By ROBERT PLAK and RAKESH KAPILA
PNG is rich in genetic resources, which include cultivated varieties, landraces, genetic stock, wild and weedy species, trees and shrubs. These resources provide much needed foundation and unique opportunities not only for improving their productivity but also for creating more desired diversity and alternative uses. However, without the application of some aspects of biotechnology, it is not possible to explore the opportunities and derive such potentially available benefits. Below are some potential uses and applications.
Characterisation and conservation of PGR
Conservation and sustainable use of crop plant genetic resources (PGR) are essential for meeting the demand for future food security. Advances in biotechnology have generated new opportunities for the conservation and utilization of genetic resources. Techniques like in vitro culture and cryopreservation have made it easier to collect and conserve genetic resources, especially of species that are difficult to conserve as seeds.
The use of molecular markers to measure the extent of variation at the genetic level, within and among populations, is of value in guiding genetic conservation activities and developing breeding populations in crops. This is so because most of the important plant species, specifically in developing countries are at risk of extinction and also there is little knowledge about them or of their potential for improvement. They may contain valuable genes that confer adaptation or resilience to stresses, such as heat tolerance or disease resistance that may be useful for future generations. Modern biotechnologies and bioprospecting can help to counteract trends of genetic erosion in all food and agriculture sectors.
Reliable information on the distribution of genetic variation is a prerequisite for sound selection, breeding and conservation programmes. Genetic variation of a species or population can be assessed in the field or by studying molecular and other markers in the laboratory. A combination of the two approaches is required for reliable results. Molecular markers are identifiable DNA sequences, found at specific locations of the genome and associated with the inheritance of a trait or linked gene. Molecular markers can be used for (a) mapping of genes, b) marker-assisted breeding, (c) understanding and conserving genetic resources, and (d) genotype verification. These activities are critical for the genetic improvement of crops, fruits and forest trees.
Breeding and reproducing crops and trees
Conventional breeding, relying on the application of classic genetic principles based on the physical characteristics of the organism concerned, has been very successful in introducing desirable traits into crop cultivars from domesticated or wild relatives or mutants. Such phenotype-based selection is a slow, demanding process and is expensive in terms of both time and money. Biotechnology on the other hand can make the application of conventional breeding methods more efficient.
Micropropagation involves taking small sections of plant tissue, or entire structures such as apical shoots, axillary/nodal buds, and culturing them under artificial conditions to regenerate complete plants. The technology is particularly useful for maintaining valuable genetic make-up of plants, breeding otherwise difficult-to-breed species (e.g. many trees), disease elimination and speeding up plant breeding and providing abundant plant material for research and use.
In vitro selection
This refers to the selection of germplasm by applying specific selection pressure to cultured tissues under laboratory conditions. Many recent publications have reported useful correlations between in vitro responses and the expression of desirable field traits for crop plants, most commonly disease resistant. Positive results are available also for tolerance to herbicides, metals, salt and low temperatures. With the accelerating changes in the climatic patterns, this method is likely to be very useful in agricultural research involving screening for disease resistance and tolerance to salt, frost and drought.
Genetic linkage maps can be used to locate and select for genes affecting traits of economic importance in plants. The potential benefits of marker-assisted selection (MAS) are greatest for polygenic traits that are controlled by many genes, such as fruit yield, wood quality and traits which are difficult to score, time consuming and expensive like disease resistance. Markers can also be used to increase the speed or efficiency of selecting introduced new genes from one population to another. When the desired trait is found within the same species such as two varieties of sweet potato, it may be transferred with traditional sexual hybridisation techniques followed with molecular markers assisted selection to track the desired gene.
When the desired trait is found in an organism that is not sexually compatible with the host, it may be transferred using genetic engineering. Three distinctive types of genetically modified crops exist: (a) “distant transfer”, in which genes are transferred between organisms of different kingdoms (e.g. bacteria into plants); (b) “close transfer”, in which genes are transferred from one species to another of the same kingdom (e.g. from one plant to another); and (c) “tweaking”, in which genes already present in the organism’s genome are manipulated to change the level or pattern of expression. This sometimes may also involve stopping altogether normal function of a gene, commonly known as gene silencing. Once the gene has been transferred, the crop must be tested to ensure that the gene is expressed properly and is stable over several generations of breeding. This screening can usually be performed more efficiently than for conventional crosses because the nature of the gene is known, molecular methods are available to determine its localization in the genome and fewer genetic changes are involved.
The most significant breakthroughs in agricultural biotechnology are coming from research into the structure of genomes and the genetic mechanisms behind economically important traits. The rapidly progressing discipline of genomics is providing information on the identity, location, impact and function of genes affecting such traits – knowledge that will increasingly drive the application of biotechnology in agriculture.
Diagnostics and epidemiology
Plant and animal diseases are difficult to diagnose because the signs may be misleading or even entirely absent until serious damage has occurred. Advanced biotechnology-based diagnostic tests make it possible to identify disease-causing agents and to monitor the impact of disease control programmes to a degree of precision not previously possible. Molecular epidemiology characterizes pathogens by nucleotide sequencing, which enables their origin to be traced. This is important for epidemic diseases, in which the possibility of pinpointing the source of infection can significantly contribute to improved disease control. Enzyme-linked immunosorbent assay (ELISA) tests have become the standard methodology for diagnosis and surveillance of many diseases worldwide, and polymerase chain reaction (PCR) based diagnostic kits are especially useful and precise in diagnosing plant diseases and various biotypes of causal organisms. These kits are proving increasingly useful also for livestock and fish diseases.
Next week, we will focus on “Opportunities for PNG and Biotechnological Activities carried out by various PNG R&D institutions”.