Matthew D Robbins | PubMed Health

PubMed2006

Population development by phenotypic selection with subsequent marker-assisted selection for line extraction in cucumber (Cucumis sativus L.).

Cucumber (Cucumis sativus L.; 2n = 2x = 14) has a narrow genetic base, and commercial yield of US processing cucumber has plateaued in the last 15 years. Yield may be increased by altering plant architecture to produce unique early flowering (days to flower, DTF), female (gynoecious, GYN), highly branched (multiple lateral branching, MLB), long-fruited (length:diameter ratio, L:D) cultivars with diverse plant statures. The genetic map position of QTL conditioning these quantitatively inherited yield component traits is known, and linked molecular markers may have utility in marker-assisted selection (MAS) programs to increase selection efficiency, and effectiveness. Therefore, a base population (C0), created by intermating four unique but complementary lines, was subjected to three cycles (C1-C3) of phenotypic (PHE) mass selection for DTF, GYN, MLB, and L:D. In tandem, two cycles of marker-assisted backcrossing for these traits began with selected C2 progeny (C2S) to produce families (F1[i.e., C2S x C2S], and BC(1) [i.e., F1 x C2S]) for line extraction, and for comparative analysis of gain from selection by PHE selection, and MAS. Frequencies of marker loci were used to monitor selection-dependent changes during PHE selection, and MAS. Similar gain from selection was detected as a result of PHE selection, and MAS for MLB (approximately 0.3 branches/cycle), and L:D (approximately 0.1 unit increase/cycle) with concomitant changes in frequency at linked marker loci. Although genetic gain was not realized for GYN during PHE selection, the percentage of female flowers of plants subjected to MAS was increased (5.6-9.8% per cycle) depending upon the BC1 population examined. Selection-dependent changes in frequency were also detected at marker loci linked to female sex expression during MAS. MAS operated to fix favorable alleles that were not exploited by PHE selection in this population, indicating that MAS could be applied for altering plant architecture in cucumber to improve its yield potential.

Biomarkers↗

PubMed2005

Duty cycle and modulation efficiency of two-channel Hadamard transform time-of-flight mass spectrometry.

Hadamard transform time-of-flight mass spectrometry (HT-TOFMS) is based on the pseudorandom gating of ion packets into a time-of-flight mass-to-charge analyzer. In its typical implementation, the technique is able to monitor continuous ion sources with a 50% duty cycle, independent of all other figures of merit. Recently, we have demonstrated that the duty cycle can be extended to 100% using patterned, two-channel detection. Two-channel HT-TOFMS involves the simultaneous optimization of paired one-channel experiments and imposes more stringent conditions to achieve high-quality spectra. An ion modulation device, known as Bradbury-Nielson Gate (BNG), is central to HT-TOFMS. It is an ideal deflection plate, capable of transmitting or deflecting an ion beam according to a known binary sequence without changing the times-of-flight of the ions. Analytical equations are derived that accurately describe the ion modulation process of the BNG as confirmed by good agreement with SimIon simulations and ion beam imaging experiments. From these expressions, the duty cycle and ion modulation efficiency were calculated for various BNG parameters, ion beam characteristics, and detector dimensions, which permit the optimum conditions to be chosen for the two-channel experiment. We conclude that the outer detector should be three times the maximum deflection angle to detect all deflected ions (100% duty cycle) and that the difference between the modulated ion counts in the sequence elements 0 and 1 should be maximized to achieve high modulation efficiency. This condition is best achieved by tight focusing of the ion beam in the center of the inner detector. When both channels are optimized, the two-channel advantage can be exploited to achieve a further improvement over a single-channel experiment.

Algorithms↗