Development and evaluation of a real‐time PCR seed lot screening method for Fusarium circinatum,causal agent of pitch canker disease

Fusarium circinatum is a serious pathogen of Pinus spp. worldwide, causing pitch canker disease. F. circinatum can contaminate seeds both internally and externally and is readily disseminated via contaminated seed. Many countries require screening of pine seeds for F. circinatum before they can be imported. The currently accepted screening method is based on culturing the pathogen on a semi‐selective medium and identifying it using morphological traits. This method is time‐consuming and does not allow for accurate identification of the pathogen to the species level. A bulk DNA extraction and real‐time PCR procedure to screen seeds for the presence of F. circinatum were developed in this study. The real‐time PCR method resulted in the detection of F. circinatum in 5 of 6 commercial seed lots tested and has a lower detection limit of 1 × 10^?5 ng of F. circinatum DNA per PCR. The culture‐based method detected Fusarium spp. in four of six of the same seed lots. The real‐time PCR method can be used to screen multiple seed lots in 2 days, whereas the culture‐based method requires a minimum of 1–2 weeks. This new real‐time PCR seed screening method allows for fast, sensitive and accurate screening and can be adapted to handle larger volumes of seeds.     

The role of alkaline materials in precipitation chemistry: A brief review of the issues

The purpose of this paper is to provide a brief overview of the relatively unexplored role of alkaline materials in precipitation chemistry. Clearly, they can play fully as important a role as acidic materials in determining pH. The first major issue concerns sources. Comparison of Ca/K and Ca/Mg ratios in precipitation and dry deposition with those in likely sources indicates that both unpaved roads and soils make important contributions. Elemental emissions fluxes have been derived from literature estimates of mass emissions fluxes and element abundances in the important sources, but are subject to large uncertainties owing to a lack of adequate data. It is quite clear, however, that conventional (smokestack) sources are minor compared to open sources such as those already identified. Another major issue concerns interactions between alkaline aerosols and water in the atmosphere. Reactions involving suspended solids that lead to removal of H-ions from solution include ion exchange and mineral weathering. A simplified model of acid buffering indicates that NH4, Ca, Mg, K, and Na buffer between 25 and 50% of the potential acids in U.S. precipitation everywhere east of the Mississippi River. The third major issue concerns wet and dry deposition fluxes of alkaline materials. Wet deposition fluxes are currently being measured adequately by a nationwide network of weekly samplers. There is no agreed-upon method for monitoring dry deposition, but available information suggests that dry deposition accounts for somewhat more than half of the Ca deposition. A list of research and data needs is also provided.     

Epidemiology of wildebeest-derived malignant catarrhal fever in South Africa: inability to transfer the disease with an African face fly Musca xanthomelas (Diptera: Muscidae)

Under experimental conditions an African face fly (Musca xanthomelas) preferred to feed on cattle dung when provided with a choice of 3 different meals namely sucrose, cattle dung and blood. Flies starved overnight fed well on the eyes of cattle and rabbits, but were reluctant to feed again within 2 h after being allowed to feed on cell culture medium or on the eyes of wildebeest, and when they did feed, they preferred to feed on the external side of the eyelids and on the coagulated material in the medial canthus of the eye. Under field conditions flies were rarely seen to feed on the eyes of immobilized wildebeest. Although M. xanthomelas became infected with Alcelaphinae herpes virus 1 (AHV-1) when they fed on infective wildebeest tears or cell culture medium, they lost the virus within 5 h, and recovery of infective AHV-1 particles from regurgitated cell culture medium was limited to the first 30 min after feeding. AHV-1 could not be transmitted by flies to cattle or rabbits. The failure to transfer the virus with flies can be ascribed to their reluctance to feed on cattle or rabbits shortly after they have consumed a protein rich meal, the rapid inactivation of ingested virus and the relatively high titre of virus necessary to infect cattle via the ocular route. Furthermore, it is believed that under natural conditions flies that have emerged from cattle dung will be inclined to stay with cattle where food is freely available.(ABSTRACT TRUNCATED AT 250 WORDS)     

A simple technique for the rapid diagnosis of rabies in formalin-preserved brain

A simple technique is described for the rapid diagnosis of rabies in formalin-preserved brain. Brain tissue was emulsified, washed with phosphate-buffered saline and digested with trypsin. The digested material was stained according to conventional immunofluorescent procedures. Digestion with trypsin markedly enhanced the staining of rabies inclusions and eliminated non-specific staining of formalin-preserved brain. The method seems to be more accurate than histological examination.     

Bluetongue virus as a cause of hydranencephaly in cattle.

Hydranencephaly was produced in a foetus and a calf by intra-uterine infection with an attenuated Type 10 bluetongue virus. Laparotomy was performed on the respective dams and the foetuses, respectively 126 days and 138 days old, were inoculated intramuscularly through the uterine wall with 1 ml of a virus suspension containing 5 x 103 tissue culture infective doese. The younger feotus was aborted on Day 262, while the other one was born alive on Day 273. Both foetuses showed marked hydranencephaly.     

Forage production of some grass species in the false Thornveld of the Eastern Cape

Abstract

The most commonly occurring grass species in the False Thornveld (Acocks, 1953; veld type no. 21) were clipped before and after grazing on veld in good and poor condition at different times of the year. Herbage yield per species was expressed per unit basal tuft area, and the difference in yield before and after grazing was considered to reflect the production of available forage. Themeda triandra produced more forage than any other species at all times of the year. Sporobolus fimbriatus generally produced the second highest amount of available forage. Cymbopogon plurinodis, despite having the second highest herbage yield before grazing, was not grazed to a significant extent. On the basis of the results, Themeda triandra and Sporobolus fimbriatus were identified as key grass species in the False Thornveld of the Eastern Cape.     

The influence of an Acacia karroo tree on grass production in its vicinity

Abstract

The investigation was concerned with the impact of an Acacia karroo tree on the productivity of the surrounding herbaceous layer.

It was established that a consistent pattern of grass production occurs around isolated A. karroo trees. This is characterized by high yields under and immediately south of the tree canopy, and low yields immediately to the north of the canopy. The former is attributed to favourable influences by the tree (e.g. shade and tree leaf litter), whereas the latter is probably a result of reduced water input associated with physical redistribution of rainfall by the tree and competition from the tree for soil water.

It is argued that the net effect of the favourable or unfavourable influences of A. karroo on grass production is dependent on tree density. This explains why grass production is greater where there are a few A. karoo trees than where there are no trees and why grass production declines as tree density increases beyond a critical level.