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ABSTRACT: Malus sieversii (Lebed.) M. Roem. is a wild progenitor species of the domesticated apple. It is found across a mountainous region of central
Asia and has been the focus of several collection expeditions by the USDA-ARS-National Plant Germplasm System. This study
used microsatellite variation at seven loci to estimate diversity and differentiation within M. sieversii using several complimentary approaches. Multilocus genotypes were amplified from 949 individuals representing seedling trees
from 88 half-sib families from eight M. sieversii populations collected in Kazakhstan. Apportioning of genetic variation was estimated at both the family and site level. Analyses
using a hierarchical model to estimate F
st showed that differentiation among individual families is more than three times greater than differentiation among sites.
In addition, average gene diversity and allelic richness varied significantly among sites. A rendering of a genetic network
among all sites showed that differentiation is largely congruent with geographical location. In addition, nonhierarchical
Bayesian assignment methods were used to infer genetic clusters across the collection area. We detected four genetic clusters
in the data set. The quality of these assignments was evaluated over multiple Markov Chain Monte Carlo runs using both posterior
likelihood and stability of the assignments. The spatial pattern of genetic assignments among the eight collection sites shows
two broadly distributed and two narrowly distributed clusters. These data indicate that the southwestern collection sites
are more admixed and more diverse than the northern sites.
Tree Genetics & Genomes 04/2012; 5(2):339-347. · 2.34 Impact Factor
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ABSTRACT: With 3 figures and 4 tablesAbstractPenicillium expansum and Colletotrichum acutatum cause blue mould and bitter rot of apples during storage which results in significant economic losses. Resistance to these pathogens in commercial apple cultivars has not been documented in the literature. An apple germplasm collection, from the centre of origin in Kazakhstan, is maintained in Geneva, New York. This collection represents a more diverse apple gene pool than commercial cultivars and was evaluated for resistance to the pathogens that cause blue mould and bitter rot. Resistance reactions were skewed towards susceptibility for both fungi and comprised the majority of accessions examined. However, resistance to P. expansum was confirmed in select accessions over multiple years. Maturation patterns and quality indices for soluble solids and acidity, which may also affect susceptibility, were highly variable and represent the genetic diversity of the germplasm collection. Resistance in four accessions to C. acutatum and two accessions resistant to both P. expansum and C. acutatum are reported here for the first time. Data from this study will serve as a foundation for conventional apple breeding programmes and molecular genetics investigations to provide resistance against blue mould and bitter rot in commercial apple varieties.
Plant Breeding 07/2011; 130(4):481 - 486. · 1.60 Impact Factor
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07/2010: pages 1 - 61; , ISBN: 9780470650868
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ABSTRACT: Plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), is an important apple, Malus domestica Borkh., pest that significantly hinders sustainable apple production in eastern North America. The potential for host plant resistance to plum curculio among apple germplasm has never been rigorously evaluated. Thus, studies were conducted to assess the susceptibility of a number of exotic and domestic Malus accessions housed at the USDA Plant Genetic Resources Unit (PGRU) "core" collection in Geneva, NY. Contrary to earlier published reports and promising data from a field assessment in 2005, these results suggest that there is probably little potential for genetic resistance to plum curculio among the Malus germplasm collection evaluated. More specifically, four Malus hybrid selections that have previously been released with claims of plum curculio resistance were shown to be susceptible to plum curculio attack. Because there are additional accessions housed at PGRU outside of the core collection that are currently classified as resistant, further studies are necessary to evaluate the true resistance qualities of these releases. It is also important to clarify such discrepancies in both the USDA online Germplasm Resources Information Network and in the horticultural literature. Although other Malus species exhibited some variability in fruit susceptibility, none could be classified as being truly resistant to plum curculio attack by any definition that would have relevance to commercial production and sale of apples.
Journal of Economic Entomology 11/2007; 100(5):1663-71. · 1.70 Impact Factor
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ABSTRACT: 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.
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ABSTRACT: 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.
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ABSTRACT: Blue mold of apples, incited by Penicillium expansum, causes extensive losses on stored apples worldwide. Despite the severity of this problem, apple breeders do not evaluate their crosses for resistance to this disease, because there has been little resistance to blue mold in the gene pool of the germplasm used. A new apple germplasm collection from the center of origin in Kazakhstan, maintained in Geneva, NY, and representing a much broader gene pool, was evaluated for resistance to blue mold. Apples were harvested from the Elite collection trees that were clonally propagated from budwood collected in Kazakhstan and from seedling trees originating from seeds of the same trees as the Elite budwood or from other wild seedling trees in Kazakhstan. Fruit from 83 such accessions were harvested at the preclimacteric to climacteric stage, wound-inoculated with P. expansum at 103, 104, and 105 mL-1 conidial suspension, incubated for 5 d at 24 °C, and evaluated for decay incidence and severity. Two accessions were classified as immune (no decay at 103 and 104 mL-1), four as resistant (no decay at 103 mL-1), 53 as moderately resistant (lesions less than 10 mm at 103 mL-1), and 24 as susceptible. There were positive correlations (r = 0.92, 0.86, and 0.91) between decay severity and all three inoculum levels. Our results indicate a greater genetic diversity among the Kazak apple collection than among cultivated apples as evidenced by their broad range of fruit maturity, quality, and disease resistance patterns. The immune and resistant accessions may serve as a source of resistance in breeding programs and can be useful in explaining the mechanism of resistance to blue mold in apples.
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ABSTRACT: 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.
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