| dc.description.abstracteng | In the context of conservation and use of plant genetic resources, both storage in gene banks (ex situ) and
safeguard on-farm (in situ) are important concepts. Increasingly attention focuses on the on-farm
management of plant genetic resources as a dynamic maintenance strategy. To date, little is known about
the potential of ‘evolutionary’ adaptation to site-specific conditions and the mechanisms involved. Lentil
is an autogamous food legume crop with limited recombination. In long-term experiment three old lentil
cultivars were exposed to ten generations of natural selection at three farms in Central and Northern
Germany under rain-fed conditions. Two of the selection sites were on soils with low fertility and expected
frequent shortages in water supply during the growing season. The following four main questions were
investigated: i) Did natural selection during ten generations lead to site-specific adaptation in terms of
yield? ii) Did natural selection alter phenotypic and genotypic variability? iii) What is the importance of
seed weight for natural selection and adaptation? iv) Was drought a significant factor for site-specific
development?
The three lentil cultivars are distinctly different in their morphological and phenological traits. Populations
in the fifth and tenth generation under site-specific natural selection within each cultivar and the
corresponding initial material were compared in a two-year field trial at the three selection sites. Singleplant
progeny testing during two years at one location and SNP genotyping using KASPar™ assays was
done to assess phenotypic and genotypic within-population variability. Selections for extreme seed size
for six generations from each cultivar were phenotyped in the field and genotyped by SNP markers.
Additionally, populations in the tenth generation of natural selection were tested in induced drought in
rainout shelters for their variation in drought stress tolerance during three years at one location.
Significant continuous site-specific changes in seed weight and flowering time in both directions were
observed for one cultivar. Natural selection at the more stress-prone location led to a lower seed weight
and earlier flowering, whereas in the most fertile location selection favored larger seeded genotypes and
later flowering. However, these changes did not lead to a significant site-specific adaptation in terms of
yield. But a general yield advantage across locations for the population with a lower seed weight and
earlier flowering was observed. A general tendency towards better yield for the latest generations across
cultivars and locations suggests that natural selection was positive in terms of the general performance.
Phenotypic and genotypic variation within the initial material of one cultivar goes back to three main
genotypes, which differ significantly in seed weight and flowering time. The observed phenotypic changes
and site-specific differences in the genetic variability are supposedly caused by different selection pressure
at the three locations. However, at the most stress-prone location, within-population variability is
relatively high due to recombination, whereas the population selected at the most fertile location is highly
dominated by one genotype. Across all locations, the genetic variation within this cultivar was maintained.
The other two cultivars exhibited a very low genetic variability and were maintained at all three farms
without changing their characteristic seed weight significantly.
A general yield improvement by selection for larger seeds was observed in all cultivars. The full genetic
variation within one cultivar was maintained by the selection for both extremes in seed size. Selection
within two cultivars with very low genetic variability resulted in an unintended genetic modification from the initial material by selecting ‘off-types’, probably resulting from spontaneous outcrossing, with smaller
seeds in one case and with larger seeds in the other.
Significant site-specific variation in drought tolerance was not found. Thus, the effect of year may have
counteracted a continuous site-specific adaptation or selection sites are not as distinctly different as
expected in water regimes. Consequently, the main factors involved in the continuous site-specific changes
in one cultivar remain unidentified. It was observed that cultivars reacted differently to drought
conditions.
On-farm management with lentil can lead to a site-specific development and site-specific adaptation may
occur in the long-term. Given a substantial genetic variability, seed yield, straw yield, harvest index, seed
weight, and flowering time were altered significantly by natural selection.
Our results prove the maintenance and management on-farm of plant genetic resources in an autogamous
species a dynamic management strategy. For the maintenance of material with substantial genetic
diversity, at least two farms with significantly different environmental conditions are necessary.
Homogeneous accessions, when combined with ex situ maintenance, could be managed at one location. I
recommend the characterization of the material in advance for its genetic diversity and outcrossing
potential to establish a well-grounded management strategy accordingly. Different material of the same
crop should not be maintained at one farm. Selection for traits considered negative for agronomic
performance and monitoring of characteristic traits may be considered to preserve the integrity of the
material and/or to improve its agronomic performance. To study the main factors involved in site-specific
adaptation by natural selection for autogamous crops, I suggest using genetically broad populations, which
should be well characterized in advance, phenotypically as well as by molecular markers, to monitor their
spatial and temporal development in diverse environments. | de |