Search

At elevated partial pressure of CO 2 (60 Pa pCO 2 ), field-grown perennial ryegrass (Lolium perenne L.) swards generally show a strong increase in photosynthesis of the youngest fully expanded leaves but a weak yield response. We investigated this discrepancy by determining the effects of elevated pCO 2 on the dynamics of regrowth. During the whole regrowth period, swards at elevated pCO 2 exhibited a greater dry mass of roots (68%), of pseudostems (34%), and of shoot necromass below cutting height (45%). During the first 4 wk of regrowth, when dry mass (DM) and the leaf area index increased strongly, elevated pCO 2 stimulated the yield, total DM, and leaf area by up to 46, 63, and 30%, respectively. Elevated pCO 2 also resulted in an increase of almost 60% in the number of tillers during this period when the transmission of photosynthetically active radiation to the tiller bases was high. Towards the end of regrowth, however, the leaf area, total DM, and yield showed no net increase; under elevated pCO 2 , the number of tillers decreased strongly. These results indicate that there was not a strong sink for additionally fixed C during the second half of regrowth. The gap between leaf photosynthesis and yield at elevated pCO 2 is suggested to be related to a loss of tillers when shading of tiller bases was strong and to a change in dry mass allocation.

The application of biotechnology to forage grass has the potential to complement and speed up conventional breeding. To ascertain the suitability of regenerants for improvement programs, primary regenerants of tall fescue (Festuca arundinacea Schreb.) cv Tacuabe and their progenies were investigated in a field experiment located in Eschikon near Zurich (Switzerland). Thereby, the following two aspects were focused on. First, do regenerated plants and their progenies perform similar to seed-grown plants; and second, do different regeneration systems have an effect on the performance of the regenerants ? Two sets of plants, regenerated from different single-genotype derived embryogenic suspension cultures (ESC) of tall fescue, were evaluated for agronomic traits in a replicated field experiment for three growing seasons. Embryogenic suspension cultures were either routinely subcultured or cryopreserved and re-established. Seed from the primary regenerated and seed-grown plants were harvested to evaluate morphological and phenological traits of corresponding half-sib progenies in a further field experiment. When compared with seed-grown plants of the same cultivar, primary regenerants showed reduced vegetative growth and fertility. The performance of plants regenerated from cryopreserved-reestablished ESC was not inferior to corresponding plants regenerated from routinely subcultured ESC. The performance of progenies of regenerated plants did not differ from those of seed-grown plants and was within the range of the cultivar. There was no effect of the regeneration system on the performance of corresponding progenies; thus, suggesting that the weak growth of the primary regenerants was most likely of epigenetic origin. Therefore regenerated plants can be integrated into breeding programs without major restrictions.

The introduction of resistance genes from wild relatives into wheat (Triticum aestivum L.) may have detrimental effects on yield. In earlier experiments, we observed a 12% yield reduction in leaf rust (Puccinia recondita Rob. ex Desm. f. sp. tritici) resistant near isogenic lines (NIL) carrying the resistance gene Lr9 compared with the susceptible recurrent parent Arina. The aim of this study was to find physiological mechanisms for this yield reduction. Two NIL and Arina were investigated in field experiments. In a first experiment, CO 2 exchange rate (CER), transpiration, stomatal conductance (g s ), and leaf intercellular CO 2 concentration (C i ) of the flag leaf were determined after ear emergence. In a second experiment, root activity was estimated from the beginning of stem elongation to early dough stage by the application of Rb and Sr at two soil depths. The NIL and Arina had a similar CER in the morning, but in the afternoon, CER was 7 to 20% lower for the NIL compared with Arina. Differences between the NIL and Arina were larger under dry soil conditions. The CER was closely correlated with g s and C i indicating that CO 2 uptake was restricted by g s . Roots of the NIL took up 15 to 20% less Sr at the 25- to 40-cm soil depth and 12% less Rb at 10-cm soil depth compared with Arina. The reduced Sr and Rb uptake indicated less root activity for the NIL. It is concluded that lower root activity in the resistant NIL led to water stress and reduced CO 2 assimilation. Such stress periods may reduce grain number and grain size of the rust resistant NIL.

(...)Under both CO 2 treatments Genotype D accumulated substantially higher fructan concentrations than Kolibri.(...) There was a positive relationship between sucrose concentration and in vivo sucrose:sucrose fructosyltransferase (SST) activity, suggesting that sucrose induced SST activity; however, Kolibri exhibited a much lower SST activity at given sucrose concentration. Thus, the low fructan synthesis of Kolibri is associated with an initial lower sucrose concentration and with a less effective activation of SST by sucrose

The TNC accumulated in the stem up to maturity, suggesting that grain growth was restricted by factors other than assimilates. It is concluded that the ability to increase grain weight under a high assimilate supply differs between spring wheat genotypes. In short genotypes, grain growth was less restricted as compared with the tall genotypes. Grain growth in tall genotypes was not limited by lack of assimilates during floret development or early grain growth

Carbohydrate reserves are necessary for survival of perennial plants, but excess accumulation at the expense of harvestable new growth may interfere with the agronomic goal of maximizing herbage yields. The objective of this research was to examine the response of reserve carbohydrate storage and dry matter partitioning in white clover (Trifolium repens L.) to low temperature and short photoperiod. Spaced plants of two altitudinal ecotypes were grown in growth chambers at day/night temperatures and photoperiods of 18°/13°C, 16 h; 10°/7°C, 16 h; and 10°/7°C, 12 h. Plants grown under the lower temperature regime showed an increase in stolon diameter (+33% on average) and thus established a greater stolon volume (+53%) unit leaf area. Shortening the photoperiod resulted in a marked decrease in length of stolon internodes (−54%) and leaf size (−29%), but favored stolon branching (+ 23%). Low temperature depressed net assimilation rate (NAR) to a lesser extent (−38%) than rate of leaf appearance (−52%). Increased photosynthate availability under low temperature was expressed in higher total nonstructural carbohydrate (TNC) content of the leaves (+ 63%), and enabled a greater accumulation of TNC in stolons and roots (+48%). A shorter photoperiod caused a marked decrease TNC content of the leaves (−78%), but only slightly depressed reserve accumulation in stolons and roots (−14%). The alpine ecotype allocated a higher proportion of dry matter to the stolons (+ 35%) than did the valley type, which showed higher root weight proportions (+23%). It is concluded that ecotype and environment influence photosynthate partitioning by affecting plant morphology, by changing the ratio of photosynthate supply to demand, and by controlling carbohydrate use. Low temperature, short photoperiod, and alpine origin favor carbohydrate reserve storage, and thus improve prerequisites for winter survival in white clover.