The effects of photoperiod (8, 12 or 16 h), mineral medium strength (dilutions of a tuberization medium, the T medium), sucrose (0, 2, 4, 8% w/v) and kinetin (0, 2.5 #M) on the development of roots, shoots and microtubers in shoot cultures of Dioseorea alata L. and D. bulbifera L. yams were evaluated. All. of the factors were found to have substantial effects on microtuber induction in these two species. The effects of high and low inorganic ammonium containing media on microtuberization of yam shoot cultures indicated that ammonium ions inhibited microtuber induction in D. alata but not in D. bulbifera. Microtubers ofD. alata were only formed on shoot cultures if these were held under 8-h days. D. bulbifera cultures on the other hand produced microtubers under this photoperiod treatment as well as under 16-h photoperiods provided that kinetin was present in media at 2.5/tM. Most microtuberization in D. alata shoot cultures occurred on full-strength T medium supplemented with 2% sucrose, 2.5/~M kinetin held under 8-h photoperiods at 25 °C, whereas most microtuberization in D. bulbifera shoot cultures occurred on full-strength MS medium supplemented with 4% sucrose, 2.5 ~M kinetin held under 8-h photoperiods at 25 °C. Under these two sets of conditions, yam shoot cultures consistently produced microtubers with individual weights in excess of 100 mg which were large enough to be capable of direct planting and subsequent growth in unsterilized soils.

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The publication of the Global Competitiveness Report 2005-2006 by the World Economic Forum (WEF) (2005) has focused attention once more upon the relative abilities of many countries to compete in world markets. This article provides an analysis and evaluation of the approach taken by the WEF in constructing its measure of international growth competitiveness, the Growth Competitiveness Index (GCI) which is used to rank countries. In particular, the study identifies three areas where the GCI is vulnerable to criticism. First, the treatment of outliers for hard data items is ambiguous and we identify alternative methods for dealing with outliers that are justifiable or even superior. Second, the crucial role of the variable utility patents in the calculation of the GCI is questioned and serious doubts concerning the use of this variable are raised. Third, the article suggests an alternative approach, based upon structural equation modeling, which should be used for the determination of weights in the index calculation process, rather than the arbitrary method adopted by the WEF.World Economic Forum, Growth Competitiveness Index, structural equation modeling, international growth competitiveness,

The host range of beet necrotic yellow vein virus (BNYVV) and Polymyxa betae was determined by growing plants in naturally infested soils from rhizomania outbreaks in England. Apart from Beta vulgaris, plant species infected by BNYVV were included in the families Chenopodiaceae (Atriplex patula, Chenopodium bonus‐henricus, C. hybridum, C. polyspermum and Spinacia oleracea), Amaranthaceae (Amaranthus retroflexus) and Caryophyllaceae (Silene alba, S. vulgaris, S. noctiflora and Stellaria graminea). Only P. betae isolates from B. vulgaris, C. polyspermum and S. oleracea were found to be able to transmit BNYVV back to sugar beet. When a range of weed plants from infected fields were tested, none were found to be infected by BNYVV. Therefore, it seems likely that the weed hosts play only a minor role in the spread of rhizomania disease compared to that of sugar beet, other Beta vulgaris crop types or spinach.