INTRODUCTION TO PLANT BREEDING

AGRONOMY 815 / COURSE NOTES

P. STEPHEN BAENZIGER, 338 Keim Hall, 472-1538

DEPARTMENT OF AGRONOMY / UNIVERSITY OF NEBRASKA

BREEDING PROCEDURES PRIMARILY
UTILIZED IN CROSS-POLLINATED CROPS

Fehr, Chapt. 12, 15
Briggs and Knowles, Chapt. 19.

Originally, an improved version of the open pollinated variety was the ultimate objective. Today, extraction of elite inbred lines that can be combined to give superior hybrids or intercrossed to form elite synthetics, may be the final goal.

The improvement of source populations via the accumulation of desirable alleles through some form of recurrent selection is an important part of a breeding program.

With better understanding of genetic effects governing characters of economic importance and how the genotype interacts with the environment, a number of recurrent selection methods have been developed.

The earliest breeding procedure used in plant improvement was mass selection. In naturally crossed pollinated species, mass selection is actually a form of recurrent selection.

RECURRENT SELECTION -- Selection of plants with superior phenotypes in the breeding population and the intermating of these selected individuals to form the new population.

Selection may be based on the phenotype of the individual itself (mass selection) or on the mean phenotype of its family.

Recurrent selection methods can be divided into two categories:

  1. Intrapopulation improvement . . . tends to maximize improvement of the population itself and the inbred lines derived from it;


  2. Interpopulation improvement . . . maximizes improvement in the population cross and hybrids between the lines from the two different populations involved.


INTRAPOPULATION METHODS

MASS SELECTION

  1. Selection based on the phenotype of the individual.


2 Methods: 1. Selection made prior to pollination.

• Only selected individuals are intercrossed. Hand pollinate or eliminate undesirable plants. Has greater genetic gain because control both parents.

2. Selection made after pollination.

• Seed parent selected at harvest, pollen random. Isolation needed to avoid contamination.

One cycle (generation) of improvement per year. Select and recombine or vice versa.

With Mass Selection -- minimize environmental variation as much as possible; e.g., minimize unequal competition effects . . . overplant and thin to a perfect stand. Avoid stress. Use grid system of selection.

The effectiveness of mass selection is dependent upon the accuracy with which the phenotype reflects the genotype. In corn, characters such as maturity, plant height, ear size and oil content were amenable to improvement via mass selection; however, yield, with its low heritability, was less responsive to mass selection until the need for better control of environmental variation was realized. (Gardner, 1961. Crop Sci.1:241-245. Yield increase of approx. 3% per cycle in corn using a grid system of selection.)

Mass selection has been a useful method of improvement in many crop species . . . corn, forages, etc. including some self pollinated crops e.g., Tobacco -- yield gain of 4.29% per cycle during the first 4 cycles of mass selection. (Matzinger & Wernsman, 1968. Crop Sci. 8:239-243.)

Mass selection offers considerable potential with relatively small investment.