“Alternative experimental designs for plant breeding”

UNIVERSITY OF AGRICULTURAL SCIENCES, BANGALORE

Department of Genetics and Plant Breeding

Seminar - GPB 681 (0+1)

“Alternative experimental designs for plant breeding”

Crop improvement is a continuous process and development of new cultivars better than the existing ones is the ultimate objective of plant breeding. In order to meet this objective, plant breeders regularly generate experimental materials and evaluate them in an experimental design with elite cultivars termed as checks. The choice of the experimental design depends critically on the number of entries being evaluated and availability of seeds for replications. Experimental design is the process of carrying out research in an objective and controlled fashion so that precision is maximized and specific conclusions can be drawn regarding a hypothesis statement.

Deciding an experimental design requires familiarity with the benefits and drawbacks of each option, as well as the levels of variation seen in experimental fields and breeding program germplasm. Simpler designs like Complete Randomized Design (CRD) and Randomized Complete Block Designs (RCBD) are easy to implement and analyse when the number of genotypes is less. But breeders deal with large number of populations like recombinant inbred lines, back cross inbred lines, and germplasm lines etc., based on the objectives. Evaluation of such populations with more than twenty entries utilizing CRD or RCBD reduces the precision of the experiment. Hence, there is a need to replace these designs with alternative designs wherein it reduces the soil heterogeneity which in turn reduces the error sum of squares.

Incomplete Block Designs (IBD) are designs with block size less than the number of treatments to be tested. These designs were introduced by Yates in order to eliminate heterogeneity to a greater extent than is possible with randomized blocks. When the number of replications of all pairs of treatments in a design is same, then the class of IBD is called Balanced Incomplete Block (BIB) designs and when there are unequal number of replications for different pair of treatments, then the designs are called Partially Balanced Incomplete Block (PBIB) designs. PIBD includes lattice design (Square, Rectangle, Alpha) which needs less number of replications and also it is resolvable to complete replication.

Latin square designs are a class of designs which include two-way elimination of heterogeneity. The most common ones used are row-column and Youden square with equal number of rows, columns, and treatments. Breeders encounter situations where they cannot replicate the genotype because of scarcity of seeds or large number of lines to be evaluated. In such cases, augmented design could be used where only the checks are replicated and the entries are not replicated.

A large number of germplasm and segregating population of wheat were evaluated to compare the efficiency of RCBD and Alpha Lattice Design (ALD). Nine drought tolerance indices were subjected to analysis of variances of both the designs ALD and RCBD. The relative efficiency of trials shows that ALD was more efficient than RCBD design. Based on grain yield per plant under both the conditions twenty-one tolerant genotypes and eleven susceptible genotypes were identified.

Breeders frequently conduct field trials where the objective is to select the best entries. After the entries to be compared have been identified, the breeder will seek the best design and method of analysis. The selection of design should be such that the error component should be reduced to minimum.

References:

1. Kumar, A., Bharti, B., Kumar, J., Bhatia, D., Singh, G. P., Jaiswal, J. P. and Prasad, R., 2020, Improving the efficiency of wheat breeding experiments using alpha lattice design over randomized complete block design. Cereal Res. Commun., 48: 95-101.

2. Singh, P. and Bhatia, D., 2017, Incomplete block designs for plant breeding experiments. Agric. Res. J., 54(4): 607-611.

3. Zystro, J., Colley, M. and Dawson, J., 2018, Alternative experimental designs for plant breeding. Plant Breeding Reviews, 42: 87-117.