Final Report Summary - ELITE (Mapping quantitative trait loci for water use efficiency in potato (Solanum tuberosum).)
Potato (Solanum tuberosum) is very sensitive to water-stress when compared to other species. Climate models predict that drought episodes will become more frequent due to the long–term effects of global warming thus putting potato sustainable production at immense risk. Our project aims at improving knowledge base for drought tolerance and water use efficiency (WUE) in potato. Specifically our targets include i) developing a knowledge base on physiological mechanisms of potato crop adaptation to water stress, 2) identification of Quantitative Trait Loci (QTL) for WUE and 3) validation of candidate genes. In addressing our research target we exploited the existing genetic variation in a diploid mapping population (06H1). Results showed that substantial variation exists in canopy temperature between genotypes while demonstrating a link between high stomatal conductance and yield with the help of infra- red thermography (IRT) under well watered field grown conditions. QTL for stomatal conductance was found on the linkage group 2 while QTL for stomatal conductance and interaction with yield is identified on linkage group VII. By comparing the positions of gene-based markers linked to QTLs on the potato genome sequence, we identified candidate genes underlying these QTLs. With a view of understanding gene expression profile under water stress we adopted a controlled experiment under varying degrees of water stress using the cultivar Desiree. Validation of the results from QTL with POCI (Potato Oligo Chip Initiative) array and qPCR showed that ABA related gene showed differential expression under water stress. In order to evaluate the effect of stress on different physiological and morphological parameters, genotypes from 06H1 population representing extremes in respect to transpiration/canopy temperature were selected and grown in a controlled glasshouse under well- watered (WW) and water stressed (WS) conditions in a randomised complete block design (RCBD) with three replications. Morphological traits such as fresh shoot weight, dry shoot weight, fresh root weight, dry root weight, number of tubers, and tuber yield and physiological parameters including leaf chlorophyll content (SPAD index), chlorophyll fluorescence (Fv/ Fm), canopy temperature, relative water content, photosynthetic rate and stomatal conductance were evaluated. Result shows that potato exhibits genotypic differences in agronomic, morphological and physiological traits under WW and WS conditions. Drought stress increased leaf chlorophyll (SPAD index) and chlorophyll fluorescence (Fv/ Fm) in potato. Potential yield of an individual cultivar as well as inherent drought tolerance mechanism is critical for its sustainable production under WS. Cultivars that show robust rooting system have the potential of increasing tuber yield and should be considered for genetic improvement under drought. In addition, for a rooting system to be positively associated with tuber yield, it should not be compensatory to root dry biomass. High photosynthetic rate reduced shoot biomass production without affecting tuber yield. The result of Principal Component Analysis (PCA) shows that genotypes behave differently under optimal and water stress conditions. An ability to understand these differences offers hope for sustainable breeding for drought tolerance in potato. Correlation analyses of tolerance and susceptibility indices shows that drought resistance index, drought susceptibility index and harmonized mean productivity are good screening indicators for selection. This dataset allowed us to make a selection of cultivars under water stress treatment and further screening will be done to judge the potential of these genotypes for sustainable production under stress conditions.