BROWN ROOT ROT OF TOMATOES

Tomato roots with brown root rot showed three types of lesion: cortical rot of fine roots, 'corky root', and basal stem rot. The fungi most commonly isocated from diseased roots were: Colletotrichum atramentarium, Chaetomium spp., Cephalosporium spp., Volutella ciliata , and a grey mycelial fungus sometimes producing pycnidia ( Pyrenochaeta sp.). Other fungi isocated less frequently were: Myrothecium roridum, Petriella asymmetrica, Trichoderma airide, Phytophthora spp., Alternaria sp. and Fusarium spp. There were differences between the numbers of each species isocated from the three types of lesion in steamed and in unsteamed soils, and some seasonal variation.
Inoculation experiments with seedlings in vitro showed that Ckaetomium cochliodes and Petriella asymmetrica could infect radicles. On older plants growing in soil Colletotrichum atramentarium was the only effective pathogen. Culture filtrates from C. atramentarium, Chaetomium cochliodes , and P. asymmetrica decreased root growth when tested in vitro. Leachates from loam and a loam-manure mixture decreased the growth of tomato root-tip cultures; the effect of these leachates was altered by autoclaving.     

Experimental and Analytical Studies of Pteridophytes XXXVI. Further Experiments on the Developmental Potentialities of Leaf Primordia in Dryopteris aristata Druce

The curve of growth in area of Pelargonium leaves against timeis strongly asymmetrical, and cannot be fitted by the usuallogistic curve. It is shown that the Gompertz curve providesan excellent fit, and the significance of its parameters isdiscussed.     

INVESTIGATIONS ON RESISTANCE TO DISEASE AMONG SPECIES OF THE GENUS AVENA

Fifty-three samples representing species of the genus Arena were tested for resistance to infection by Ustilago avenae and U. kolleri following artificial inoculation. Among the diploid and tetraploid species tested, eleven out of thirty-seven samples of Arena strigosa subsp. strigosa showed complete resistance to all the cultures with which they were inoculated. Avena strigosa subsp. barbata (three samples), and Avena strigosa subsp. abyssinica (one sample), also proved to be resistant to all the available races.
Variation in morphological and physiological characteristics within species and samples (varieties?) of the lower chromosome groups of Avena were observed and its consequences in breeding and race identification discussed.
Race identification was carried out on the eight Ustilago cultures and the existence of at least six races established. The tester varieties used in the present study proved inadequate for the complete separation of the smut races.     

A method of assessing seabird vulnerability to surface pollutants

Substantial information on the offshore distribution of seabirds exists for the North Sea and nearby areas. This information is extensive but is not easily applicable to management problems, such as oil pollution incidents. A quantitative oil vulnerability index has been developed, based on four easily scored factors, to assess the vulnerability of seabird species to surface pollution. The index has been applied to calculate area vulnerability scores for 15' latitude x 30' longitude rectangles in the North Sea by combining the species vulnerability scores with information on seabird densities. Maps of vulnerable concentrations of seabirds for each month of the year have been published with interpretative text. These maps can be used as a management tool, for example, in assessing potential risk or in the event of an oil pollution incident.     

Fire weather risk differs across rain forest—savanna boundaries in the humid tropics of north‐eastern Australia

Alternative stable state theory has been applied to understanding the control by landscape fire activity of pyrophobic tropical rain forest and pyrophytic eucalypt savanna boundaries, which are often separated by tall eucalypt forests. We evaluate the microclimate of three vegetation types across an elevational gradient and their relative fire risk as measured by McArthur's Forest Fire Danger Index (FFDI). Microclimatic data were collected from rain forest, tall eucalypt forest and savanna sites on eight vegetation boundaries throughout the humid tropics in north Queensland over a 3‐year period and were compared with data from a nearby meteorological station. There was a clear annual pattern in daily FFDI with highest values in the austral winter dry season and lowest values in the austral summer wet season. There was a strong association of the meteorological station FFDI values with those from the three vegetation types, albeit they were substantially lower. The rank order of FFDI values among the vegetation types decreased from savanna, tall eucalypt forest, then rain forest, a pattern that was consistent across each transect. Only very rarely would rain forest be flammable, despite being adjacent to highly flammable savannas. These results demonstrate the very strong effect of vegetation type on microclimate and fire risk, compared with the weak effect of elevation, consistent with a fire–vegetation feedback. This study is the first demonstration of how vegetation type influences microclimate and fire risk across a topographically complex tropical forest–savanna gradient.