QTL associated with heat susceptibility index in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) under short-term reproductive stage heat stress

Heat stress adversely affects wheat production in many regions of the world and is particularly detrimental during reproductive development and grain-filling. The objective of this study was to identify quantitative trait loci (QTL) associated with heat susceptibility index (HSI) of yield components in response to a short-term heat shock during early grain-filling in wheat. The HSI was used as an indicator of yield stability and a proxy for heat tolerance. A recombinant inbred line (RIL) population derived from the heat tolerant cultivar ‘Halberd’ and heat sensitive cultivar ‘Cutter’ was evaluated for heat tolerance over 2 years in a controlled environment. The RILs and parental lines were grown in the greenhouse and at 10 days after pollination (DAP) half the plants for each RIL received a three-day heat stress treatment at 38°C/18°C day/night, while half were kept at control conditions of 20°C/18°C day/night. At maturity, the main spike was harvested and used to determine yield components. A significant treatment effect was observed for most yield components and a HSI was calculated for individual components and used for QTL mapping. QTL analysis identified 15 and 12 QTL associated with HSI in 2005 and 2006, respectively. Five QTL regions were detected in both years, including QTL on chromosomes 1A, 2A, 2B, and 3B. These same regions were commonly associated with QTL for flag leaf length, width, and visual wax content, but not with days to flowering. Pleiotropic trade-offs between the maintenance of kernel number versus increasing single kernel weight under heat stress were present at some QTL regions. The results of this study validate the use of the main spike for detection of QTL for heat tolerance and identify genomic regions associated with improved heat tolerance that can be targeted for future studies.     

Natural and synthetic podolactones with potential use as natural herbicide models

A collection of 11 natural and synthetic podolactones have been tested as allelochemicals in a range between 10(-4) and 10(-9) M, and their potential use as natural herbicide models is discussed. Their effects on the germination and growth of the dicots Lactuca sativa (cv. Nigra and cv. Roman), Lepidium sativum, and Lycopersicon esculentum and the monocots Allium cepa, Hordeum vulgare, and Triticum aestivum as standard target species have been studied. An important inhibitory effect on the germination and growth of all tested species (average = 90%) was produced by compounds 9-11 at 10(-4) M. The specific structural requirements related to their activities are studied. On the basis of these results, their use as potential natural herbicide models is proposed.     

Bosonic stimulation in the formation of a bose-einstein condensate

The formation of a Bose-Einstein condensate of a dilute atomic gas has been studied in situ with a nondestructive, time-resolved imaging technique. Sodium atoms were evaporatively cooled close to the onset of Bose-Einstein condensation and then suddenly quenched to below the transition temperature. The subsequent equilibration and condensate formation showed a slow onset distinctly different from simple relaxation. This behavior provided evidence for the process of bosonic stimulation, or coherent matter-wave amplification, crucial to the concept of an atom laser.