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Centre for Plant & Water Science 2008 Annual Report SCREENING OF TOMATO GERMPLASM FOR DROUGHT TOLERANCE SUMMARY Drought is an important abiotic stresses for crop production. With climate change, episodes of droughts are predicted to be frequent affecting crop yield and quality. Furthermore, pricing for water and decreasing allocation entrust pressures on irrigators. With this in mind a project is underway to screen for drought tolerance amongst tomato genotypes. The extent and duration of both intermittent and terminal drought stress impact on yield and quality and their effects can be amplified by interactions with high temperature, disease and hostile soil conditions. Detailed physiological characterisation becomes an important step for effective germplasm screening for utilizing such traits in breeding. In this project we aimed to develop methods for tomato drought screening, and link physiological traits with drought tolerance. Eighteen tomato lines from the world vegetable centre (AVRDC) Taiwan were tested under semi-controlled environments of the glasshouse or screen house at CPWS CQUniversity, Rockhampton in three trials (1. Drought pool, 2. Terminal drought, and 3. Deficit irrigation) during the 2007-2008 season. (a) (b) (c) Tomato accessions tested in: (a) drought pool experiment, (b) terminal drought, and (c) deficit irrigation experiments. Figure 1. Changes in soil water content at different depth in the tomato drought pool and tolerant accessions were capable of drawing soil water at deeper depths and lower than 15% water content. Experimental approach 1 – Drought pool S. pimpinellifollium accessions L3708 and LA1579 showed drought tolerance under declining soil moisture regimes as measured by number of flower bunch, fruits and biomass yield. These accessions also consistently showed lower crop water stress index and electrolyte leakage, lower leaf water potential and greater osmolality, plant height and delayed wilting compared to standard check Arka Meghali and hybrid check Trifecta. Experimental approach 2 – Terminal drought In the terminal drought experiment each accession was planted (15 August 2008) in an individual cylindrical container (130 L, 60 cm diameter x 85 cm height), in two replications, in a randomised fashion containing 169 kg of soil at field capacity (Figure 3). Relative ranking of the accessions for days to permanent wilting, monitoring of growth, development and physiological response was 43
Centre for Plant & Water Science 2008 Annual Report carried out as in the Drought pool experiment. Root length density distribution and root phenotyping was also conducted for each accession. Tomato accessions tested in terminal drought experiment, and approach for root recovering for phenotyping and RLD mapping. The results of the terminal drought experiment suggested that the wild tomato accessions L3708 and LA1579 (S. pimpinellifollium) and LA1940 (S. pennellii) had highest root length density and greatest root penetration compared to all other tested accessions (Figure 4). Delayed symptoms of permanent wilting noted in this experiment as well as in the drought pool experiment may well be associated with greater root foraging for soil water in these wild tomato accession under declining soil moisture regimes. Experimental approach 3 – Deficit irrigation In the deficit irrigation experiment each accession was planted (18 July 2008) in individual bucket containers (20 L, 25 cm diameter x 45 cm height) containing 27 kg of soil maintained at two different soil moisture levels [(field capacity and deficit irrigation (50% of FC)], replicated twice in a randomised fashion with daily irrigation supplied to maintain each treatment (Figure 5). Daily evapotranspiration requirements of each accession, crop water use, water use efficiency, stomatal frequency, distribution and sizing were studied in this trial, and measurements for soil moisture, physiological, morphological, growth and development traits and yields were assessed at monthly intervals. Under deficit irrigation the wild tomato accessions L3708 and LA1579 (S. pimpinellifollium) and LA1940 (S. pennellii) transpired least amount (20-45% of Arka Meghali) compared to all other accessions. However, the dry biomass production by these accessions under deficit irrigation was comparable to those highest transpiring accession such as Arka Meghali. Drought tolerant wild accessions showed sustained growth, slow development of drought symptoms, and were capable of producing flowers, fruits and completion of full life cycle under declining soil moisture conditions similar to terminal drought in field environments. It appears that root traits and leaf osmotic adjustment play key role on conferring drought tolerance in these accessions. However, their fruit quality was extremely poor and these plants have viny growth habit with profuse flowering and fruiting. However, they show promise for utilization of their candidate drought tolerant genes for crossing with appropriate cultivated tomato. Further research is required for detailed phenotying of drought tolerant traits and confirm these preliminary findings. Project Staff Dr Surya P Bhattarai Prof David Midmore Dr Robert de la Pena Dr Sanjay Singh Laurie Tait Delphine Lacombe Funding AVRDC, the World Vegetable Centre, Taiwan & CQUniversity Income $29,985.00 AUD and $33,000.00 USD 44
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Centre for Plant & Water Science - Central Queensland University

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