Peroxidase isozyme characterization of elite genotypes of Pearl millet (Pennisetum glaucum (L.) R. Br)

Isozyme markers are the oldest among molecular markers. Isozyme markers have been successfully used in several crop improvement programmes. Peroxidase (POX) isozyme has proven to be reliable genetic marker in breeding and genetic studies of Pearl millet. The present study was conducted to characterize 21 genotypes (7 hybrids, 6 female parents, 5 male parents and 3 open pollinated varieties (OPV) of Pearl millet by using POX isozyme. Five bands were found with Rm/Rf value ranges from 0.5 to 0.64. All bands were found to be polymorphic in nature except band with Rm value of 0.55 which was present in all genotypes. Intensity of bands varied with each genotype. Only 3 genotypes (H 77/29-2, HMS 7A and HHB 94) out of 21 genotypes were differentiated from other genotypes. Similarity indices based on POX banding pattern revealed that hybrid HHB 50, HHB 60, HHB 67 and HHB 146 completely resembled (SI 1.000) with their female parents MS 81A, MS 843A and ICMA 95222A. This showed the maximum contribution of female parent in comparison with male parent towards the development of hybrid.


INTRODUCTION
Pearl millet (Pennisetum glauccum (L.) R. Br.) provides stable food for millions of people of African countries and Indian sub-continent.It is the sixth important cereal, primarily gown for grain and fodder production.Pearl millet growing in environments in these areas are characterized by low and erratic rainfall, high temperature and poor soil fertility.In these environments, Pearl millet is the only successful cereal and a major source of energy for the poor farming community.With ability to adopt diverse agro-ecological conditions, it plays a unique position in world agriculture.Pearl millet is a summer annual grass originating from Africa, from where it was introduced into other regions of the world with diverse agro-climatic conditions, that is, from the hot area of Africa to the hot area of temperate zones.Therefore, a large number of diversity is found within and among pearl millet cultivars.Due to its highly out-crossing breeding behaviour, Pearl millet was originated from several independent domestication events and wide range of stressful environmental conditions, in which it had been traditionally cultivated.Pearl millet exhibits a tremendous amount of diversity at both phenotypic and genotypic levels (Poncet et al., 1998;Liu et al., 1994).
Estimation of genetic diversity and identification of superior genotypes are some of the prime objectives of any crop improvement programmes.Highly diverse genotypes or accessions can be utilized as parents in hybridization programmes to produce superior varieties/hybrids.Therefore, there is a need to evaluate available genotypes for their genetic diversity.In the early *Corresponding author.E mail: mani.vannan.461@gmail.com.Tel: +91 8940080450.
days, crop breeders used morphological markers for the assessment of genetic diversity and choosing parents for developing new cultivars.Morphological markers data are affected by the interaction of the genotype with the environment in which it is expressed.Moreover, due to the high out-crossing breeding nature and structure of genetic diversity in pearl millet species, the morphological data/markers are inadequate in providing reliable information for the calculation of genetic distance and pedigree studies.
Isozyme markers are the oldest among the molecular markers.Isozyme markers have been successfully used in several crop improvement programmes (Glaszmann et al., 1989;Baes and Custsem, 1993).Isozymes have proven to be reliable genetic markers in breeding and genetic studies of plant species (Heinz, 1987), due to consistency in their expression, irrespective of environmental factors.Isozymes provide useful evidences in the study of variation between cultivars in terms of intensity of common bands and presence or absences of other bands (William and Mujeeb, 1992).Study of the isozyme pattern is considered as an important tool for understanding the genetic relationship between individuals and also for the identification of hybrids.Genetically, the production of isozyme of multiple forms or molecular weight is accounted to the allelic variation of the organism.Therefore, isozymes of a particular molecular weight can be considered as a direct manifestation of the blue print of the specific gene loci (Abiden and Vijayakumar, 2002).The utility of isozymes as genetic marker (Cheniany, 2007) is generally attributed to their polymorphism, codominence, simple inheritance, simple assay and obliquity in plant tissues or organs (Simpson and Withers, 1986).Moreover, isozymes study may be useful to diversity analysis in plants (Philomina and Surendran, 2003).Peroxidase (POX) isozyme has been widely used for characterization of plant germplasm (Li and Li, 1996;Ju-Zheng et al., 1997;Gupta et al., 2008).An attempt was made to study the isozyme diversity in some of elite Pearl millet varieties, hybrids and their parental lines.1).

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To record the electrophoregram of POX, the method followed was that of Mitra et al. (1970).The POX was displayed as brown bands.Based on polyacrylamide gel, bands were scored as present {1} and absent {0} in data sheet to form a {1, 0} matrix.Then data were analyzed and similarity matrix was constructed from binary data with Jaccard's coefficient (Jaccard, 1908) and dendrogram were generated with Unweighted Pair Group Method Arithmetic Average (UPGMA) algorithm using NTSYSPC -version 2.01 software (Rohlf, 2000).

Table 1 .
List of Pearl millet genotypes and their pedigree.

Table 2 .
Banding pattern of POX isozyme in 21 genotypes of pearl millet.

Table 3 .
Schematic zymogram of POX isozyme in 21 genotypes of pearl millet.

Table 4 .
Similarity indices between hybrid and their parents.