**5. Breeding for drought resistance — Selection environment**

Breeding for drought must be conducted with adequate concern for the selection environment. Adequate care and appropriate consideration must be given to the genotype X environmental interaction during selection of parents and segregants at each filial generation. Ideally, the selection environment(s) must adequately represent the target environment(s) for which the variety/hybrid is being developed. Usually the target environment is highly variable in edaphic, climatic and hydrological status. Every cubic centimeter of soil is different from the other. Aboveground also, the plant faces differences in climatic condition during the day/night, across the season and over year(s). Thus, every cubic centimeter aboveground and below‐ ground is likely to be different and the plant has to adapt to this. If the habitat covers a large geographic area, so as to explain the variability that exists, it is usually referred to as a 'population of habitats'.

Any significant deviation between the selection environment (where the parents and the segregants chosen are evaluated/advanced) and the target population of habitats would make the final selected variety/hybrid inadequately adapted contributing to failure of the crop improvement program. An alternative to having the selection environment geographically isolated or distant from the target environment is to perform selection in the target environ‐ ment itself. The farmers of the target habitat(s) could be involved in the selection process. Such a breeding program, conducted on the farmers' fields (target environments) involving target farmers is referred to as 'participatory plant breeding'.

Unjustifiably it is perceived that breeding for drought resistance is difficult because

**a.** It is a complex trait,

accomplished in spite of this. The argument is amply exemplified by the rapid strides and break-through accomplished in the 1. Semi-dwarfism, 2. Heterosis 3. Development of synthetic varieties of *Triticum aestivum,*L. and 4. Continuous improvements in grain yield and quality parameters across crops over years Table 2. In all cases listed above, one common issue is that the genetic basis is still not 'clear'. While concerted efforts are underway in several crops to discern the mode of action, number of genes governing the trait, the promoters, QTLs, etc.,

Synthetic wheat

**Table 2.** Traits for which genetics has not been discerned but have been subject of continued improvement over

Breeding for drought must be conducted with adequate concern for the selection environment. Adequate care and appropriate consideration must be given to the genotype X environmental interaction during selection of parents and segregants at each filial generation. Ideally, the selection environment(s) must adequately represent the target environment(s) for which the variety/hybrid is being developed. Usually the target environment is highly variable in edaphic, climatic and hydrological status. Every cubic centimeter of soil is different from the other. Aboveground also, the plant faces differences in climatic condition during the day/night, across the season and over year(s). Thus, every cubic centimeter aboveground and below‐ ground is likely to be different and the plant has to adapt to this. If the habitat covers a large geographic area, so as to explain the variability that exists, it is usually referred to as a

Any significant deviation between the selection environment (where the parents and the segregants chosen are evaluated/advanced) and the target population of habitats would make the final selected variety/hybrid inadequately adapted contributing to failure of the crop improvement program. An alternative to having the selection environment geographically isolated or distant from the target environment is to perform selection in the target environ‐ ment itself. The farmers of the target habitat(s) could be involved in the selection process. Such

plant breeders have gone ahead and improved each one of the traits.

1 Grain yield Rice, Wheat, Finger millet, Bajra

2 Heterosis Maize, Sorghum, Cotton, Tomato,

**No. Trait Crop**

4 Synthetics (reconstituted allo-hexaploid

genome)

156 Plant Breeding from Laboratories to Fields

'population of habitats'.

decades.

3 Semi-dwarfism Wheat and Rice

5 Genome diplodization Triticale, Synthetic wheat

**5. Breeding for drought resistance — Selection environment**


This argument is invalid because breeders, over years, have been improving traits and crop plants without adequate knowledge about the genetics of the trait they are breeding for. Four classic examples are given in Table 2. Thus, complexity of a trait or lack of information on the inheritance mechanism of a trait has not bothered breeders much. The innovative selection strategies applied in a well understood environment has yielded results year after year in crop after crop. Thus, while breeding for drought resistance too, not having 'complete' knowledge of inheritance of traits, will not be a deterrent.

With reference to the inability to predict the occurrence of drought and the stage at which it would occur within the cropping duration, it is prudent to build drought resistance to a genotype irrespective of the crops' developmental stage. A plant should be able to face the challenge, posed by low-moisture regime, whenever, should it occur [13].

Genetic variability for traits is harnessed by the breeders in a breeding program. There is ample variation for all traits in the germplasm accessions within a given species and across species that are amenable for use. Selection strategies need to be designed to be able to select for traits especially if it involves destructive sampling (example, root traits). Studying roots in segre‐ gating populations is not as easy as studying shoot traits and grain yield. A plant has to be uprooted to expose roots for analysis. This would kill the plant if it is not already mature. The root traits are ideally studied at peak vegetative stage. At maturity there would be decline in the root traits. Thus innovative selection strategies need to be adapted depending on the mode of propagation, reproduction etc. Traits associated with drought resistance valuated under the stress-full environment manifest lower heritability values making selection an unattractive proposition. This is because of the high G x E interactions. This is manifested by 'crossover interactions' typical of improved and traditional accessions when evaluated in the same study [15, 16]. Any effort to improve the Environment (E) in the experimental site might contribute to improve heritability (H) values. But increase the risk of misrepresenting the target popula‐ tion of environment. Crossover effects are not universal and it is possible to break the trend and select for high productivity under stress and relatively high yields under non-stress habitats too [14, 17].

Two examples where selection for root traits was seamlessly incorporated into the breeding program are discussed below in detail.
