression, in the form of small size, poor vigour which is contrary to self-pollinated species that do not exhibit inbreeding depression, but may exhibit considerable heterosis.
Repeated inbreeding Repeated inbreeding Inbred A Inbred B F1 A BA. Pedigree selection It is a widely used method of A B breeding self-pollinated species F1 (and even cross-pollinated species such as crops produced as hybrids). Detailed records of F2 the origin of the selected lines are maintained. It produces new cultivars faster than mass F3 selection. In self-pollinated crop, it is used to release new varieties. In cross-pollinated F4 crops, it is used to develop inbred lines. Fn
B. Bulk method This method can handle segregating generations, in which F2 and subsequent generations are harvested in bulk to grow the next generation. At the end of bulking period, individual plant selection and evaluation is carried out in the similar way as in pedigree method. This method is used in self- pollinated plant species. C. Single seed descentIt is a method used in self-pollinated species. It is a modification ofthe bulk method. Instead of bulking a whole seed lot of selectedplant, a single seed is selected randomly from each selected plant tomake bulk.
C. Backcross breeding Well-adapted cultivarIt conserves all good characteristics of a popularadapted variety and incorporates a desirablecharacter from another variety. A cross between ahybrid and one of its parents is known as backcross.It is applicable to both self and cross-pollinated Cultivar with toospecies. This method is also used for development of many wildmultilines and transfer of male sterility. characteristics New 4. Recurrent selection It can be broadly defined as the selection of desirable plants from a population followed by recombination of the selected plants to form a new variety. It is a refined version of the mass selection procedure and is used mainly in cross-pollinated species. 5. Synthetic and multi line varieties Synthetic varieties are developed in cross-pollinated species. It is produces by crossing in all combination a number of lines that combine well with each other. These varieties have been of great value in the breeding for cross-pollinated crops whereby pollination control is difficult. The maize program CIMMYT places a considerable emphasis on synthetic varieties. Multiline varieties are a mixture of several pure lines of similar phenotype (height, seed color) but have different genes for the character under consideration. These varieties are developed in self-pollinated crops.
5. Mutation breeding Inducing desirable mutations and exploiting them for crop improvement is known as mutation breeding. It is more valuable in self than cross-pollinated crops. It may occur directly during cell division or by exposing the plant to irradiation or chemical agents. 6. Polyploidy Normal cell divisionA cell is a polyploid if it has at leasttwice the normal number ofchromosomes. It can occur spontaneouslyor can be induced using chemicals suchas colchicines. The plants are larger Colchicines 2 diploid diploidcompared to those having normal number dissolves cellsof chromosomes. However, it is rarely spindlesused in both self & cross-pollinated tetraploidcrops. 7. Transgenic breeding It serves to introduce gene sequences for expression of a desired trait. It is applicable to both types of crop species. This method is used to solve specific problems which cannot be solved by conventional breeding techniques.
Plant breeding has several useful applications in the improvement of crop plants. This hasincreased the productivity and quality of the plant we grow for food, feed and fiber. However, ithas certain undesirable effects. Conventional plant breeding can no longer sustain the globaldemand with the increasing population, decline in agricultural resources such as land and water.Thus, new crop improvement technologies should be developed and utilized.References: Principles of plant breeding R.W.WALLARD. December 1960 Agricultural biotechnology, international service for the acquisition of AGRI_BIOTECH application, Aug 2010.pdf Breeding self-pollinated species.pdf FIBL Dossier, plant breeding techniques, No2 September 2001, 1st edition.pdf EAMCET_QR_botany_SR_botany_11 crop improvement .PDF Department of genetics and plant breeding, GBPR 211.pdf