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N.I. Vavilov’s theories direct present-day global activities in plant science, breeding, and conservation. His expeditions around the world located centers of diversity of crop evolution. Vavilov was one of the earliest scientists to realize that wild genetic diversity could be lost, through genetic erosion, reducing the possibilities for future crop improvement. To measure genetic erosion, Gary Nabhan and colleagues traveled in 11 countries following routes that Vavilov had taken more than half a century before. The detailed notes concerning the vegetation and flora that Vavilov observed could be used as a baseline in contrast with Nabhan’s plant and cultivar inventories to observe changes in plant diversity at specific sites. The objective of this manuscript is to summarize potential genetic erosion at three case study locations, the Pamiri Highlands of Tajikistan, the Ethiopian Highlands, and the Colorado Plateau of Southwestern North America. At these localities Vavilov’s notes can be compared with the agricultural activities of the modern day. In each case, significant climatic, environmental, and human-caused changes have affected the local agriculture during the intervening years. Localities that have retained diversity have suffered the least. Reduction of diversity is associated with decreased agricultural stability and productivity. Programs encouraging farmers to manage diversity and promote involvement of local youth in agriculture may reduce or moderate the effect of genetic erosion.

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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.

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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.

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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.

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We contrasted the effect of liquid nitrogen (LN2), sulfuric acid (H2SO4), and a nontreated control on the germination of six Rubus species. We also were interested in determining if LN2 could be an effective mechanical scarifying agent for these species. Seeds of each species were treated with three 3-minute dips in LN2 with alternating 10-minute thaws, with H2SO4 for 30 minutes, or left untreated. The percent germination of R. multibracteatus A. Leveille & Vaniot, R. parviflorus Nutt., R. eustephanos Focke ex Diels, R. leucodermis Douglas ex Torrey & A. Gray, R. ursinus Cham. & Schldl., and R. chamaemorus L. treated with LN2 was not significantly different than the control. Germinated seedlings from the LN2 treatment of each species showed normal development upon planting, indicating that long-term cryogenic preservation of these Rubus species seeds may be possible. The H2SO4 treatment significantly increased the rate and percentage of germination in R. parviflorus, R. eustephanos, R. leucodermis, and R. ursinus over that of the control and the LN2 treatment. The alternative LN2 application techniques that have been attempted thus far have not significantly improved Rubus seed germination compared with that of the control.

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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.

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