Regeneration dynamics of alluvial gaps in a warm temperate rain forest in New Zealand

Gaps formed by stream laid gravels in a warm temperate Podocarp-Angiosperm rain forest in New Zealand were quickly invaded by 41 free-standing woody species. Height-age curves for the eight most frequent species were used to construct a 12 yr chronosequence which showed 18 species arrived by 0.9 yr and 33 by 1.9 yr. This rapid invasion was supplied from both gaps and mature forest and fitted the Initial Floristic Model coupled with a Facilitation Mechanism. Over the 12 yr period, stem density and births peaked at 0.9 yr and deaths at 1.9 yr with a natality of 39.5/m², a mortality of 38.5/m² and nearly 99% dying as seedlings. Plant height increased to 5.1 m at 12.1 yr with height increment peaking at 43 cm/yr at 7.3 yr. Maximum potential heights ranged from 4 to 60 m and were positively correlated with longevity which varied from 20 to 1150 yr for 19 known species. A decline in height increment to 0.9 yr showed a below-ground component in intraspecific competition with significant negative correlations between stem density and height indicating a later above-ground component. There was no significant height competition amongst the 11 most frequent species and only one significant negative interspecific association. This suggests high species coexistence for which Equal chance was probably the major mechanism. Given this coexistence, rapid species arrival, early sexual maturity and similar density and height-age patterns, the main dynamic variables may be maximum height, longevity and height increment, all of which are, partly, genetically programmed. Most dynamic affinities are with tropical forest, although height growth and species richness are warm temperate.     

Co-limitation of potato growth by Potato Cyst Nematode (Globodera rostochiensis) and Rhizoctonia solani

Globodera rostochiensis and Rhizoctonia solani are the most important growth limiting factors influencing potato production in Iran. The effects of inoculation with Potato Cyst Nematodes (PCN) (0, 50, 75 and 100 cysts/3.5?kg soil) and R. solani (with or without inoculation) on potato growth and development were investigated in cultivars Santé and Marfona. Inoculation with R. solani induced severe damage, especially when inoculation was accompanied with high density of PCN. The damage caused by R. solani tended to increase with an increase in PCN density, especially in Marfona. In Santé, number of stems or branches per plant significantly increased by inoculation with R. solani, while in Marfona it was significantly affected either by R. solani inoculation or PCN density. In Santé, number of stolons per plant was significantly increased by PCN, but not by R. solani. In Marfona, however, the number of stolons per plant was significantly affected either by R. solani inoculation or by presence of PCN, but not affected by PCN density. The general effect of R. solani or PCN inoculation treatments on shoot, below-ground and total dry weight of potato was significant, but strongly affected by cultivar. In general, our study supports the synergistic interaction between R. solani and PCN and its moderation by the use of a resistant cultivar such as Santé.     

QTL analysis and QTL-based prediction of flowering phenology in recombinant inbred lines of barley

Combining ecophysiological modelling and genetic mapping has increasingly received attention from researchers who wish to predict complex plant or crop traits under diverse environmental conditions. The potential for using this combined approach to predict flowering time of individual genotypes in a recombinant inbred line (RIL) population of spring barley (Hordeum vulgare L.) was examined. An ecophysiological phenology model predicts preflowering duration as affected by temperature and photoperiod, based on the following four input traits: f(o) (the minimum number of days to flowering at the optimum temperature and photoperiod), theta1 and theta2 (the development stages for the start and the end of the photoperiod-sensitive phase, respectively), and delta (the photoperiod sensitivity). The model-input trait values were obtained from a photoperiod-controlled greenhouse experiment. Assuming additivity of QTL effects, a multiple QTL model was fitted for the model-input traits using composite interval mapping. Four to seven QTL were identified for each trait. Each trait had at least one QTL specific to that trait alone. Other QTL were shared by two or all traits. Values of the model-input traits predicted for the RILs from the QTL model were fed back into the ecophysiological model. This QTL-based ecophysiological model was subsequently used to predict preflowering duration (d) for eight field trial environments. The model accounted for 72% of the observed variation among 94 RILs and 94% of the variation among the two parents across the eight environments, when observations in different environments were pooled. However, due to the low percentage (34-41%) of phenotypic variation accounted for by the identified QTL for three model-input traits (theta1, theta2 and delta), the QTL-based model accounted for somewhat less variation among the RILs than the model using original phenotypic input trait values. Nevertheless, days to flowering as predicted from the QTL-based ecophysiological model were highly correlated with days to flowering as predicted from QTL-models per environment for days to flowering per se. The ecophysiological phenology model was thus capable of extrapolating (QTL) information from one environment to another.     

Pollen germination and in vivo fertilization in response to high‐temperature during flowering in hybrid and inbred rice

High‐temperature during flowering in rice causes spikelet sterility and is a major threat to rice productivity in tropical and subtropical regions, where hybrid rice development is increasingly contributing to sustain food security. However, the sensitivity of hybrids to increasing temperature and physiological responses in terms of dynamic fertilization processes is unknown. To address these questions, several promising hybrids and inbreds were exposed to control temperature and high day‐time temperature (HDT) in Experiment 1, and hybrids having contrasting heat tolerance were selected for Experiment 2 for further physiological investigation under HDT and high‐night‐time‐temperature treatments. The day‐time temperature played a dominant role in determining spikelet fertility compared with the night‐time temperature. HDT significantly induced spikelet sterility in tested hybrids, and hybrids had higher heat susceptibility than the high‐yielding inbred varieties. Poor pollen germination was strongly associated with sterility under high‐temperature. Our novel observations capturing the series of dynamic fertilization processes demonstrated that pollen tubes not reaching the viable embryo sac was the major cause for spikelet sterility under heat exposure. Our findings highlight the urgent need to improve heat tolerance in hybrids and incorporating early‐morning flowering as a promising trait for mitigating HDT stress impact at flowering.     

Tuber induction and initiation during production and early field growth of transplants from in vitro-derived potato plants

In transplants from in vitro‐derived plantlets from very early potato (Solanum tuberosum) cultivars, a lower degree of tuber induction at the time of field planting is thought to increase tuber production. Leaf‐bud cuttings were used to assess the progress to tuber induction in in vitro‐derived potato plantlets during the transplant production phase and after subsequent transplanting into the field. Induction and initiation of tubers on the same plants were assessed to study the effects of the duration of transplant production and conditions during transplant production for cv. Gloria (very early) and cv. Bintje (mid‐early). In vitro‐produced plantlets were not induced by the time of planting but rapidly progressed to the induced state thereafter. The progress in induction with time and the change in percentage of plants showing tubers fitted typical sigmoid curves. Plantlets achieved 50% induction ca 15 days after planting into in vivo conditions, and 50% tuber initiation usually occurred 10 days later. Shorter transplant production periods reduced the degree of induction of the transplants at field planting. Transplant production for more than 2 weeks was required to allow conditions during that period to affect induction or initiation. Long‐term non‐inducing conditions delayed the progress to tuber induction in cv. Gloria and delayed tuber initiation in both cultivars. Cv. Gloria showed no faster progress to induction than cv. Bintje but initiated tubers earlier. The results suggest that the relation between progress to induction and tuber initiation is cultivar dependent and that leaf‐bud cuttings can be used successfully in very young in vitro‐derived plants for assessing the progress to tuber induction.     

Physical aging of dry elastin

Dry purified ligamentum nuchae elastin has been investigated for physical aging. The samples were quenched from a temperature (197°C) close to the softening point to a number of measuring temperatures ranging from ?20 to +180°C. At each temperature, the small-strain torsional creep properties were determined at a number of elapsed intervals after the quench. Aging effects were found over the whole temperature range, and the creep and aging behavior of elastin turned out to be very similar to that of synthetic polymers.     

Physiological basis of genetic variation in leaf photosynthesis among rice (Oryza sativa L.) introgression lines under drought and well-watered conditions

To understand the physiological basis of genetic variation and resulting quantitative trait loci (QTLs) for photosynthesis in a rice (Oryza sativa L.) introgression line population, 13 lines were studied under drought and well-watered conditions, at flowering and grain filling. Simultaneous gas exchange and chlorophyll fluorescence measurements were conducted at various levels of incident irradiance and ambient CO(2) to estimate parameters of a model that dissects photosynthesis into stomatal conductance (g (s)), mesophyll conductance (g (m)), electron transport capacity (J (max)), and Rubisco carboxylation capacity (V (cmax)). Significant genetic variation in these parameters was found, although drought and leaf age accounted for larger proportions of the total variation. Genetic variation in light-saturated photosynthesis and transpiration efficiency (TE) were mainly associated with variation in g (s) and g (m). One previously mapped major QTL of photosynthesis was associated with variation in g (s) and g (m), but also in J (max) and V (cmax) at flowering. Thus, g (s) and g (m), which were demonstrated in the literature to be responsible for environmental variation in photosynthesis, were found also to be associated with genetic variation in photosynthesis. Furthermore, relationships between these parameters and leaf nitrogen or dry matter per unit area, which were previously found across environmental treatments, were shown to be valid for variation across genotypes. Finally, the extent to which photosynthesis rate and TE can be improved was evaluated. Virtual ideotypes were estimated to have 17.0% higher photosynthesis and 25.1% higher TE compared with the best genotype investigated. This analysis using introgression lines highlights possibilities of improving both photosynthesis and TE within the same genetic background.     

Picosecond excitation energy transfer of allophycocyanin studied in solution and in crystals

Cyanobacteria perform photosynthesis with the use of large light-harvesting antennae called phycobilisomes (PBSs). These hemispherical PBSs contain hundreds of open-chain tetrapyrrole chromophores bound to different peptides, providing an arrangement in which excitation energy is funnelled towards the PBS core from where it can be transferred to photosystem I and/or photosystem II. In the PBS core, many allophycocyanin (APC) trimers are present, red-light-absorbing phycobiliproteins that covalently bind phycocyanobilin (PCB) chromophores. APC trimers were amongst the first light-harvesting complexes to be crystallized. APC trimers have two spectrally different PCBs per monomer, a high- and a low-energy pigment. The crystal structure of the APC trimer reveals the close distance (~21 Å) between those two chromophores (the distance within one monomer is ~51 Å) and this explains the ultrafast (~1 ps) excitation energy transfer (EET) between them. Both chromophores adopt a somewhat different structure, which is held responsible for their spectral difference. Here we used spectrally resolved picosecond fluorescence to study EET in these APC trimers both in crystallized and in solubilized form. We found that not all closely spaced pigment couples consist of a low- and a high-energy pigment. In ~10% of the cases, a couple consists of two high-energy pigments. EET to a low-energy pigment, which can spectrally be resolved, occurs on a time scale of tens of picoseconds. This transfer turns out to be three times faster in the crystal than in the solution. The spectral characteristics and the time scale of this transfer component are similar to what have been observed in the whole cells of Synechocystis sp. PCC 6803, for which it was ascribed to EET from C-phycocyanin to APC. The present results thus demonstrate that part of this transfer should probably also be ascribed to EET within APC trimers.     

Influence of Nitrogen Supply on the Susceptibility of Wheat to Septoria tritici

Nitrogen (N) fertilization is required for achieving high yields in wheat (Triticum aestivum L.) but may enhance the development of Septoria tritici Rob. ex Desm. A study was undertaken to investigate how N supply influences the area under disease progress curve (AUDPC). Two field experiments were carried out in a typical argiudol in 1996 and 1997. Six cultivars were grown at two N treatments (0 and 100–150 kg N/ha) in a split plot design. Percentage of necrosis (severity) of the two upper leaves of each treatment was evaluated three times during the growing season. Height and heading date were also scored and related to the resistance level. In 1996, with weather conditions conducive to the disease, AUDPC values were higher in the fertilized treatment. In 1997, with insufficient rain immediately after inoculation, the disease only progressed faster under N fertilization in the flag leaf, which was exposed to conducive environmental conditions from its appearance. The effect of N fertilization was influenced by the cultivar characteristics, climatic and agronomic conditions. Knowledge that N fertilization promotes the development of S. tritici in conducive conditions will be useful for deciding management strategies of the cultivars and for optimizing conditions for the selection in breeding programmes.