Formation and Survival of Oospores of Phytophthora-Infestans Under Natural Conditions

Phytophthora infestans is able to produce oospores in leaves of potato and tomato plants after inoculation with a mixture of A1 and A2 mating-type isolates. Various conditions for oospore formation were analysed. Under controlled conditions, oospores were produced in potato leaves at temperatures ranging from 5 to 25 degrees C. In leaves of potato cultivar Bintje incubated at 15 degrees C, oogonia and antheridia were observed 6 days after inoculation and thick-walled oospores appeared 3-4 days later. In field experiments oospores were found in leaves and stems of potato cultivars Bintje, Irene and Pimpernel and in leaves, stems and fruits of tomato cultivar Moneymaker within 2 weeks after inoculation. A bioassay was developed to test the survival of oospores in soil under various conditions. To determine whether late-blight infections derived from infectious soil were caused by oospores, DNA fingerprinting was performed. DNA fingerprint probe RG-57 was suitable for distinguishing asexual progeny from recombinant progeny arising from soil-borne oospores. We demonstrated survival of viable, infectious oospores of P. infestans in soil during the winter of 1992-93. Oospores were not infectious from soil exposed to temperatures of 40 degrees C or higher but in the range 35 degrees C to as low as -80 degrees C for 48 h, oospores survived

A place for place: Modelling and analysing platial representations

This editorial presents a special collection of papers addressing the concept of place and its use in geographical information science (GIScience). The concept of place is a topic of increasing interest among GIScience scholars. First attempts to formalise platial information have been made and it is increasingly held that user‐generated data sets in particular are often more platial than spatial in nature. At the same time, and especially when compared to geometric spatial concepts, the concept of place is ambiguous, complex and difficult to capture in formal and analytical terms, suggesting the need for interdisciplinary approaches. This collection presents articles covering a wide range of place‐related aspects, including both conceptual and more applied contributions. In the present editorial we summarise these and comment on their individual contributions, and hope that the readership of Transactions in GIS will find the special collection inspiring and informative