Chromosome studies on some Asteraceae from South America

Mitotic or meiotic chromosome numbers for 42 accessions belonging to 39 species of different genera of Asteraceae were determined. First chromosome counts are reported for one genus ( Gymnocoronis ), 14 species, and one variety. These are as follows: Solidago chilensis var. megapotamica (2 n  = 2 x  = 18), Chromolaena barbacensis (2 n  = 3 x  = 30), Chromolaena christieana (2 n  = 3 x  = 30), Chromolaena hirsuta (2 n  = 4 x  = 40), Chromolaena verbenacea ( n  = 20 II, 2 n  = 4 x  = 40), Disynaphia multicrenulata (2 n  = 2 x  = 20), Gymnocoronis spilanthoides var. subcordata (2 n  = 2 x  = 20), Mikania thapsoides (2 n  = 4 x  = 68), Stevia commixta (2 n  = 2 x  = 22), Porophyllum brevifolium (2 n  = 4 x  = 44), Viguiera rojasii (2 n  = 2 x  = 34), Pterocaulon angustifolium (2 n  = 2 x  = 20), Gochnatia haumaniana (2 n  = 4 x  = 44), Senecio ostenii (2 n  = 4 x  = 40), Senecio pinnatus (2 n  = 8 x  = 80), and Lepidaploa amambaia (2 n  = 2 x  = 28). Chromosome numbers differing from those reported previously in the literature were found in Campuloclinium macrocephalum (2 n  = 2 x  = 20), Melanthera latifolia (2 n  = 4 x  = 60), Chrysolaena flexuosa (2 n  = 2 x  = 20), and Cyrtocymura cincta (2 n  = 4 x  = 40). The relevance of the results is discussed in relation to the available data for each of the analysed taxa. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 153 , 221–230.     

Molecular phylogeny and diversification history of Prosopis (Fabaceae: Mimosoideae)

The genus Prosopis is an important member of arid and semiarid environments around the world. To study Prosopis diversification and evolution, a combined approach including molecular phylogeny, molecular dating, and character optimization analysis was applied. Phylogenetic relationships were inferred from five different molecular markers ( mat K- trn K, trn L- trn F, trn S- psb C, G3pdh, NIA). Taxon sampling involved a total of 30 Prosopis species that represented all Sections and Series and the complete geographical range of the genus. The results suggest that Prosopis is not a natural group. Molecular dating analysis indicates that the divergence between Section Strombocarpa and Section Algarobia plus Section Monilicarpa occurred in the Oligocene, contrasting with a much recent diversification (Late Miocene) within each of these groups. The diversification of the group formed by species of Series Chilenses, Pallidae, and Ruscifoliae is inferred to have started in the Pliocene, showing a high diversification rate. The moment of diversification within the major lineages of American species of Prosopis is coincident with the spreading of arid areas in the Americas, suggesting a climatic control for diversification of the group. Optimization of habitat parameters suggests an ancient occupation of arid environments by Prosopis species.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 621–640.     

Growth dynamics and genotypic variation in tropical, field-grown paddy rice (Oryza sativa L.) in response to increasing carbon dioxide and temperature

While previous studies have examined the growth and yield response of rice to continued increases in CO₂ concentration and potential increases in air temperature, little work has focused on the long-term response of tropical paddy rice (i.e. the bulk of world rice production) in situ, or genotypic differences among cultivars in response to increasing CO₂ and/or temperature. At the International Rice Research Institute, rice (cv IR72) was grown from germination until maturity for 4 field seasons, the 1994 and 1995 wet and the 1995 and 1996 dry seasons at three different CO₂ concentrations (ambient, ambient + 200 and ambient + 300 μL L^–1 CO₂) and two air temperatures (ambient and ambient + 4 °C) using open-top field chambers placed within a paddy site. Overall, enhanced levels of CO₂ alone resulted in significant increases in total biomass at maturity and increased seed yield with the relative degree of enhancement consistent over growing seasons across both temperatures. Enhanced levels of temperature alone resulted in decreases or no change in total biomass and decreased seed yield at maturity across both CO₂ levels. In general, simultaneous increases in air temperature as well as CO₂ concentration offset the stimulation of biomass and grain yield compared to the effect of CO₂ concentration alone. For either the 1995 wet and 1996 dry seasons, additional cultivars (N-22, NPT1 and NPT2) were grown in conjunction with IR72 at the same CO₂ and temperature treatments. Among the cultivars tested, N-22 showed the greatest relative response of both yield and biomass to increasing CO₂, while NPT2 showed no response and IR72 was intermediate. For all cultivars, however, the combination of increasing CO₂ concentration and air temperature resulted in reduced grain yield and declining harvest index compared to increased CO₂ alone. Data from these experiments indicate that (a) rice growth and yield can respond positively under tropical paddy conditions to elevated CO₂, but that simultaneous exposure to elevated temperature may negate the CO₂ response to grain yield; and, (b) sufficient intraspecific variation exists among cultivars for future selection of rice cultivars which may, potentially, convert greater amounts of CO₂ into harvestable yield.     

USE OF PURCHASE PREFERENCE OPTIONS TO INCREASE "NO PREFERENCE" FREQUENCIES IN PLACEBO PREFERENCE TESTS

Besides responses to the different stimuli being tested in a paired preference test, responses to identical "placebo" stimuli can be used as a screening tool to identify biased consumers. Those consumers who give preference responses to identical stimuli can be assumed to be biased. Accordingly, only the data from unbiased consumers need to be considered for the different stimuli. The problem with this procedure is that the sample size is reduced. The goal of the present research was to see whether using options associated with purchase intent, elicited a greater number of "No Preference" responses to identical "placebo" stimuli. It was found that they did. The increase was large when the preference options implied exclusivity. In conditions where the preference strength options were not so strong, the frequency of "No Preference" responses dropped accordingly.

PRACTICAL APPLICATIONS

A problem with paired preference testing is the tendency of consumers to give false preferences, which produces the seriously misleading overestimation of the proportion of consumers who have preferences for one or other of the products being assessed. The "placebo" condition is an important control for alleviating this problem. The statistical analysis can be improved by finding a protocol that maximizes the proportion of "No Preference" responses in the placebo condition. The key finding here is that using purchase intent questions rather than preference questions may possibly provide a way of achieving this aim.     

PAIRED PREFERENCE TESTS: d' VALUES FROM MEXICAN CONSUMERS WITH VARIOUS RESPONSE OPTIONS

Three groups, each comprising 200 consumers, performed paired preference tests between two flavors of potato chips. For one group, a “No Preference” option was allowed, while for the second group, it was not. For a third group, a “No Preference” option was allowed while the preference responses were differentiated as “Strong Preference” and “Weak Preference.” For all three groups, d′ values representing overall strength of preference did not differ significantly.