Applied Genetics (plant breeding). STB 421 (FOURTH LECTURE)
Plant breeding as an Art and Science
Science: plant breeding dependent on genetic principles. Initially genetics focus on genes with large effects i.e. qualitative characters e.g. colour. Recently on gene with small effect-quantitative character e.g. yield.
Malthius 1798 predicted farming in Britain in the mid - 19th century. The prediction failed because it is an underestimation of man's ingenuity in increasing agricultural production.
Aims of plant breeding
Plant breeding aims at the following:
1. Increaing productivity: e.g. mexico in 1943 imported wheat but with the devotion of scientist she became self surficient in 1956, while in 1965 she became an exporter of wheat. The sugar content of sugar beat was just 7% but with breeding effort it is now over 15%.
2. Expansion in the area of production: example, early maturity, draught resistance and winter hardiness in some cereal crops.
3. Hybrid varieties: example, hybrid corn in the U.S, 95% of corn grown are hybrids.
4. Disease and insect resistance: e.g. wheat steam grost, leave rust in maize (Helminthosporium sp). Disease can lead to crop failure.
5. Quality: e.g. cotton-finess, strength and smoothness of fibres in vegetables e.g. tomato breeders aim to increase vitamin and protein content. Cowpea new variety turns black while cooking.
6. Adaptability to mechanical harvest: e.g. sorghum - dwarf varieties makes it possible for combined harvesters to be used.
Developed varieties have also been found to utilize added import of production better than non-developed varieties. Breeding is however a long term undertaking, it takes at least 10years for an improved variety to be obtained.
Qualities of a plant-Breeder
1. Knowledge of genetic and cytogenetic principles.
2. Knowledge of crop to be improved and its wild relatives.
3. Knowledge of the need of the crop grower.
4. Knowledge of techniques for solving a particular problem.
5. Knowledge of the principle of field plot techniques.
Plant breeding emphases of agricultural productivity through development of crops.
Crop improvement
Crop improvement include breeding, integrated pest and disease management, fertilizer management, spatial arrangement e.t.c.