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Clubroot (Plasmodiophora brassicae Woronin): an agricultural and biological challenge worldwide
Clubroot disease and the causal microbe Plasmodiophora brassicae offer abundant challenges to agriculturists and biological scientists. This microbe is well fitted for the environments which it inhabits. Plasmodiophora brassicae exists in soil as microscopic well protected resting spores and then grows actively and reproduces while shielded inside the roots of host plants. The pathogen is active outside the host for only short periods. Consequently, scientific studies are made challenging by the biological context of the host and pathogen and the technology required to investigate and understand that relationship. Controlling clubroot disease is a challenge for farmers, crop consultants and plant pathology practitioners because of the limited options which are available. Full symptom expression happens solely in members of the Brassicaceae family. Currently, only a few genes expressing strong resistance to P. brassicae are known and readily available. Agrochemical control is similarly limited by difficulties in molecule formulation which combines efficacy with environmental acceptability. Manipulation of husbandry encouraging improvements in soil structure, texture, nutrient composition and moisture content can reduce populations of P. brassicae. Integrating such strategies with rotation and crop management will reduce but not eliminate this disease. There are indications that forms of biological competition may be mobilised as additions to integrated control strategies. The aim of this review is to chart key themes in the development of scientific biological understanding of this host-pathogen relationship by offering signposts to grapple with clubroot disease which devastates crops and their profitability. Particular attention is given to the link between soil and nutrient chemistry and activity of this microbe
Ultrastructure of conidium and disjunctor development in the plant pathogenic fungus Monilinia vaccinii-corymbosi
Reproductive success of female leopards Panthera pardus: The importance of top-down processes
Long-term studies on large felids are rare and yet they yield data essential to understanding the behaviour of species and the factors that facilitate their conservation. We used the most extensive data set so far compiled on leopards Panthera pardus to establish baseline reproductive parameters for females and to determine the demographic and environmental factors that affect their lifetime reproductive success. We used comprehensive sightings reports and photographs from ecotourism lodges in the Sabi Sand Game Reserve, South Africa, to reconstruct life histories for 44 female leopards that gave birth to 172 litters over a 32-year period. Leopards appeared to exhibit a birth pulse; most litters were born in the wet season, particularly in December. Mean age at first parturition (n=26, mean±standard error=46±2 months, range=33-62) was older than previously recorded, possibly due to elevated intraspecific competition. Average litter size was 1.9±0.1 (n=140, range=1-3) and declined with maternal age. Age of litters at independence (n=52, 19±1 months, range=9-31) was inversely related to prey abundance but did not affect the likelihood of recruitment of offspring. Interbirth intervals differed following successful litters (in which at least one cub survived to independence; n=55, 25±1 months, range=14-39) and unsuccessful litters (n=46, 11±1 months, range=4-36), as did the time taken to replace litters. Variation in lifetime reproductive success was influenced mainly by differences in cub survival, which was related to maternal age and vulnerability to infanticide. Cub survival (37%) declined as females got older, perhaps because mothers relinquished portions of their home ranges to philopatric daughters. Male leopards were responsible for many (40%) cub deaths and females appeared to adopt severalstrategies to counter the risk of infanticide, including paternity confusion and displaying a period of reduced fertility immediately after a resident male was replaced. Our results suggest that the reproductive success of female leopards is regulated primarily by top-down processes. This should be taken into account in management decisions, particularly when managers are considering the implementation of invasive activities such as legal trophy hunting. © 2012 The Authors. Mammal Review © 2012 John Wiley and Sons Ltd and The Mammal Society
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