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Marker-assisted selection and gene pyramiding are very important breeding strategies for conferring broad spectrum and durable resistance against diseases causing yield loss in rice. One such disease causing major set backs in rice production is bacterial leaf blight (BLB) caused by the pathogen Xanthomonas oryzae pv. oryzae. Molecular markers are very essential in both marker-assisted selection and pyramiding of genes, hence, many molecular marker techniques have already been developed. Presently, the most commonly used ones are DNA-based markers also known as molecular markers. The molecular markers are classified into two major categories based on the techniques used for detecting them. These are hybridization and polymerase chain reaction-based markers. Other types of markers available include the morphological (traditionally based) and biochemical (enzyme-based) markers. Host plant/varietal resistance is the most suitable means for controlling BLB disease of rice. Marker-assisted gene pyramiding has the potential to accelerate the breeding programmes and guarantee the durability of resistance conferred in the host plant. Therefore, this paper uncovers the utilization, economic importance, limitations and future prospects of marker-assisted selection and gene pyramiding for resistance to BLB disease of rice.

This research was conducted at the teaching and research farm of the Department of Crop Production and Landscape Management, Ebonyi State University, Abakaliki, from 2006 to 2012 cropping seasons to develop maize populations of increase protein, oil, amylose and amylopectin contents. Total of eight (8) maize varieties were used for the study and were grouped into two populations, A and B. Population A was coded A 1 , A 2 , A 3 and A 4 while population B was coded B 1 , B 2 , B 3 and B 4 . These two populations were genetically variable based on the time of maturity, percentage protein, oil, amylose and amylopectin. The mean protein content of the parents was 8.74% while their progenies after second cycle had percentage protein content of 13.27%, showing an increase of 4.53% with mid parent heterosis of 52%. The oil content of the open-pollinated maize varieties was pushed towards increasing order from 6.19% for population A and 4.19% for population B of the original populations to 5.61% and 5.62% for populations A and B respectively of the first cycle populations. These were further pushed up to 8.08% and 8.46% of the second cycle populations A and B respectively. The mean amylose content of the original population was 24.25% and the mean amylose content of the progenies after the first cycle was 22.02%. The second cycle synthetics had mean amylose content of 19.72%, showing a decrease of 4.53%. The mid parent heterosis was -9.2%. The mean amylopectin content of the original population was 75.75% and the mean amylopectin content of the selected high amylopectin was 82.13%, showing an increase of 6.38% over the mean amylopectin content of the original population. The breeding programme seems to be very effective in improving both the high, medium and low protein, oil, amylose and amylopectin contents of the original maize populations to all high protein, oil and amylopectin contents, except amylose, after the second cycle. In all, this method offers definite promise. Further progress in improving chemical constituents as well as other characters is theoretically possible in future cycles.