Physiological causes of yield variation in cassava (Manihot esculenta Crantz)

Cassava (Manihot esculenta Crantz) is an important crop in many parts of the tropics, being mainly cultivated for its storage roots. Farmers' yields are low and one of the constraints to higher yields is the lack of adequate clones. At the beginning of the 1970s an extensive cassava research programme was started at CIAT (Colombia). One of its aims was to develop high-yielding clones by genetic modification of the plant habitus.This thesis begins with a literature review in which the available information on the physiological determinants of the yield of cassava storage roots is described.Next, a series of experiments carried out to deepen and to broaden this knowledge on physiological causes of yield variation in cassava is described. MCol 1684 (the best cultivar of the CIAT cassava germ plasm bank) and MPtr 26 were used as the reference cultivars in the experiments, both in the field and in the greenhouse.Rate of leaf photosynthesis was measured by infrared gas analysis. Measurements of the photosynthetic rate were carried out using the youngest fully expanded leaf from plants growing outdoors that were 35 - 45 days old. Maximum photosynthetic rates varied from 0.74 x 10 -6to 0.81 x 10 -6kg CO 2 .m -2leaf.s -1. MCol 22 had the highest leaf photosynthetic rate. A relatively low photonflux density level was required for light saturation of the photosynthetic rate. This is characteristic for a plant species with a C 3 cycle. Photosynthesis increased only slightly from 1000 to 1500 μE .m -2.s -1PAR (photosynthetically active radiation). Light efficiency at low light intensities (α) varied from 9.0 x 10 -9to 12.4 x 10 -9kg CO 2 .J -1. The CO 2 concentration remained at an approximately constant level in the intercellular spaces, independent of the light level, being 212 vppm (0.387 x 10 -3kg.m -2). At a photonflux density of 1500 μE.m -2.s -1mesophyl resistance was higher than leaf resistance to CO 2 (335 s.m -1compared with 185 s.m -1). Transpiration rates did not differ between clones, but increased with light intensity. water use efficiency (WUE)varied from 15.1 to 17.1 mg CO 2 uptake per g H 2 O, and was most efficient for MCol 22.Linear relationships were found between total dry matter yield and the amount of intercepted PAR. Photosynthetic efficiency varied from 1.9% to 2.5%, based on PAR during the first six months of the growth period, and decreased markedly in older plants. The fraction of incoming intercepted PAR varied from 43% to 69% during the first six months. Cultivars had an extinction coefficient (K) of 0.72 to 0.88 and their leaves were dominantly planophile.A leaf area index (LAI) of 1.0 (about 50% light interception) was attained at 60 to 90 days from planting. An LAI = 3, which coincides with a light interception by the leaf canopy of approximately 90% was reached 120 to 150 days after planting, so about 40% of a growth period of one year had elapsed before complete ground cover was achieved. Genotypes with very different canopy characteristics reached an LAI of 3 in approximately the same time.Cassava has an indeterminate habit with sympodial branching. The length of the period until first branching depended on genotype and planting date. Large genetic differences were found in leaf life, leaf size, plant age at which maximum leaf size was reached and leaf formation rate per apex. Small variations in environmental conditions caused significant differences in canopy characteristics.During the growth period of cassava two periods with constant dry matter partitioning could be distinguished, with the apparent initiation of the filling of storage roots (AISS) being the crucial point. A constant proportion of the dry matter formed is distributed to the storage roots: this is the efficiency of storage root production (ESRP). Genetic differences were found for ESRP and AISS.The influence of daylength on growth and yield was studied. Daylength was increased by light bulbs, while the other growth conditions remained similar. Daylength had only a very slight influence on AISS value. ESRP was negatively influenced by long days. Differences in ESRP were the main cause of differences in yield of storage roots for plants grown at different daylengths. For MCol 22, the ESRP value was also considerably lower under long-day conditions, but the yield of storage roots was nevertheless only slightly reduced, because of the higher total dry matter yield. MCol 22 is the first detected cassava clone whose yield of storage roots is nearly dayneutral and thus it is suitable for cultivation at higher latitudes. Long-day conditions caused a large increase in LAI. The higher LAI values were caused by a higher leaf formation rate per apex and a larger number of apices per m 2. Photosynthetic efficiency was not influenced by daylength.The implications of the findings are discussed. Plant properties that could be useful for improving storage root yield are: a high ESRP value, a low AISS value, a high growth vigour (short period until 50% light interception), a light interception of about 90% as long as possible, and a good sink potential.Present knowledge of cassava cultivation techniques is such that high yields are possible. Potential yield of storage roots is about 30 t.ha -1.year -1on dry weight basis and about 90 t.ha -1.year -1on fresh weight basis. The highest recorded yield of fresh storage roots at the CIAT experimental farm is of that order (namely 82 t.ha -1), and was achieved after a growth period of one year

Search for gravitational waves from low mass compact binary coalescence in LIGO's sixth science run and Virgo's science runs 2 and 3

We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009, and October 20, 2010. We searched for signals from binaries with total mass between 2 and 25M⊙; this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass, including the results from previous LIGO and Virgo observations. The cumulative 90% confidence rate upper limits of the binary coalescence of binary neutron star, neutron star-black hole, and binary black hole systems are 1.3×10−4, 3.1×10−5, and 6.4×10−6  Mpc−3 yr−1, respectively. These upper limits are up to a factor 1.4 lower than previously derived limits. We also report on results from a blind injection challenge. © 2012 The American Physical Societ

All-sky search for periodic gravitational waves in the full S5 LIGO data

We report on an all-sky search for periodic gravitational waves in the frequency band 50–800 Hz and with the frequency time derivative in the range of 0 through −6×10−9  Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our Galaxy. After recent improvements in the search program that yielded a 10× increase in computational efficiency, we have searched in two years of data collected during LIGO’s fifth science run and have obtained the most sensitive all-sky upper limits on gravitational-wave strain to date. Near 150 Hz our upper limit on worst-case linearly polarized strain amplitude h0 is 1×10−24, while at the high end of our frequency range we achieve a worst-case upper limit of 3.8×10−24 for all polarizations and sky locations. These results constitute a factor of 2 improvement upon previously published data. A new detection pipeline utilizing a loosely coherent algorithm was able to follow up weaker outliers, increasing the volume of space where signals can be detected by a factor of 10, but has not revealed any gravitational-wave signals. The pipeline has been tested for robustness with respect to deviations from the model of an isolated neutron star, such as caused by a low-mass or long-period binary companion. © 2012 The American Physical Societ

Upper limits on a stochastic gravitational-wave background using LIGO and Virgo interferometers at 600-1000 Hz

A stochastic background of gravitational waves is expected to arise from a superposition of many incoherent sources of gravitational waves, of either cosmological or astrophysical origin. This background is a target for the current generation of ground-based detectors. In this article we present the first joint search for a stochastic background using data from the LIGO and Virgo interferometers. In a frequency band of 600–1000 Hz, we obtained a 95% upper limit on the amplitude of ΩGW(f)=Ω3(f/900  Hz)3, of Ω3<0.32, assuming a value of the Hubble parameter of h100=0.71. These new limits are a factor of seven better than the previous best in this frequency band. © 2012 The American Physical Societ

All-sky search for gravitational-wave bursts in the second joint LIGO-Virgo run

We present results from a search for gravitational-wave bursts in the data collected by the LIGO and Virgo detectors between July 7, 2009 and October 20, 2010: data are analyzed when at least two of the three LIGO-Virgo detectors are in coincident operation, with a total observation time of 207 days. The analysis searches for transients of duration ≲1  s over the frequency band 64–5000 Hz, without other assumptions on the signal waveform, polarization, direction or occurrence time. All identified events are consistent with the expected accidental background. We set frequentist upper limits on the rate of gravitational-wave bursts by combining this search with the previous LIGO-Virgo search on the data collected between November 2005 and October 2007. The upper limit on the rate of strong gravitational-wave bursts at the Earth is 1.3 events per year at 90% confidence. We also present upper limits on source rate density per year and Mpc3 for sample populations of standard-candle sources. As in the previous joint run, typical sensitivities of the search in terms of the root-sum-squared strain amplitude for these waveforms lie in the range ∼5×10−22  Hz−1/2 to ∼1×10−20  Hz−1/2. The combination of the two joint runs entails the most sensitive all-sky search for generic gravitational-wave bursts and synthesizes the results achieved by the initial generation of interferometric detectors. © 2012 The American Physical Societ

Search for gravitational waves from compact binary coalescence in LIGO and Virgo data from S5 and VSR1

We report the results of the first search for gravitational waves from compact binary coalescence using data from the Laser Interferometer Gravitational-Wave Observatory and Virgo detectors. Five months of data were collected during the Laser Interferometer Gravitational-Wave Observatory’s S5 and Virgo’s VSR1 science runs. The search focused on signals from binary mergers with a total mass between 2 and 35M⊙. No gravitational waves are identified. The cumulative 90%-confidence upper limits on the rate of compact binary coalescence are calculated for nonspinning binary neutron stars, black hole-neutron star systems, and binary black holes to be 8.7×10−3  yr−1 L10−1, 2.2×10−3  yr−1 L10−1, and 4.4×10−4  yr−1 L10−1, respectively, where L10 is 1010 times the blue solar luminosity. These upper limits are compared with astrophysical expectations. © 2010 The American Physical Societ

Search for gravitational waves from intermediate mass binary black holes

We present the results of a weakly modeled burst search for gravitational waves from mergers of nonspinning intermediate mass black holes in the total mass range 100–450  M⊙ and with the component mass ratios between 1∶1 and 4∶1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the intermediate mass black holes mergers as a function of the component masses. In the most efficiently detected bin centered on 88+88  M⊙, for nonspinning sources, the rate density upper limit is 0.13 per Mpc3 per Myr at the 90% confidence level. © 2012 The American Physical Societ

Penumbral Rescue by normobaric O = O administration in patients with ischemic stroke and target mismatch proFile (PROOF): Study protocol of a phase IIb trial.

Oxygen is essential for cellular energy metabolism. Neurons are particularly vulnerable to hypoxia. Increasing oxygen supply shortly after stroke onset could preserve the ischemic penumbra until revascularization occurs. PROOF investigates the use of normobaric oxygen (NBO) therapy within 6 h of symptom onset/notice for brain-protective bridging until endovascular revascularization of acute intracranial anterior-circulation occlusion. Randomized (1:1), standard treatment-controlled, open-label, blinded endpoint, multicenter adaptive phase IIb trial. Primary outcome is ischemic core growth (mL) from baseline to 24 h (intention-to-treat analysis). Secondary efficacy outcomes include change in NIHSS from baseline to 24 h, mRS at 90 days, cognitive and emotional function, and quality of life. Safety outcomes include mortality, intracranial hemorrhage, and respiratory failure. Exploratory analyses of imaging and blood biomarkers will be conducted. Using an adaptive design with interim analysis at 80 patients per arm, up to 456 participants (228 per arm) would be needed for 80% power (one-sided alpha 0.05) to detect a mean reduction of ischemic core growth by 6.68 mL, assuming 21.4 mL standard deviation. By enrolling endovascular thrombectomy candidates in an early time window, the trial replicates insights from preclinical studies in which NBO showed beneficial effects, namely early initiation of near 100% inspired oxygen during short temporary ischemia. Primary outcome assessment at 24 h on follow-up imaging reduces variability due to withdrawal of care and early clinical confounders such as delayed extubation and aspiration pneumonia. ClinicalTrials.gov: NCT03500939; EudraCT: 2017-001355-31