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Abstract
Although there are several ways to discuss mechanization of crop production, I have chosen the evolutionary approach. Mechanization goes through evolutionary stages. As new crops are mechanized, the intermediate steps could be by-passed if the evolutionary pattern is understood. Let us examine some of the steps taken in mechanization with various vegetable crops.
Curators of plant genetic resources collections must preserve germplasm possessing known useful characteristics as well as material displaying general genetic diversity. In order to ensure that both types of germplasm are included in a collection, germplasm curators require three fundamental types of information about each accession: taxonomic identity, genetic identity, and genetic relationship. Because simple sequence repeat DNA fragments (SSRs) have been successfully used to determine the genetic identity of grape clones, we conducted a study to determine if SSRs would supply all three types of information for the accessions in the cold-hardy Vitis (grape) germplasm collection. SSR fragments were amplified at six different loci for 23 accessions of cold-hardy grape spanning the range of species diversity in the collection. The minimum number of different alleles found at a locus was 9; the maximum was 26. Heterozygosity values ranged between 0.565 and 0.783, while gene diversity values were in the range 0.785 to 0.944. Two hundred fifty-two pairs of plants out of a possible 253 could be distinguished by their SSR profiles. Nei's genetic identities were computed between all pairs of plants and used in a UPGMA cluster analysis. The relationships obtained did not correspond well to expected relationships based on geography and taxonomy. Four species of grapes were represented by two or more accessions in this study. No DNA fragments found at these six loci served to unambiguously distinguish one species from another. Thus, SSR fragments from the six loci studied were useful in determining genetic identity of accessions, but were not helpful in determining genetic relationships or taxonomic identities. We are searching for additional loci that are informative for these types of information. Meanwhile we highly recommend SSRs for determining genetic identity in germplasm resources collections.
The USDA-ARS Vitis genetic resources collections in Geneva, N.Y., and Davis, Calif., contain ≈3600 accessions of >35 species. Accurate and unambiguous identification of these grapes is essential for efficient and effective use of this germplasm. Previous workers have successfully used polymerase chain reaction (PCR)-generated SSRs to fingerprint cultivars of the wine and table grape species, V. vinifera. Building on this work, we conducted a test of five previously characterized SSR loci on 110 accessions of 25 grape taxa (21 Vitis species and 4 hybrids) to determine if they would satisfy our need for identifying cultivars within the USDA-ARS grape collections. Scorable SSR fragments were produced with all 550 primer-accession combinations, with no null loci observed. The loci were highly polymorphic, with 16 to 38 different alleles found at a locus. Heterozygosity values ranged from 0.464 to 0.818, while gene diversity values ranged from 0.875 to 0.955. Discrimination power at a locus varied from a low of 0.947 to a high of 0.987. Combined discrimination power of all loci was effectively 1.000, with 2 chances in 100,000,000 that two sexually, independently derived grape accessions would not be distinguishable using this set of five SSR loci. Two plants in the study that had previously been classified as belonging to different grape species were shown to have identical SSR fingerprints, showing that they almost certainly possessed the same genotype. Because SSR markers are codominant and highly polymorphic and SSR loci are generally conserved across a range of related species, we strongly recommend SSRs for fingerprinting not only grape, but other clonal genetic resources collections as well.
Abstract
Root dips of tomato transplants in slurries of activated carbon provided significant but not total protection from a 1 lb./A simulated residue of atrazine in the soil. Although activated carbon slurries did not damage roots, direct contact with the foliage caused severe injury.
Abstract
Eight stamenless tomato mutants (Lycopersicon esculentum Mill.) were intercrossed in a half-diallel design to determine allelic relationships. Two allelic series were represented among the mutants. One series included sl, sl 2 , sl 5, cs, and fl. The 2nd series included bn, sl?, and pms. No allelic interactions occurred between members of the 2 series. Fruit and seed set resulting from cross-pollinations varied greatly among the mutants. The stamenless types, with the exception of sl 2, do not appear to be promising for use in producing hybrid tomato seed because of poor fruit and seed set.
Eight taxa of Salvia L., representing broad geographic origin and diversity within the genus, were grown under long day conditions for 36 d at 15-h days of 20, 25, 30, 35, or 40 °C and 9-h nights of 15 or 25 °C. Taxa of European origin displayed broader tolerance to high day temperatures (DTs) with the lowest relative reduction in growth and net photosynthesis (Pn) occurring at DTs 30 °C or greater compared with those native to North and South America. Salvia splendens Sell. ex Roem. & Schult. (scarlet sage) was particularly intolerant of high temperatures with all plants dying at days of 40 °C. All plants of S. nemorosa L.‘Ostfriesland’ (‘Ostfriesland’ wood sage), S. pratensis L. (meadow sage), and S. × sylvestris L. ‘Mainacht’ (‘May Night’ salvia) survived at days of 40 °C with no visual signs of injury, whereas all other taxa except S. splendens exhibited stunted, contorted growth with foliar chlorosis and necrosis at 40 °C. Day temperature exerted the primary effect on top growth, root growth, and Pn of all taxa. Night temperature effects were significant for some taxa but were of less importance than day temperature.