Development of RAPD Markers Associated with Drought Tolerance in Bread Wheat (Triticum aestivum)

Abstract

Wheat (Triticum aestivum) is the most important strategic cereal crop for the majority of the world populations. It is the most important staple food for about two billion people (36% of the world population). It exceeds in acreage and production than other grain crops (including rice, maize, etc.).
Wheat is an edible grain, one of the oldest and most important of the cereal crops in Egypt. The annual consumption of wheat grains in Egypt is about 12.4 million tons, while the annual local production is about 8.52 million tons / 1.32 million hectare in 2008/2009 (The Agricultural Economics and Statistics Department, Ministry of Agriculture, Egypt (2009)). Though grown under a wide range of climates and soils, wheat is the best adapted crop to regions with rainfall between 300 and 900 mm.
World food production is primarily limited by environmental stresses. It is very difficult to find ‘stress free’ areas where crops may approach their potential yield. Abiotic environmental factors are considered to be the main source (71%) of yields reductions (Boyer, 1982). Drought
is one of the most common environmental stresses that affects growth and development of plants through alterations in metabolism and gene expression (Leopold, 1990). Wheat production suffers from variability in yield from one year to another and from location to another. Plant species vary in their sensitivity and response to the decrease in water potential caused by drought, low temperature or high salinity. It could be assumed that all plants have encoded capability gene(s) for stress perception, signaling and response (Bohnert et al., 1995). Drought stress may occur early in the season or terminally at grain filling and development. Productivity improvement of wheat cultivars under drought conditions becomes one of the important objectives in wheat breeding program. Breeding for drought tolerance of wheat cultivars is a major objective in arid and semi-arid regions of the world. due to inadequate precipitation, shortage of water irrigation and high water demand due to crop evapotranspiration in such climates.
Most of the Egyptian newly reclaimed lands (West and East of the Delta and West of the Nile Valley in Upper Egypt) suffers from drought and salinity stresses. Therefore, there is a major need to increase drought tolerance for the Egyptian wheat cultivars to increase the Egyptian wheat production, especially in the new lands, to meet the increasing consumption due to the increasing number of population.
Traditional methods of plant breeding have made a significant contribution to crop improvement such as: targeting complex traits like grain yield, grain quality and abiotic stress. Genetic modifications of crops can be carried out by new techniques such as somaclonal variation, protoplast culture, genetic engineering, in vitro pollination or hybridization, and double haploid production. The evaluation of genetic variations in wheat has been carried out using molecular markers based on RFLPs and RAPDs (Plaschke et al., 1995). Moreover, molecular markers are useful tools to study the genetic variations, since the genetic variability among wheat varieties is narrow as in all self-pollinated crops (Röder et al., 2002). The applications of molecular markers in plant breeding programs facilitate the improvement of many crop species (Williams et al., 1990). The detection of RAPD markers on the genomic map of different field crops is beneficial to improve breeding programs for these crops. It offers the simplest and fastest method for detecting a great number of genomic markers in less period of time (Edwards et al., 1992). Michelmore et al. (1991) developed the F2 plants population to the highest and the lowest extremes for the development of RAPD markers needed for marker-assisted selection. Marker-assisted selection program was progressed by RAPD markers in several crop plants such as rice (Naqvi et al., 1995), wheat (Penner et al., 1996), durum wheat (Wang et al., 1995), rapeseed (Jourdren et al., 1996) and maize (Abdel-Tawab et al., 1998).
The objectives of this study are to screen the responses of twenty bread wheat varieties under drought condition with respect to their performances for some drought-related traits, to select the most tolerant and the most sensitive varieties. Test drought stress on these two contrasting parents and their F1 and F2 plants by recording the previous drought– related traits. Detect some RAPD markers associated with drought stress to be used in marker-assisted selection (MAS) programs.