Introduction of Pests and diseases
Potato tuber moth from Italy; Wooly aphids of apple and fluted scales of citrus from Australia.
· False smut of Wheat – Australia; Coffee rust and Bunchy top of banana – Sri Lanka.
· Adoptation of a variety to a new environment is knows as “acclimatization”.
· All dwarf wheat varieties are derived from crosses with “Mexican dwarf wheat”.
· The gradual loss of variability in the cultivated forms and in their wild relatives is referred to a “Genetic erosion”.
· Gene santuries – May be defined as an area of diversity protected from interference from man.
· “Exploration” are trips for the purpose of collection of various forms of crop plants and their related species.
· The fundamental steps of any breeding programme, are
1. Creation of variation
· The two basic requirements of selection to operate are
1. Variation must be present in the population.
2. The variation must be heritable.
· The ratio of genetic variance to the total variance i.e., phenotypic variance is known as “heritability”.
· “Genetic advance” is the difference between the mean of the progeny and mean of the population from which selection is made.
· Evaluation of the worth of the plants on the basis of performance of their progenies is known as “Progeny test”.
· A pure line is a progeny of a single homozygous plant of self pollinated species.
· Homozygocity % = (2m-1)n/2m
m = No. of generations of selfing.
n = no. of genes segregating.
· Mating (or) crossing of two genetically dissimilar plants is known as “Hybridization”.
· The pedigree may be defined as description of the ancestors of an individual and it generally goes back to some distant ancestors.
· Isogenic lines – Which are identical in their genotype, except for one gene.
· The back cross is the only method for “inter specific gene transfer”.
· Heterosis may be defined as the superiority of F1 hybrid over both the parents.
· Maize is the crop studied against heterosis and inbreeding depression.
· If the F1 is superior over the better parent, it is known as “Heterobeltosis”.
Heterosis = [F1 – ((P1 + P2)/2)]
· Mating between closely related individuals (or) self fertilization is known as “inbreeding”. Loss of vigour and fertility due to inbreeding is known as “inbreeding depression”.
· Top cross: A cross between an inbred and an open pollinated variety.
· Homozygous balance is characterized by lack of inbreeding depression.
· Test cross: When the top cross is made to assess the combining ability of an inbred the cross is called as “test cross”.
· Poly cross: Progeny of a line produced through random pollination by a number of selected lines.
· Varietal cross (or) population cross: A cross between two open pollinated varieties.
· If ‘n’ lines are to be tested in all possible single cross combinations there would be n (n-1) / 2 single crosses without reciprocals and if reciprocals are also included it would be n (n-1).
· The concept of combining ability was proposed by Sprague and Tatum.
· The ability of an inbred to transmit the desirable character to its hybrid progenies in combination with another inbred line is known as “combining ability”.
· The average performance of inbred in series of hybrid combinations is known as its “General combining ability”. This is obtained by “top cross test”.
· Specific combining ability: is a deviation from performance predicted on the basis of GCA estimated by “Diallel crossing”
· Heterosis is mainly due to SCA.
· Number of double cross combinations – n(n-1)(n-2)(n-3)/8.
· Synthetics are important in cross pollinated crops.
· A “Synthetic” may be defined as an advanced generation of open pollinated seed mixture of a number of inbred lines among them.
· Synthetics only exploit GCA; but hybrids exploit both GCA and SCA.
· Syn2 = Syn1 – (Syn1 – Syn0)/n.
n = no. of parental lines.
· A “Composite” variety is produced by mixing seeds of several phenotypically outstanding lines and allowing them to open pollinate in all possible combinations.
· Germplasm complexes are produced by mixing seed from several lines (or) populations of diverse genetic origin.
· Recurrent selection: Method which involves “reselection” generation after generation with interbreeding of selects to provide genetic recombination”.
· In recurrent selection for GCA tester is “open pollinated variety” (broad genetic base).
· In recurrent selection for SCA tester is an “inbred”. (narrow genetic base).
· If dominance is in complete, Recurrent selection for GCA & reciprocal recurrent selection are equal but both are superior to R.S for SCA.
If dominance is complete three methods are equal. If over dominance is present, Reciprocal recurrent selection and recurrent selection and recurrent selection and recurrent selection for SCA both equally superior to recurrent selection and recurrent selection for GCA.
· Male sterility is the condition in which non functional pollen grains are produced.
· The male sterile line may be maintained by crossing it to a heterozygous male fertile. Genetic male sterility is governed by a single recessive gene
· Male sterile Srr X male fertile Frr–> Male sterile Srr.
· Maintainer line is recessive fertile – Frr.
· Incompatability : Heteromorphic – accompany florel. Morphological differences.
Homomorphic : do not accompany any floral morphological differences.
· Long styles, Short stamens – pin type flowers .
Short styles, long stamens – Thrum type.
· In gametophytic incomparability incompatable reaction depends upon the genetic constitution of the pollen itself.
· Fully incompatable – S1S2 X S1S2
Partial compatable – S1S2 X S2S3.
Fully compatable – S1S2 X S3S4.
· By each generation of selfing in Cross Pollinated crops the homozygosity is increased by 50%, while heterozygocity reduced by 50%.
· Term ‘Heterosis’ was coined by “Shull”.
· An auto tetraploid which contains all recessive alleles is termed as “Nulliplex”.
· A “Clone” is a group of plants produced through asexual reproduction from a single plant.
· A sexually propagated crops are invariably cross pollinated.
· Pathogenicity – Ability of a pathogen to infect a host strain.
· Virulence – Capacity of a pathogen to incite a disease.
· When the host does not show the symptoms of disease it is known as “Immune reaction”.
· Phytoalexins are produced by a host in response to infection of the pathogen.
Phytoalexins are either “fungicidal (or) fungistatic”.
· Oligogenic resistance is synonymous to “vertical resistance” (resistance to only one race).
· Vertifolia effect: Epidemic development in “Ono” variety carrying vertical resistance genes.
· In horizontal resistance reproduction rate is not zero but it is less than one.
· Pedigree method is quite suitable for horizontal resistance.
· All three (Yellow, Black & Brown) rusts resistant wheat variety – sparrow.
· Oligophagy – live on one taxonomical unit only. Eg: Hesisan fly (flessian fly).
Seasonal oligophagy – Insects may live on many sps. In one part of the year and on few
in another part of the year. Eg. Aphids.
· The deterimental effect of the plant on the biology of the insect is known as “Antibiosis”.
· Leafhopper resistance – Vijaya (in rice).
· Accumulation of proline (amino acid) content in drought resistance.
· Screening tests are normally conducted in F3 generations of segregating material.
· First induced mutation variety – Charina – F (tobacco).
· Induced mutations commonly pleiotropy often due to mutations in closely linked genes.
· Gene mutations – gamma rays.
· Alpha rays – Chromosomal aberrations, Beta rays, X – Rays Chromosomal and gene mutations.
· Non – ionizing agents use is confined to ‘pollen grains’.
· Polyploids contain generally low dry matter content than diploids.
· Mainly allopolyploids are “Apomictic”.