Glossary Plant Breeding

AB–QTL Method (Tanksley and Nelson 1996). Advanced Backcross QTL Method. It is
a method for simultaneous discovery and transfer of valuable QTLs from unadapted
germplasm into elite breeding lines. It involves use of BC 2 /BC 3 (or their self or test
cross progenies) for phenotyping and genotyping using molecular markers. Such
populations are non-random resulting from intense selection in BC 1 /BC 2 and allow to
identify yield and yield component QTLs. Using this method, two wild QTL alleles
namely, Yld 1.1 and Yld 2.1 from O. rufipogon (using ‘RM5’ and ‘RG256’ markers,
respectively) have been identified and introgressed into cultivated hybrid rice. Each of
the two has been shown to confer yield advantage of more than 18% in the hybrid
rice. IthasbeenalsousedtoidentifysuchgenesinLycopersicon prempenellifolium.
One of the main demerits of this method is that BC 2 /BC 3 populations are effective for
detecting dominant and overdominant QTLs only; recessive QTLs go undetected.
Acaryotic. Referring to a cell without nucleus.
Accessory Chromosomes. Sex chromosomes and other supernumerary chromosomes
such as B-chromosomes.
AChromosome.Any member of the normal chromosome complement in contrast to the
B-chromosomes.
ALine. The male-sterile parent line to produce hybrid seed. It is the seed-producing line,
always used as the female parent. It has ‘sterile’ cytoplasm and recessive nuclear
gene(s).
A Posteriori. Derived by reasoning from observed facts (data).
APriori.Based on hypothesis or theory rather than on experiments or experience.
Abiotic Stress. Any kind of abnormal condition due to non-living components of
environment (high or low temperature and moisture, high salinity or acidity in soil,
forexample)thatadverselyaffectsgrowthand reproduction of crop plants. Breeding
for abiotic stress is considered more difficult because of: (a) complexity of conditions
causing abiotic stresses, (b) complex nature of abiotic resistance in a variety, (c)
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