Disrupted phylogeographical microsatellite and chloroplast DNA patterns indicate a vicariance rather than long‐distance dispersal origin for the disjunct distribution of the Chilean endemic Dioscorea biloba (Dioscoreaceae) around the Atacama Desert

Aim The Chilean endemic Dioscorea biloba (Dioscoreaceae) is a dioecious geophyte that shows a remarkable 600 km north–south disjunction in the peripheral arid area of the Atacama Desert. Its restricted present‐day distribution and probable Neogene origin indicate that its populations have a history linked to that of the Atacama Desert, making this an ideal model species with which to investigate the biogeography of the region. Location Chile, Atacama Desert and peripheral arid area. Methods Two hundred and seventy‐five individuals from nine populations were genotyped for seven nuclear microsatellite loci, and plastid trnL–F and trnT–L sequences were obtained for a representative subset of these. Analyses included the estimation of genetic diversity and population structure through clustering, Bayesian and analysis of molecular variance analyses, and statistical parsimony networks of chloroplast haplotypes. Isolation by distance was tested against alternative dispersal hypotheses. Results Microsatellite markers revealed moderate to high levels of genetic diversity within populations, with those from the southern Limarí Valley showing the highest values and northern populations showing less exclusive alleles. Bayesian analysis of microsatellite data identified three genetic groups that corresponded to geographical ranges. Chloroplast phylogeography revealed no haplotypes shared between northern and southern ranges, and little haplotype sharing between the two neighbouring southern valleys. Dispersal models suggested the presence of extinct hypothetical populations between the southern and northern ranges. Main conclusions Our results are consistent with prolonged isolation of the northern and southern groups, mediated by the life‐history traits of the species. Significant isolation was revealed at both large and moderate distances as gene flow was not evident even between neighbouring valleys. Bayesian analyses of microsatellite and chloroplast haplotype diversity identified the southern area of Limarí as the probable area of origin of the species. Our data do not support recent dispersal of D. biloba from the southern range into Antofagasta, but indicate the fragmentation of an earlier wider range, concomitant with the Pliocene–Pleistocene climatic oscillations, with subsequent extinctions of the Atacama Desert populations and the divergence of the peripheral ones as a consequence of genetic drift.     

Phenolics of five yam (dioscorea) species

Cyanidin-3-glucoside, (+)-catechin and the procyanidin dimers ‘B-1’ and ‘B-3’ were identified as phenolic constituents of Dioscorea alata tubers, and strong evidence for the presence of a procyanidin trimer and a tetramer was found. The quantity of (+)-catechin and relative proportions of the procyanidin dimers were determined in 10 cultivars of five of the main edible yam species.     

Hormonal effects on diosgenin biosynthesis and growth in Dioscorea deltoidea tissue cultures

Analysis of Dioscorea deltoidea tissue cultures grown in the presence of 2,4-D, indole-3-butyric acid, isopentenyladenine, benzyladenine and GA singly and in combination showed that the medium with 2,4-D most consistently favored diosgenin production. GA and high benzyladenine concentrations were toxic.     

Gibberellic acid-induced prolongation of the dormancy in tubers or rhizomes of several species of East Asian Dioscorea

Effects of the application of gibberellic acid on sprouting of tubers or rhizomes were tested in seven species of the genus Dioscorea that are native to the temperate regions of East Asia. The lowest concentrations for significant inhibition of sprouting in these species varied from 0.1–1 µM Application of gibberellic acid at 100 µM inhibited sprouting for more than 500 days at 20 °C. Some responses to the application of gibberellic acid differed between species and between sections of the genus. In D. japonica, the application of gibberellic acid inhibited sprouting of tubers and bulbils while it promoted seed germination.     

Wild yams revisited: Is independence from agriculture possible for rain forest hunter-gatherers?

The hypothesis that energy-rich wild plant foods are too scarce in rain forest to allow subsistence by foraging peoples independently of agriculture lacks a firm empirical basis. Data on availability of wild plant foods such as wild yams are sorely lacking, and where quantitative information is provided to support the hypothesis, it usually concerns extent of use of wild plant foods: low availability is tacitly inferred from low use. We explore the alternative hypothesis that extent of use underestimates availability of wild yams and other wild plant foods; these foods are present in large enough quantities to support hunter-gatherers, but have become increasingly neglected with increasing availability of cultivated plant foods. Thus, the subsistence of contemporary rain forest foraging peoples, in which extensive relationships with sedentary farmers appear to be universal, may be a somewhat distorted reflection of their subsistence in the pre-agricultural past. Drawing on data from ecology, archeology, ethnohistory, and linguistics, we argue that pygmy foraging peoples of the western Congo basin were present in rain forest environments before the advent of farming villagers.     

Pathogenicity of Pratylenchus coffeae,Scutellonema bradys,Meloidogyne incognita,and Rotylenchus reniformis on Dioscorea rotundata

Low populations (200 specimens per plant) of Pratylenchus cofl''eae, Scutellonema bradys, Meloidogyne incognita, and Rotylenchulus reniformis stimulated the development of tops, roots, and tubers of Dioscorea rotundata "Guinea" yam. We demonstrated experimentally that P. coffeae was responsible for the deterioration in quality of the yam tuber in Puerto Rico, a condition known as a dry rot of yam. Initial populations of 600 P. coffeae, S. bradys, or M. incognita, and populations of 1,000 P. coffeae or S. bradys per plant were high enough to induce dry rot of the yam tubers. P. coffeae and S. bradys were pathogenic to yam cultivar Guinea, but M. incognita and R. reniformis did not cause necrosis or cracking of the tuber cortex in our experiments.     

Bacterial leaf symbiosis in Dioscorea sansibarensis: morphology and ultrastructure of the acuminate leaf glands*

Abstract The symbiosis between a bacterium and the West African rain forest yam Dioscorea sansibarensis is described for the first time at the ultrastructural level. The bacteria are harboured in glands which run the entire length of the pronounced ‘drip-tip’ leaf acumenae of the host plant. Each acumen, which may be up to 12 cm long in very large mature leaves, contains from two to six bacterial glands. The glands are kidney-shaped in cross section and contain numerous multicellular simple trichomes which arise from the epidermis of the gland floor and project into the lumen of the gland. The bacteria are Gram-negative and variously rod, ovoid, and coccoid in shape. The bacterial cells contain mesosomes, polyhydroxybutyrate granules and large electron-dense bodies. Bacteria-free plants grow more slowly and produce one yellowish-green leaf per node in contrast to the vigorous growth habit of infected plants, with two deep green leaves per node. Infected plants exposed to a variety of atmospheres containing acetylene, both in the light and in the dark, failed to reduce acetylene to ethylene, indicating that nitrogen fixation is not a function of this symbiosis.     

Aboriginal Resource Utilization and Fire Management Practice in Western Arnhem Land, Monsoonal Northern Australia: Notes for Prehistory, Lessons for the Future

This paper considers traditional resources and fire management practices of Aboriginal people living in a near-coastal region of western Arnhem Land, monsoonal northern Australia. The data illustrate that before the arrival of Europeans freshwater floodplains and riverine habitats provided the major proportion of food resources over much of the seasonal cycle. By contrast, the extensive lowland woodlands and open forests, the sparser vegetation of the Arnhem Land escarpment and plateau, and the generally small patches of rain forest (jungle), provided relatively few resources, although jungle yams were of critical importance through the relatively lean wet season. The paper then considers burning as a management tool through the seasonal cycle. In broad terms, burning commenced in the early dry season and was applied systematically and purposefully over the landscape. Burning in the late dry season was undertaken with care, and resumed in earnest with the onset of the first storms of the new wet season, particularly on floodplains. These general patterns of resource use and fire management are shown to have applied widely over much of near-coastal northern Australia. The implications of these data for prehistory and for contemporary land management practices in the region, are considered. It is suggested that pre-European patterns of fire management in the region are likely to have been practiced only over the past few thousand years, given the development of abundant food resources in the late Holocene. It is shown that traditional burning practice offers a generally useful, conservative model for living in and managing a highly fire-prone savanna environment.     

The occurrence of batatasins in the dioscoreaceae

The tubers and/or aerial bulbils of 13 species of Dioscorea, mostly of tropical origin, and one species each of Rajania and Tamus, were examined for the presence of batatasins. These phenolics have previously been reported in the temperate species D. opposite. One or more batatasins were found in either tubers or bulbils of most species examined, including taxa from both Old and New Worlds, and with annual or perennial tubers. Batatasin I was the most widespread in occurrence, followed by B-II, while B-III, B-IV and B-V were comparatively rare. Only the buibils of D. opposite contained all five batatasins.