Pecan nut germination — A review for the nursery industry

The shell of the pecan nut is freely permeable to water and gases, but retards germination by mechanically restricting growth of the radicle. This mechanical effect, which is pronounced at 20°C, can be overcome by germinating nuts between 30° and 35°C. Cool, moist stratification can substitute for the high-temperature germination-requirement in that following stratification nuts germinate equally well at 20°, 25° and 30°C. During stratification or incubation at high temperature, cytokinin and gibberellin levels increase in the embryo. This increase in endogenous promoter levels is closely correlated with the digestion of food reserves necessary for the resumption of embryo growth.     

The effect of DD and dazomet treatments on nematode populations at various depths in the soil and on the transmission of soil-borne tobacco rattle virus to gladiolus

The relation between log dosage of DD injected at 15 cm depth or of dazomet applied to the soil surface (all in November 1971) and probit mortality ofRotylenchus and trichodorids in the top 20 cm of a field on sandy soil was found to be linear. Dosage increase efficiencies of both chemicals against both nematode species were medium to high. Superficial application of dazomet was very effective against the nematodes that would have survived if only a low dosage of DD had been injected at 15 cm depth. Injection of 40 ml or 80 ml DD per m² at 15 cm depth killed all nematodes between 20 cm and 60 cm deep. Gladiolus planted in the spring of 1972 grew better, flowered earlier and produced more weight of corms on treated than on untreated plots. The poor growth on the untreated plots cannot be ascribed to direct damage by nematodes or to the effect of TRV transmitted to the plants by the viruliferous trichodorids occurring in these plots in high densities. Symptoms of TRV infection in plants grown in 1973 from the corms harvested in the 1972 experimental field showed that only DD treatments had reduced the rate of TRV transmission considerably. However, even the highest dosages of DD had only reduced it from 26% (on untreated plots) to about 8%. Most probably, this residual TRV infection was due to transmission by trichodorids that had survived in soil layers below 60 cm depth. Therefore, soil treatment with nematicides, cannot prevent TRV transmission to gladiolus sufficiently where viruliferous trichodorids occur at great depths, as is the case in many sandy soils having a low water table.     

Variability of some plant species from different origins and their suitability for virus work

Plants of four species obtained from various sources were raised and compared for their suitability as test plants for a number of viruses. The species comprisedChenopodium amaranticolor (local lesion host of red clover mottle virus),Nicotiana glutinosa (local lesion host of tobacco mosaic virus (TMV)),N. rustica (systemic host of TMV, cucumber mosaic virus and tomato spotted wilt virus) andN. tabacum ‘White Burley’ (systemic host of TMV). Some sources proved to be more attractive as test plants or experimental hosts because of, e.g., production of more local lesions per unit of leaf area (C. amaranticolor andN. glutinosa), distinctness of lesions (C. amaranticolor), development of more pronounced systemic symptoms (N. rustica andN. tabacum ‘White Burley’), better growth characteristics (particularlyC. amaranticolor andN. rustica), smoother leaves being easier to rub (N. glutinosa) or more and bigger leaf formation (particularlyN. rustica). The implications for the interpretation of host range studies and the quest for propagation and assays hosts are discussed.     

Severity of E. coli mastitis is mainly determined by cow factors

Intramammary infections of dairy cows with Gram-positive bacteria such as Staphylococcus aureus (major cause of mastitis) have received a lot of attention because of their major economic impact on the dairy farm through production losses induced by an increase in somatic cell count. Management strategies, including greater awareness for efficient milking and hygienic measures, have limited the spread of Gram-positive bacteria and resulted in a significant decrease of proportion of S. aureus isolates and subclinical mastitis worldwide. Other organisms such as coliform subspecies and Streptococcus uberis, both environmental bacteria that cause clinical mastitis, have received less attention. Escherichia coli causes inflammation of the mammary gland in dairy cows around parturition and during early lactation with striking local and sometimes severe systemic clinical symptoms. This disease affects many high producing cows in dairy herds and may cause several cases of death per year in the most severe cases. It is well known that bacterial, cow and environmental factors are interdependent and influence mastitis susceptibility. Many studies, executed during the last decade, indicate that the severity of E. coli mastitis is mainly determined by cow factors rather than by E. coli pathogenicity. During E. coli mastitis, the host defense status is a cardinal factor determining the outcome of the disease. Today, we know that the neutrophil is a key factor in the cows' defense against intramammary infection with E. coli. Effective elimination of the pathogen by neutrophils is important for the resolution of infection and the outcome of E. coli mastitis. This review is a compilation of some major findings over the last 15 years concerning mainly host factors that modulate and influence neutrophil function and the mammary inflammatory reaction. The individual chapters address: virulence factors of E. coli strains, how neutrophils kill E. coli, connection between endotoxins, tumor necrosis factor-alpha and nitric oxide, severity classification of E. coli mastitis, lifespan of neutrophils, host factors that influence severity, tissue damage and production loss.     

Efficiency of amino acid utilization in the growing pig at suboptimal levels of intake: branched-chain amino acids, histidine and phenylalanine + tyrosine

Five balance experiments on growing pigs were carried out to study the marginal efficiency of utilization of isoleucine, leucine, valine, histidine and phenylalanine + tyrosine and to estimate their requirements for maintenance. Purified diets based on casein and crystalline amino acids as the sole source of N contained graded levels of each amino acid, corresponding to protein accretion rates of 0, 33, 66, 99 and 132 g/day, respectively. All other essential amino acids were given in a 30% excess. N retention increased linearly (p < 0.01) as the dietary concentration of the limiting amino acid increased. Based on linear regression equations relating amino acid deposition in body protein to amino acid intake, marginal efficiencies of ileal digestible amino acid utilization were calculated to be isoleucine - 0.81, leucine - 0.81, valine - 0.82, histidine - 1.17 and phenylalanine + tyrosine - 0.67. Extrapolating the regression equations to zero N retention, the daily requirements of amino acids for N equilibrium were estimated to be (mg/kg0.75) isoleucine - 18, leucine - 33, valine - 23, histidine - 14 and phenylalanine + tyrosine - 43.