**6. Breeding for drought resistance — Marker-assisted selection**

Marker-assisted selection is expected to boost the pace of crop improvement especially for complex traits. This was the feeling of molecular biologists who want about discovering DNA markers in large numbers. Overtime, the markers have evolved. There is always a search for ideal markers which can be used by breeders. Characteristics of ideal markers are as follows


The first QTL tagging work, for root traits was done by IRRI, Philippines in 1995 [18]. Ever since a very large number of QTLs have been discovered for every component trait expected to contribute to drought in several crops. Each one of them, proposed that the QTLs discovered would help MAS for drought. A large number of QTLs associated with traits related to drought have been tagged to different kinds of molecular markers [13, 19]

So far, the only documented success stress with MAS for root traits has been the work of [20] in rice. In this paper too, out of the five loci selected for MAS, only one locus of chromosome 9 had a significant and positive effect on root traits. Phenotyping done among the transgres‐ sants aided in the selection process.

A novel upland rice variety, BirsaVikasDhan 111 (PY 84), has recently been released in the Indian state of Jharkhand. It was bred using marker-assisted backcrossing with selection for multiple quantitative trait loci (QTL) for improved root growth to improve its performance under drought conditions. It is an early maturing, drought tolerant and high yielding variety with good grain quality suitable for the direct seeded uplands and transplanted medium lands of Eastern India. PY84 is the first example of a rice variety bred through the combined use of marker-assisted selection and client-oriented breeding, and a rare success story for the use of marker-assisted selection to improve a quantitative trait. It out-yields the recurrent parent by 10% under rain fed conditions. The variety was developed in a collaborative partnership between CAZS-NR; GraminVikas Trust, Ranchi, Jharkhand, India and Birsa Agricultural University (BAU), Ranchi, Jharkhand, India. The target QTL was first identified by Adam Price (Aberdeen University, UK) and Brigitte Courtois (CIRAD, France/IRRI, Philippines) [20].

In this marker assisted backcrossing program (MABC) was used. The strategy was to pyramid different QTLs situated on different chromosomes. All these QTLs were related to root traits. An Indian *indica* rice variety was used as the recurrent parent. The donor for deep-rooting and grain aroma was Azucena, a *japonica* from Philippines. Five segments on different chromo‐ somes were targeted for introgression; four segments carried QTLs for improved root mor‐ phological traits (root length and thickness) and the fifth carried a recessive QTL for aroma. Twenty-two near-isogenic lines (NILs) were evaluated for root traits in five field experiments in Bangalore, India by Dr. H.E. Shashidhar. The target segment on chromosome 9 (RM242- RM201) significantly increased root length under both irrigated and drought stress treatments, confirming that this root length QTL from Azucena functions in a novel genetic background. No significant effects on root length were found at the other four targets. Azucena alleles at the locus RM248 (below the target root QTL on chromosome 7) delayed flowering. Selection for the recurrent parent allele at this locus produced early-flowering NILs that were suited for upland environments in eastern India (Figure 2).

**Figure 2.** A flow chart for MAS for drought resistance.

**6. Breeding for drought resistance — Marker-assisted selection**

groups (polygenic trait)

sants aided in the selection process.

allelic combination

158 Plant Breeding from Laboratories to Fields

interest.

Marker-assisted selection is expected to boost the pace of crop improvement especially for complex traits. This was the feeling of molecular biologists who want about discovering DNA markers in large numbers. Overtime, the markers have evolved. There is always a search for ideal markers which can be used by breeders. Characteristics of ideal markers are as follows **1.** Tightly linked to gene that controls the trait either individually (monogenic trait) or in

**2.** Co-dominant in inheritance. It will help identify heterozygotes and homozygotes with ease. Dominant markers are also useful but they identify only one of the homozygous

**3.** PCR based so that it can be analyzed faster. It would be better if the amplified bands could

**4.** The marker should account for a large proportion of the genetic variability for the trait of

The first QTL tagging work, for root traits was done by IRRI, Philippines in 1995 [18]. Ever since a very large number of QTLs have been discovered for every component trait expected to contribute to drought in several crops. Each one of them, proposed that the QTLs discovered would help MAS for drought. A large number of QTLs associated with traits related to drought

So far, the only documented success stress with MAS for root traits has been the work of [20] in rice. In this paper too, out of the five loci selected for MAS, only one locus of chromosome 9 had a significant and positive effect on root traits. Phenotyping done among the transgres‐

A novel upland rice variety, BirsaVikasDhan 111 (PY 84), has recently been released in the Indian state of Jharkhand. It was bred using marker-assisted backcrossing with selection for multiple quantitative trait loci (QTL) for improved root growth to improve its performance under drought conditions. It is an early maturing, drought tolerant and high yielding variety with good grain quality suitable for the direct seeded uplands and transplanted medium lands of Eastern India. PY84 is the first example of a rice variety bred through the combined use of marker-assisted selection and client-oriented breeding, and a rare success story for the use of marker-assisted selection to improve a quantitative trait. It out-yields the recurrent parent by 10% under rain fed conditions. The variety was developed in a collaborative partnership between CAZS-NR; GraminVikas Trust, Ranchi, Jharkhand, India and Birsa Agricultural University (BAU), Ranchi, Jharkhand, India. The target QTL was first identified by Adam Price (Aberdeen University, UK) and Brigitte Courtois (CIRAD, France/IRRI, Philippines) [20].

In this marker assisted backcrossing program (MABC) was used. The strategy was to pyramid different QTLs situated on different chromosomes. All these QTLs were related to root traits.

**5.** The marker must be able to identify all other allelic forms associated with the trait.

be resolved on agarose gels or data acquired as quickly as possible.

have been tagged to different kinds of molecular markers [13, 19]
