Ultrastructural studies of the infection of susceptible and resistant cultivars of Sorghum bicolor by Colletotrichum sublineolum were conducted. Initial penetration events were the same on both susceptible and resistant cultivars. Germ tubes originating from germinated conidia formed globose, melanized appressoria, that penetrated host epidermal cells directly. Appressoria did not produce appressorial cones, but each penetration pore was surrounded by an annular wall thickening. Inward deformation of the cuticle and localized changes in staining properties of the host cell wall around the infection peg suggests that penetration involves both mechanical force and enzymic dissolution. In compatible interactions, penetration was followed by formation of biotrophic globular infection vesicles in epidermal cells. Filamentous primary hyphae developed from the vesicles and went on to colonize many other host cells as an intracellular mycelium. Host cells initially survived penetration. The host plasma membrane invaginated around infection vesicles and primary hyphae and was appressed tightly to the fungal cell wall, with no detectable matrix layer at the interface. Necrotrophic secondary hyphae appeared after 66 h and ramified through host tissue both intercellularly and intracellularly, forming hypostromatic acervuli by 114 h. Production of secondary hyphae was accompanied by the appearance of electron-opaque material within infected cells. This was thought to represent the host phytoalexin response. In incompatible interactions, infection vesicles and primary hyphae were formed in epidermal cells by 42 h. However, they were encrusted with electron-opaque material and appeared dead. These observations are discussed in relation to the infection processes of other Colletotrichum spp. and the host phytoalexin response.

SUMMARYCytological and physiological studies were conducted on the infection process of Colletotrichum sublineolum P. Henn. Kabat et Bub. on susceptible and resistant cultivars of Sorghum hicolor (L.) Moench. Compatible interactions were characterized by an early biotrophic phase lasting c. 24 h, during which intracellular infection vesicles and prin-iary hyphae colonized epidermal cells. 7 hinner secondary hyphae were first observed branching out from primary hyphae after 66 h. These hyphae proliferated throughout the epidermis and into underlying mesophyll cells. Secondary hyphae were associated with host cell death and the onset of a necrotrophic phase. Pigmented cytoplasmic inclusions, thought to represent the host defence response, were also first observed at 66 h, although there was little apparent effect on subsequent fungal colonization of tissue. By 90 h, secondary hyphae had proliferated throughout the leaf sheath, with production of necrotic lesions and acervuli. In incompatible interactions, infection vesicles formed inside epidermal cells within 42 h of inoculation but there was no evidence for a biotrophic interaction as penetrated cells appeared dead and fungal developmer>t was restricted to single epidermal cells. Host defence responses were observed earlier than in compatible interactions: heavily pigmented (dark red) cytoplasmic inclusions were distributed throughout penetrated cells at 42 h. By 66 h, these cytoplasmic inclusions had disintegrated and dark red pigment had spread throughout the cell. Concurrent with the disintegration of the cytoplasmic inclusions was the disruption of the cytoplasm of both the host cell and the fungus. Further fungal development was restricted. These observations are discussed in relation to the importance of the initial biotrophic phase in the successful colonization of S. bicolor by C. sublineolum and the role of the host defence response in preventing colonization.

Summary Biodiversity is changing at unprecedented rates, and it is increasingly important that these changes are quantified through monitoring programmes. Previous recommendations for developing or enhancing these programmes focus either on the end goals, that is the intended use of the data, or on how these goals are achieved, for example through volunteer involvement in citizen science, but not both. These recommendations are rarely prioritized.We used a collaborative approach, involving 52 experts in biodiversity monitoring in the UK, to develop a list of attributes of relevance to any biodiversity monitoring programme and to order these attributes by their priority. We also ranked the attributes according to their importance in monitoring biodiversity in the UK. Experts involved included data users, funders, programme organizers and participants in data collection. They covered expertise in a wide range of taxa.We developed a final list of 25 attributes of biodiversity monitoring schemes, ordered from the most elemental (those essential for monitoring schemes; e.g. articulate the objectives and gain sufficient participants) to the most aspirational (e.g. electronic data capture in the field, reporting change annually). This ordered list is a practical framework which can be used to support the development of monitoring programmes.People's ranking of attributes revealed a difference between those who considered attributes with benefits to end users to be most important (e.g. people from governmental organizations) and those who considered attributes with greatest benefit to participants to be most important (e.g. people involved with volunteer biological recording schemes). This reveals a distinction between focussing on aims and the pragmatism in achieving those aims. Synthesis and applications. The ordered list of attributes developed in this study will assist in prioritizing resources to develop biodiversity monitoring programmes (including citizen science). The potential conflict between end users of data and participants in data collection that we discovered should be addressed by involving the diversity of stakeholders at all stages of programme development. This will maximize the chance of successfully achieving the goals of biodiversity monitoring programmes.

A 3-year study on the epidemiology of sorghum anthracnose (Colletotrichum sublineolum) and leaf blight (Exserohilum turcicum) was conducted at Alupe in western Kenya from 1994 to 1996. A nonlinear logistic model was used to summarize 72 anthracnose and 108 leaf blight disease progress curves from different planting dates and cultivars. Effects of planting date and cultivar on disease development were compared based on estimates of the rate (␤), the absolute rate (), inflection point () and upper asymptote (␥), disease severity at milk stage (v 95), and time taken to reach a disease severity of 2% (t 2 , an estimate of time when disease is first observed). Leaf blight epidemics always started earlier than those of anthracnose, but exhibited lower disease severity at crop maturity. Effects of planting date and cultivar on ␤ varied between years. Delaying planting reduced time to disease onset (i.e. and t 2) and increased absolute rate of progress , resulting in maximum severity at crop 'milk stage' and maturity (v 95 and ␥, respectively). Resistant cultivars had highest and t 2 but lowest , v 95 and ␥ values for both diseases. Delaying planting affected anthracnose progress more on the resistant cultivars, in contrast with leaf blight for which progress on susceptible cultivars was more affected. The implications of these findings for disease management are discussed, and recommendations made to improve disease screening methodologies.