玉米精播机漏播补偿系统设计

目前玉米免耕播种机的播种质量仍低于常规播种。本文讨论了微机控制的排种监测及漏播补偿装置，通过机电结合手段解决漏播问题。台架试验表明本装置能够准确发现漏播，并通过采取的措施实现及时补种，补种成功率可达90％以上。     

Genetic Diversity and Population Structure in the Heavily Exploited Korean Rockfish,Sebastes schlegeli,in Korea

The Korean rockfish, Sebastes schlegeli, is a valuable and intensively exploited species in Korea. We discuss the genetic diversity and genetic structure of four Korean rockfish populations using eight microsatellite loci. In total, 161 different alleles from 138 individuals were observed. Average allele number per locus ranged from 2.5 to 23 and allelic richness varied from 13.38 to 14.63 within a population. Despite a long history of stocking practices, we found very high levels of polymorphism (mean heterozygosity = 0.810), which is comparable to other congeneric species. No significant difference in genetic diversity and molecular genetic variance (F_ST and R_ST) was observed among four local samples (P > 0.1). Little indication of contemporary inbreeding (F_IS= 0.051) or population structure (K = 1) was detected. This absence of differentiation may reflect high levels of gene flow along the coast of Korea. Our study demonstrates that rockfish in Korea should be managed as a single unit. Currently, the species does not appear to be genetically threatened, but the potential for a rapid loss of genetic diversity remains. This information on the genetic characteristics of Korean rockfish populations has important implications for fisheries management and conservation efforts, and will aid in the sustainable exploitation of the fishing resources and the preservation of biodiversity.     

Systemic accumulation of novel proteins in the apoplast of the leaves of potato plants following root invasion by the cyst-nematode Globodera rostochiensis

Systemic changes in gene expression have been analysed in potato plants following root infection with the cyst nematode Globodera rostochiensis. Root invasion by the pathogen induced major changes to occur in the composition of proteins extracted in intercellular fluid from the leaf apoplastic space. The changes involved the disappearance of innate leaf proteins and the accumulation of novel gene products. Analysis by SDS-PAGE indicated that the leaf polypeptides induced on nematode invasion are not cultivar or nematode pathotype-specific. Aspirin treatment of leaves induced a similar pattern to that induced systemically by nematodes, but several gene products were specific for the latter method of induction. In particular, two abundant [¹²⁵I]-Con A binding polypeptides of high M_r accumulated in intercellular fluid only on aspirin treatment. The results are discussed in the context of the role of the extracellular leaf proteins and their modulation by systemic signals.     

Reticuloendotheliosis virus integration in the fowl poxvirus genome: not a recent event

Integration of reticuloendotheliosis virus (REV) into the genome of fowl poxvirus (FPV) has been reported recently. With a view to determine whether this event had occurred in the past, we screened by polymerase chain reaction (PCR) for the presence of REV provirus in the DNAs of nine avian poxviruses, some of which had been lyophilized 50 yr ago. For REV, 5' long terminal repeat (LTR) and REV envelope sequences were amplified, whereas for FPV, the major envelope antigen gene and the region flanking REV sequences were amplified. In six of seven FPV strains examined, the specific PCR amplicons were obtained for both REV provirus and FPV sequences. One isolate in which presence of REV 5' LTR and envelope was not detected by PCR, a LTR remnant was detected by Southern hybridization. Interestingly, no REV sequence was detected in either canary poxvirus or pigeon poxvirus genome. These observations indicate that REV integration in the FPV genome is not a recent phenomenon but probably occurred prior to 1949.     

Effect of dietary selenium source, level, and pig hair color on various selenium indices

The first experiment evaluated the effects of feeding various levels of Se, two Se sources, and hair color on selenosis responses in growing-finishing pigs. The study conducted in two replicates was a 2 x 6 x 2 factorial arrangement in a split-plot design. Sodium selenite and Se-enriched yeast added at 0.3, 1, 3, 5, 7, and 10 ppm Se served as the main plot and pig hair color as the subplot. A total of 96 crossbred pigs were allotted and fed their treatment diets for a 12-wk period. White and dark (red or black) hair samples were collected from the dorsal-midline at the 4-, 8-, and 12-wk periods from one pig of each hair color from each treatment pen. Lower pig weights (P < 0.10) and daily gains (P < 0.05) occurred as dietary Se level increased when pigs were fed either Se source. Selenosis responses were somewhat more severe, when the inorganic Se source was fed. Alopecia and hoof separation were encountered after the 8-wk period when pigs were fed inorganic rather than organic Se. Plasma Se increased as dietary level increased (P < 0.01), when organic Se was provided (P < 0.01), and was higher (P < 0.05) when pigs were white-haired. A time x hair color x dietary Se level interaction (P < 0.05) occurred, in which hair Se concentration was higher in dark- than in white-colored pigs and increased as dietary Se level increased as the experiment progressed. The correlation coefficient between dietary Se level and hair Se concentration averaged 0.90 (P < 0.01). Cysteine was the amino acid in the highest concentration in hair, but this and other amino acids were not affected by Se level, Se source, or hair color. A second experiment was a 3 x 6 factorial arrangement in a split-plot design with three 9-mo-old gilts from each of the Yorkshire, Duroc, and Hampshire breeds to determine whether hair Se concentration differed by body location and breed. Hair samples were collected from the shoulder, back, rump, front-leg, belly, and hind-leg areas. Hair Se concentration was higher in red- and white-haired pigs and lower in black-haired gilts (P < 0.01). Higher hair Se concentrations (P < 0.05) occurred from the lower than from the upper body areas. Our results suggest that selenosis occurs at dietary levels > 5 ppm and that white-haired pigs exhibit alopecia sooner than dark-haired pigs. No difference in hair Se concentration occurred when diets were < 1 ppm Se, but as dietary Se level increased dark-haired pigs retained more Se in their hair than white-haired pigs.