Conservation and monitoring of pgrs and gene banks

Pgrs and gene banks

1. Conservation and monitoring of PGRs and GENE Banks The monitoring and evaluation of plant material is necessary for the conservation of PGRs. There may be a big difference between the phenotype and the genotype in a population. With improved biotechnology methods, like the assignment of molecular markers, the gene level is of increasing interest. Ex situ conservation Ex situ conservation stands for all conservation methods in which the species or varieties are taken out of their natural habitat and are kept in surroundings made by humans. Large collections started with the activities of the Russian scientist N. I. Vavilov at the beginning of the last century. Even at that time the employment of ex situ measures was necessary because of the rapidly increasing gene erosion of landraces and other plants. Alongside these collections, plant breeders contributed to maintenance by collecting breeding material. This material was often kept in specific institutions, the first-called “gene banks” in the 1970s. They were established for the collection, maintenance, study, and supply of genetic resources of cultivated plants and related wild species. Gene banks maintain the plant material as seeds, in vivo (when the storage of seeds is difficult) or in vitro (mostly through cryoconservation ). In contrast to the cultivation of plants in botanical gardens, the work in gene banks is more engaged in intraspecific variability. Unfortunately, a lot of the material stored in gene banks is not in good condition and urgently needs to be rejuvenated. In situ conservation As well as ex situ conservation, there is also the attempt to save biodiversity and therefore PGRs in ecosystems ( in situ ). This can occur in the natural habitat (especially wild relatives and forestry species) or in locations where the plants (landraces and weeds) have evolved (on farms, in agroecosystems). As opposed to ex situ conservation in gene banks where only a section of the whole diversity is covered, the in situ approach is able to save larger parts of biological diversity.

2. Characterization and evaluation of plant genetic resources The yield levels of many crops have reached a plateau due to the narrow genetic base of these crops. Although the results of some surveys indicate that the genetic base of several important crops is beginning to increase in recent years, breeding programs of many important crops continue to include only a small part of the genetic diversity available, and the introduction of new and improved cultivars continues to replace indigenous varieties containing potentially useful germplasm. To widen the genetic base for further improvement, it is necessary to collect, characterize, evaluate, and conserve plant biodiversity, particularly in local, underutilized, and neglected crop plants. Morphological and agronomic characteristics are often used for basic characterization, because this information is of high interest to users of the genetic diversity. Such characterization requires considerable amounts of human labor, organizational skills, and elaborate systems for data documentation although it can be done by using simple techniques and can reach a high sample throughput. Quantitative agronomic traits can be used to measure the differences between individuals and populations with regard to genetically complex issues such as yield potential and stress tolerance. The diversity of a population, considering such complex issues, can be described by using its mean value and genetic variance in statistical terms. The traits detected are of great interest, but are frequently subject to strong environmental influences, which makes their use as defining units for the measurement of genetic diversity problematic. Molecular methods can be employed to characterize genetic resources and for the measurement of genetic variation. The major advantage of molecular methods for characterization is their direct investigation of the genotypic situation, which allows them to detect variation at the DNA level, thereby excluding all environmental influences. They can also be employed at very early growth stages.

3. Examples of successful uses of plant genetic resources Over the last few decades, awareness of the rich diversity of exotic or wild germplasm has increased. This has lead to a more intensive use of this germplasm in breeding ( Kearsey 1997) and thereby yields of many crops have increased dramatically. The introgression of genes that reduce plant height and increase disease and viral resistance in wheat provided the foundation for the Green Revolution and demonstrated the tremendous impact that genetic resources can have on production (Hoisington et al. 1999). In Germany, PGR material stored in the Gatersleben gene bank has been successfully used for the development of improved varieties . Developing improved varieties using gene bank materials takes a long time. For instance, when developing disease-resistant material, the resistance must be located with great expenditure of time and effort, from extensive collections. The experience in Gatersleben indicates that it take roughly 20 years between the first discovery of the material and the launching of a new variety , even if modern breeding methods are employed (Hammer 2004). A positive correlation has been observed between the number of evaluated accessions in gene banks and the number of released varieties on the basis of evaluated material (Hammer et al. 1994). The use of Turkish wheat to develop genetic resistance to diseases in Western wheat crops was valued in 1995 at US$50 million per year . Ethiopian barley has been used to protect Californian barley from dwarf yellow virus, saving damage estimated at $160 million per year . Mexican beans have been used to improve resistance to the Mexican bean weevil, which destroys as much as 25% of stored beans in Africa and 15% in South America ( Perrings 1998).