Root and shoot phenotyping to identify heat-resistant lettuce within recombinant inbred line populations

Project Number
RI 9/10 HJ

Project Duration
January 2011 - March 2016

Status
Completed

Abstract
Our previous research has successfully grown temperate and subtropical vegetable crops (eg. lettuce, capsicum, Chinese broccoli, tomato, and Chinese cabbage) in tropical Singapore by cooling (12-25 degree Celsius) only their root zone while shoots were exposed to hot fluctuating ambient temperatures (24-38 degree Celsius), which has lead to the development of a new industry. However, energy costs incurred by root zone cooling mean that identifying heat-resistant crop varieties may be a highly effective means to minimize the cost of production. Inhibition of lettuce (Lactuca sativa) growth in warm regions is mainly due to poor root development such as corky root, plant dieback and tip burn. In this project, recombinant inbred lines (RILs) of a lettuce population obtained from crosses between thermosensitive (Lactuca sativa L. 'Salinas') and thermotolerant (L. serriola accession UC96US23) genotypes (made by researchers at UC Davis, USA) will be phenotyped to identify heat-tolerant lettuce. Of these lines, some may already be suitable for commercial production, or genomic regions from these lines (that confer heat tolerance) may be incorporated into existing elite cultivars to develop new heat-resistant varieties. Plant root systems exhibit a high degree of architectural plasticity in response to environmental stresses such as rootzone temperature (RZT), water and nutrient availability. To improve crop growth in stressed environments, root phenotyping must be targeted towards the likely stresses faced by plants. Phenotyping large numbers of lines is problematic because of the difficulties of growing and analyzing sufficient plants, and the many such efforts have grown young seedlings in artificial homogeneous media. However, the aeropinics (root systems suspended in air and sprayed with nutrient solution) system to be used in this project is a powerful tool to non-destructively study root architecture in a commercially relevant production system. The recombinant inbred lines (RILs) will be aeroponically grown to measure shoot and root productivity under hot ambient temperatures (28-38 degree Celsius) to identify variation in RZT tolerance. Mechanistic aspects including shoot/root biomass allocation, root development and nutrient/water uptake, and shoot transpiration and photosynthesis will be measured. These data will allow genetic analysis to identify genomic regions (quantitative trait loci - QTL) controlling these variables, and to determine whether root and whoot phenotypes are closely genetically linked. These data will be combined with previous phenotyping and QTL analysis conducted by researchers at UC Davis, to determine whether root growth under aeroponic conditions is a suitable physiological screen for root traits that may be important in mediating plant response to other stresses (eg. water and nutrient deficits). This will potentially allow world-wide exploitation of the results obtained in this project, to improve resistance of lettuce crops to various stresses.

Funding Source
NIE

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