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N.I. Vavilov, Academician of the V.I. Lenin All-Union Academy of Agricultural Sciences, takes his place as a founding pillar of knowledge in the cathedral of the origin and development of cultivated plants. Relying on the theories of his revered predecessors, Charles Darwin and Alphonse de Candolle, Vavilov developed the concept of centers of origin for agronomic crops. Vavilov’s astute hypotheses set the stage for the modern use of exotic germplasm in plant breeding. Vavilov, a devoted scientist, continued to revise and refine his theory of the centers of origin throughout his lifetime based on additional plant collections and data evaluation. Though he initially proposed three in 1924, and eight in 1935, his final papers of 1940, discussed seven major centers with some minor additions. His concept of specific centers of origin for crop plants was not an isolated aphorism but has directed breeders, on their study and reflection, to the continued improvement and economic development of plants for humanity. Inherent genetic plant variability is the basis of domestication and breeding into crops of economic importance with food, fuel, fiber, and industrial uses. The objective of this article is to present a summary of Vavilov’s plant explorations. His collection trips led to the development of his theory of the centers of origin of cultivated crops, the law of homologous variation, as well as his concept of genetic erosion. Further modification of his theories by other scientists and the impact of his ideas are mentioned. His influence on present day conservation of genetic resources are presented.
Many Rubus species have a seedcoat imposed exogenous dormancy. Our objective was to contrast the effect of liquid nitrogen (LN2), sulfuric acid (H2SO4), and an untreated control on seed germination of R. multibracteatus A. Leveille & Vaniot and R. parviflorus Nutt. and to determine if LN2 could be used as a mechanical scarifying agent for these species. Three replicates of 100 seeds of each species were treated with either three 3-min dips in LN2 with corresponding 10 min thaws or for 30 min with H2SO4 or were left untreated. The LN2 pretreatment did not significantly reduce the viability of R. multibracteatus or R. parviflorus as compared to the control. A random sample of germinated R. multibracteatus from the LN2 pretreatment showed normal seedling development upon planting. The H2SO4 pretreatment significantly increased germination percentages as compared to the control or LN2 pretreatment as well as for R. ursinus Cham. & Schldl. and R. eustephanus Focke ex Diels. The LN2 treatment did not significantly improve germination over the control group and therefore was not an effective scarifying agent as applied to R. multibracteatus or R. parviflorus. However, these two Rubus species were not damaged by repeated dips in LN2. Alternative LN2 pretreatments are being examined for their potential to improve Rubus germination further.
Chromosome numbers were determined for the Rubus species and cultivars held at the USDA/ARS National Clonal Germplasm Repository, Corvallis, Ore. Counts were made on a total of 205 taxa; 81 of which were new, 124 were corrections, and a few were corrections of previous reports. The numbers ranged from 2n = 2x = 14 to 2x = 98, and included odd-ploids and aneuploids. Knowledge of the chromosome number of a plant is important for its use in breeding because of potential sterility problems that may arise due to unbalanced gametes. The value of these particular counts are that they are vouchered by a permanent, living plant collection that is available to the scientific user community.
The Pacific Northwest boasts a remarkable diversity of wild currants and gooseberries (Ribes). Of nearly 150 species worldwide, 34 occur in the region. All but two infrageneric taxa are represented, including close relatives of the black currants, red currants, and cultivated gooseberries. High ecological diversity parallels this taxonomic diversity: a Ribes species occurs in nearly every terrestrial habitat, from sea level to above treeline, and from swamp to desert. This diversity is a valuable source of agronomically important genes for the plant breeder. In addition, wild Ribes represent a relatively unexplored source of ornamental shrubs. Habit and habitat of a number of species of interest are described and illustrated. An annotated list of species, subspecies, and varieties native to the Pacific Northwest is presented with discussion of taxonomic proximity to Cultivated varieties, range, natural habitat, and ornamental potential.
During research to develop a new germination protocol for Rubus being conducted at the National Clonal Germplasm Repository in Corvallis, we observed mixed responses to sodium hypochlorite (NaOCl) as a seed scarifying agent. For R. parviforus Nutt., scarification with NaOCl resulted in 34% germination. Fewer than 1% of the seedlings showed any negative effects after exposure to 2.6% NaOCl for 24 hours. But in R. ursinus Cham. & Schldl., R. multibracteatus A. Leveille & Vaniot, R. swinhoei Hance, and R. setchuenensis Bureau & Franchet, the percentage of injury observed ranged from 40% to 100%. In these cases, although embryonic tissue did not appear necrotic, the radicle and plumule failed to elongate after emergence. The epicotyl or primary leaves did not develop, and the radicle failed to form root hair. The cotyledons, apparently unaffected, opened and were a healthy green. NaOCl did not kill the embryo, but deterred development of the embryonic axis. As a result of the NaOCl scarification the cotyledons expanded yet the seedlings eventually died.
Recent USDA plant collecting expeditions to Ecuador; the People's Republic of China, and within North America, have obtained a number of lesser known wild Rubus species. These, and additional species, are preserved as seedlots with some plant representatives, at the USDA-ARS National Clonal Germplasm Repository-Corvallis. In this study, the seed size of 40 Rubus species was measured and contrasted. The average weight of the largest-seeded species of the study group, R. megalococcus Focke, an Ecuadorean blackberry, was 24.2 mg; European blackberry, R. procerus Muller, was 3.0 mg. The average weight of other European and North American blackberry and raspberry seed ranged from 2.7 to 1.3 mg. Asian raspberry species tended to be the smallest, ranging from R. coreanus Miq. at 1.2 mg to R. eustephanus Focke ex Diels at 0.3 mg. Several of the smaller seeded Asian species such as R. formosensis Kuntze, R. minusculus A. Leveille & Vaniot, R. hirsutus Thunb., and R. eustephanus had many drupelets, which may be a heritable trait to benefit yield through breeding for increased fruit size.
In the late 1800s a European disease called white pine blister rust, Cronartia ribicola Fisher, was introduced into the United States. By 1937 this disease had naturalized and was firmly established in native Ribes across the country. White pine blister rust causes economic damage to white pines and infects leaves of some Ribes late in the summer after harvest. Ribes serve as obligate alternate hosts for this disease. Our objective was to determine which Ribes species were susceptible to white pine blister rust under field conditions in Corvallis, Ore., where inoculum is naturally present. In 1995 and 1996, 57 Ribes taxa from North and South America, Europe, and Asia, were evaluated in mid-August and mid-September for presence of white pine blister rust. Susceptibility was determined by the rust infection of the abaxial leaf surfaces. Rust infection was rated on a scale from 1, no infection observed, to 9, severe infection covering almost the entire surface of at least three or more leaves. Data from 1995 indicated that 22 Ribes taxa were susceptible to white pine blister rust, while 35 others had no infection. The 1996 data will be reported. Species without infection may offer resistance genes to breeders who wish to develop rust-resistant commercial fruit cultivars.
Populations of 40 Rubus sp., representing the Malachobatus, Idaeobatus, Eubatus, and Anoplobatus, were planted in the field in 1994. To get a preliminary idea of how successful crosses between these species and standard cultivars would be, 58 crosses were attempted between standard cultivars and randomly selected genotypes of the 14 species that produced a significant number of flowers in 1995. Diploid species were crossed with `Tulameen' and `Meeker' raspberry and the tetraploid species with `Cherokee' and `Chester' blackberry. Twenty-two crosses produced seed lots ranging from 8 to 630 seeds. Crosses were successful with R. caesius, R. caucasicus, R. coreanus, R. georgicus, R. parvifolius, R. rosifolius, and R. sumatranus. Crosses were not successful with R. eustephanos, R. insularis, R. innominatus, R. lambertianus, R. sachalinensis, R. setchuenensis, R. swinhoei, and R. tsangorum. In vitro seed germination was attempted with all crosses. Larger seed lots were also germinated using standard procedures for Rubus. There is a great deal of variability in leaf morphology of the young seedlings within a cross that suggests that some or all of the seedlings are true hybrids. Seedlings that are not true hybrids could result from contaminant pollen or, as in R. armeniacus, pseudogamous embryo formation. Crossing results from 1995 and 1996, including crosses attempted and seed numbers per cross, will be presented along with, for the 1995 crosses, the number of germinated seedlings and our assessment of whether they appear to be true hybrids.
Many lesser-known wild Rubus species from Ecuador, the People's Republic of China, and North America have been obtained on recent U.S. Dept. of Agriculture plant-collecting expeditions. In this study, the seed size of 43 Rubus species was measured. An 80-fold range in seed weight was observed within the genus. Asian species in the subgenera Idaeobatus and Malachobatus had the lightest seed, ranging from 0.3 mg (R. eustephanus Focke ex Diels) to 1.2 mg (R. coreanus Miq.). The seeds of ≈80% of the species examined weighed <2 mg. Seeds of European species in the subgenera Idaeobatus and Rubus (formerly Eubatus of Focke) ranged from 1.3 to 3.0 mg. The South American Orobatus included several of the heaviest-seeded species. Rubus megalococcus Focke (subgenus Rubus) had the heaviest and largest seed weighing 24.2 mg. Seed weight was not related to ploidy level in wild species. Seed weight and length were positively correlated. Seed flatness was not related to seed length. Several of the smaller-seeded Asian species, such as R. minusculus A. Lev. & Van., R. hirsutus Thunb., and R. eustephanus, had more drupelets per fruit than did those of larger-seeded species. This heritable trait may be useful in breeding for increased fruit size.
The National Plant Germplasm System (NPGS) of the U.S. Department of Agriculture (UDSA), Agricultural Research Service (ARS), has greatly expanded since 1980. Foremost in this expansion was the addition of seven repositories for clonally propagated fruit and specialty crops. Many collections at state agricultural experiment station sites were in jeopardy as breeders retired. These collections can now be preserved by the NPGS. The NPGS has provided funding for plant exploration and exchange. From 1980 to 2004, 37 exploration/exchange proposals for fruit crops were funded, and over 3000 accessions introduced as a result. Crop Germplasm Committees (CGCs), established for each commodity have prepared genetic vulnerability statements and prioritized collection activities. The USDA ARS, National Germplasm Resources Laboratory (NGRL), facilitates international relationships, and the USDA Animal and Plant Health Inspection Service (APHIS), National Plant Germplasm Quarantine Center (NPGQC), tests and makes pathogen-tested germplasm available. As a result of the Convention on Biological Diversity (1993) and the International Treaty on Plant Genetic Resource for Food and Agriculture (2004), the USDA now pursues germplasm collection through the establishment of bilateral agreements of mutual benefit.