Helianthus annuus
not annotated - annotated - LINNAEUS only
20831646
Floret initiation, tissue expansion and carbon availability at the meristem of the sunflower capitulum as affected by water or light deficits.
* The co-ordination between floret initiation and meristem expansion, and their relationships with carbon availability, were studied and quantified in sunflower (Helianthus annuus) plants subjected to light or water shortages. * Meristem size, number of floret primordia, primordium size, rate of plant biomass accumulation, leaf area, photosynthetic rate, and soluble sugar content in the capitulum were measured until completion of floret initiation. * Although treatments differentially affected tissue expansion and biomass acquisition, a common relationship between the final number of florets and the rate and duration of meristem expansion was conserved. In the absence of water deficit, changes in relative expansion rate in the meristem paralleled changes in soluble sugar content. Water deficit reduced tissue expansion both in leaves and in the capitulum, and induced the accumulation of soluble sugars in the meristem. Use of these sugars at re-watering was associated with increased meristem growth and higher floret numbers compared with control plants. * Floret initiation and meristem tissue expansion remained strongly co-ordinated under all studied circumstances, and both depended on local carbon availability when water supply was unlimited. Transient water deficits favoured reproductive meristem growth and floret production. Equations accounting for these results constitute a framework for phenotyping the response to drought.
21029117
Dynamic changes of canopy-scale mesophyll conductance to CO2 diffusion of flower as affected by CO2 concentration and abscisic acid.
Leaf-level measurements have shown that mesophyll conductance (g(m)) can vary rapidly in response to CO2 and other environmental factors, but similar studies at the canopy-scale are missing. Here, we report the effect of short-term variation of CO2 concentration on canopy-scale g(m) and other CO2 exchange parameters of sunflower (Helianthus annuus L.) stands in the presence and absence of abscisic acid (ABA) in their nutrient solution. g(m) was estimated from gas exchange and on-line carbon isotope discrimination (Delta(obs)) in a ^1^3CO2/^1^2CO2) gas exchange mesocosm. The isotopic contribution of (photo)respiration to stand-scale Delta(obs) was determined with the experimental approach of Tcherkez et al. Without ABA, short-term exposures to different CO2 concentrations (C(a) 100 to 900 mumol mol-^1) had little effect on canopy-scale g(m) . But, addition of ABA strongly altered the CO2-response: g(m) was high (approx. 0.5 mol CO2 m-^2 s-^1) at C(a) <200 mumol mol-^1 and decreased to <0.1 mol CO2 m-^2 s-^1 at C(a) >400 mumol mol-^1. In the absence of ABA, the contribution of (photo)respiration to stand-scale Delta(obs) was high at low C(a) (7.2 %) and decreased to <2 % at C(a) > 400 mumol mol-^1. Treatment with ABA halved this effect at all C(a) .
22182606
Sunflower stem weevil and its larval parasitoids in native sunflowers: is parasitoid abundance and diversity greater in the u.s. Southwest?
Classical biological control programs often target a pest's region of origin as a likely source for new biological control agents. Here, we use this approach to search for biological control agents of the sunflower stem weevil (Cylindrocopturus adspersus LeConte), an economically important pest of commercial sunflower. We conducted surveys of weevil natural enemy diversity and abundance across a transect running from the northern Great Plains to the southwestern U.S. (the presumed area of endemism of annual sunflower species in the genus Helianthus). Accordingly, natural enemy diversity and abundance were expected to be greater in the southwestern U.S. C. adspersus and their larval parasitoids were collected from stems of four native sunflower species (Helianthus annuus, H. nuttallii, H. pauciflorus, and H. petiolaris) from 147 sites across eight states. Native H. annuus constituted the majority of the sunflower populations. Mean weevil densities were significantly higher in sunflower stalks that were larger in diameter. Mean weevil densities within sites did not differ across the range of longitudes and latitudes sampled. After accounting for the effects of stalk diameter and location, weevil densities did not differ among the four sunflower species nor did they differ as a function of elevation. C. adspersus in H. annuus and H. petiolaris were attacked by seven species of parasitoids. No parasitoids were found attacking C. adspersus in H. nuttallii or H. pauciflorus stalks. C. adspersus were twice as likely to be attacked by a parasitoid when feeding on H. petiolaris than H. annuus. Furthermore, the likelihood that C. adspersus would be parasitized decreased with increasing elevation and increasing stem diameters. All parasitoid species have been previously reported attacking C. adspersus larvae in cultivated sunflower. Species richness was less diverse in these collections than from previous studies of cultivated sunflower. Our findings suggest that the species of larval parasitoids attacking C. adspersus in native sunflowers have successfully made the transition to cultivated sunflower.