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- Author or Editor: Philip L. Forsline x
The genetic diversity of a wild Malus population collected in the Kyrgyz Republic was compared with seedlings of Malus sieversii collected in Kazakhstan. Based on microsatellite marker results, we conclude that the population of 49 individuals collected in the Kyrgyz Republic includes private alleles and this population is assigned to a common genetic lineage with M. sieversii individuals found in the Karatau Mountain range of Kazakhstan. We recommend that a subset of these individuals be included in the National Plant Germplasm System Malus collection so they may be made available to breeders, physiologists, and other scientists for further examination.
Clonally propagated crops, unlike seed-propagated crops, require intense and costly maintenance, generally in ex situ field gene banks. Consequently, large germplasm collections of tree species especially, are difficult to conserve in a well-replicated fashion and are vulnerable to damage from environmental stresses. Accordingly, long-term storage in liquid nitrogen presents a viable conservation alternative. To assess effectiveness of one approach to cryopreservation, dormant buds from 64 apple (Malus ×domestica Borkh. and other Malus spp.) accessions were collected and preserved in liquid nitrogen using a dormant-vegetative-bud method. Buds were retrieved from liquid nitrogen storage, rehydrated, and grafted onto rootstocks to determine survival. Mean recovery was 76% for 40 cold-hardy accessions, 66% for 20 moderately cold-hardy accessions, and 24% for four cold-tender accessions (range: 16% to 100%). Only four accessions had ≤25% recovery while 54 accessions had ≤50% recovery and 35 accessions had ≤75% recovery. No significant decline in recovery of these accessions by bud grafting occurred after 4 years of liquid nitrogen storage.
Seeds and scionwood of Malus sieversii Lebed. have been collected from wild populations of apple trees in Kazakhstan. Seedlings and grafted trees were planted in the orchards at the U.S. Dept. of Agriculture Plant Genetic Resources Unit in Geneva, N.Y. We developed core collections to capture the genetic and phenotypic diversity represented in the trees from each of two of the Kazakhstan collection sites. These core collections capture more than 90% of the genetic diversity of the original populations, as determined using seven unlinked simple sequence repeat markers and 19 quantitative traits. Since phenotypic evaluations of these materials have been completed, the 35 trees within each population will be used as parents in crosses so that the genetic diversity in the orchard populations can be captured as seed for long-term ex situ conservation. This strategy of storing seeds, rather than maintaining costly field collections, could be applied to other collections of wild plant materials in the National Plant Germplasm System.
The USDA-ARS National Plant Germplasm System Malus collection is maintained by the Plant Genetic Resources Unit (PGRU) in Geneva, NY. In the 1990s, a core subset of 258 trees was hand-selected to be representative of the grafted Malus collection. We used a combination of genotypic and phenotypic data to compare the diversity of the 198 diploid trees in the original core subset with that of 2114 diploid trees in the grafted field collection for which data were available. The 198 trees capture 192 of the 232 total microsatellite alleles and have 78 of the 95 phenotypic characters. An addition of 67 specific individuals increases the coverage to 100% of the allelic and phenotypic character states. Several de novo core sets that capture all the allelic and phenotypic character states in 100 individuals are also provided. Use of these proposed sets of individuals will help ensure that a broad range of Malus diversity is included in evaluations that use the core subset of grafted trees in the PGRU collection.
Seeds from wild Malus orientalis trees were collected during explorations to Armenia (2001, 2002), Georgia (2004), Turkey (1999), and Russia (1998). Seedling orchards with between eight and 171 individuals from each collection location were established at the U.S. Department of Agriculture–Agricultural Research Service Plant Genetic Resources Unit (PGRU) in Geneva, NY. Genotypic (seven microsatellite markers) and disease resistance data were collected for the 776 M. orientalis trees. The genetic diversity of the 280 individuals from Armenia and Georgia was compared with data previously published for the M. orientalis individuals from Russia and Turkey. A total of 106 alleles were identified in the trees from Georgia and Armenia and the average gene diversity ranged from 0.47 to 0.85 per locus. The genetic differentiation among sampling locations was greater than that found between the two countries. Six individuals from Armenia exhibited resistance to fire blight (Erwinia amylovora), apple scab (Venturia inaequalis), and cedar apple rust (Gymnosporangium juniperi-virginianae). The allelic richness across all loci in the individuals from Armenia and Georgia was statistically the same as that across all loci in the individuals from Russia and Turkey. A core set of 27 trees was selected to capture 93% of the alleles represented by the entire PGRU collection of 776 M. orientalis trees. This core set representing all four countries was selected based on genotypic data using a modified maximization algorithm. The trees selected for the M. orientalis core collection will be added to the main field collection at the PGRU.
We estimate the minimum core size necessary to maximally represent a portion of the U.S. Department of Agriculture's National Plant Germplasm System apple (Malus) collection. We have identified a subset of Malus sieversii individuals that complements the previously published core subsets for two collection sites within Kazakhstan. We compared the size and composition of this complementary subset with a core set composed without restrictions. Because the genetic structure of this species has been previously determined, we were able to identify the origin of individuals within this core set with respect to their geographic location and genetic lineage. In addition, this core set is structured in a way that samples all of the major genetic lineages identified in this collection. The resulting panel of genotypes captures a broad range of phenotypic and molecular variation throughout Kazakhstan. These samples will provide a manageable entry point into the larger collection and will be critical in developing a long-term strategy for ex situ wild Malus conservation.
Genetic diversity and disease resistance are described for 496 seedlings from wild populations of Malus orientalis Uglitzh. collected in southern Russia and Turkey in 1998 and 1999. Eighty-five half-sib families were genotyped using seven microsatellite markers, and disease resistance was determined for apple scab (Venturia inaequalis Cooke), cedar apple rust (Gymnosporangium juniperi-virginianae Schwein), and fire blight (Erwinia amylovora Burrill). Individuals from the two Russian Caucasus collection locations were homogeneous compared with populations from the four Turkish collection locations. Within three of the Turkish collection locations, some half-sib families were highly diverse and several of these families had unusually high levels of disease resistance. In all, twenty individuals exhibited resistance to all three diseases. Bayesian analyses of the population structure revealed six distinct clusters. Most of the individuals segregated into two clusters, one containing individuals primarily from southern Russia and the other containing individuals from both Russia and northern Turkey. Individuals in the four small clusters were specific to Turkish collection locations. These data suggest wild populations of M. orientalis from regions around the Black Sea are genetically distinguishable and show high levels of diversity.