1 Cooperative Research Centre for Plant-Based Management of Dryland Salinity, The University of Western Australia, University Field Station, 1 Underwood Avenue, Shenton Park, WA 6009, Australia. Emails: firstname.lastname@example.org and email@example.com
2 School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. Email: firstname.lastname@example.org
3 New South Wales Department of Primary Industries, Wagga Wagga Agricultural Institute, Private Mail Bag, Wagga Wagga, NSW 2650, Australia. Email: email@example.com
Medicago sativa L. (lucerne) is the main perennial forage legume used in cropping and grazing systems of southern Australia. Lucerne lacks adaptation to waterlogging and this has highlighted a need for perennial forage legumes adapted to winter waterlogged areas that experience significant summer drought. The Lotus genus contains many perennial species and some of these are reported to be waterlogging tolerant. We studied this genus to identify those species most tolerant of waterlogging in potting mix, as well as the extent of intra species variation that could be exploited in plant breeding. Twelve Lotus species and lucerne were compared for waterlogging tolerance in a 3 replicate pot experiment containing 5 plants per pot. After 8 weeks of growth, treatments were applied and included a drained control, a waterlogged (6 weeks) plus free draining combination (5 weeks) and a continuously waterlogged treatment (11 weeks). Measurements were taken at weeks 8, 14 and 19 and included, root and shoot dry weights, presence of adventitious roots, ‘split stem bases’, surface roots and ability to form aerenchyma. The most waterlogging-tolerant Lotus species were L. corniculatus L., L. glaber Mill. and L. pedunculatus Cav.. Each of these species developed aerenchyma, adventitious roots, surface roots and ‘split stem bases’ to improve oxygen transport to the root tips. Significant intra species differentiation between populations of the same species was found, highlighting the opportunity for genetic improvement. The remaining species were less tolerant to waterlogging, with lucerne, L. azoricus P.W. Ball and L. latifolius Brand. the most susceptible. For application to the field, these species now need to be screened in or using waterlogged soil from the target environments.
Lotus, Lucerne, waterlogging.
The harsh dry summers in southern Australia can last for 3 to 8 months with very little or no rainfall and high evaporative demands. Lucerne survives these conditions by first, escaping the drought by being able to utilize water stored at depth in the soils with its deep root system and secondly when there is shortage of water by shedding its leaves and reducing its evaporation rates allowing it to remain alive during summer whilst utilizing stored carbohydrates. These strategies ensure lucerne survives significant summer droughts. However, parts of these landscapes are also waterlogged in winter and in these circumstances seedlings of lucerne are often decimated while established stands experience significant plant death. Hence no adequate perennial legume option exists for circumstances where winter waterlogging is followed by summer drought.
Lotus corniculatus L. and Lotus glaber Mill. from North Africa, Europe and Asia and Lotus pedunculatus Cav. (syn. L. uliginosus Schkuhr) from the Mediterranean basin and northern Europe are the main species used as pasture legumes from the Lotus genus and all of them are well known for their waterlogging tolerance (Blumenthal and McGraw 1999; Striker et al. 2005). Therefore, these 3 species together with Lotus australis Andrew and Lotus cruentus Court from Australia; Lotus creticus L. from the Mediterranean basin; and Lotus argyrodes R.P. Murray, Lotus azoricus P.W. Ball, Lotus campylocladus Webb & Berthel, Lotus glaucus Sol., Lotus latifolius Brand, Lotus macranthus Lowe from Macronesia Islands were evaluated for waterlogging tolerance and compared with lucerne.
Twenty-one accessions corresponding to the 12 Lotus species and lucerne cv. Sceptre were established under well drained conditions in 4.4 L pots filled with commercial potting mix. In each pot, eight 3-days old pre-germinated seedlings were transplanted and subsequently thinned to 5 plants per pot. All treatments were replicated 3 times. Eight weeks after sowing, the first harvest was taken and the treatments were imposed. One third of the pots remained drained and two thirds were waterlogged. The waterlogged treatment was imposed by putting the pot inside a bucket of the same size so that there was no drainage and the water was kept at the surface of the pot for the waterlogged period. After 6 weeks of being waterlogged, half of them were taken out of the buckets allowing them to recover from the waterlogging period and the remaining half was kept under waterlogging conditions until the end of the experimental period for 5 weeks more. Plants were harvested when treatments were imposed and at the end of the experiment to determine the plant responses to waterlogging in comparison with the drained or recovered treatments. In each harvest the following measurements were taken: root and shoot dry weights, nodule rating, presence of adventitious roots, ‘split stems’, presence of surface roots and ability to form aerenchyma.
The most waterlogging tolerant species, as determined by the final harvest, was L. glaber which had a 3% increase in shoot weight, a 12% increase in root weight and a 50% reduction in root length relative to drained plants. The next most tolerant species included L. corniculatus and L. pedunculatus. Lucerne, as expected, was highly susceptible to waterlogging (Cocks 2001; Humphries and Auricht 2001) with final shoot dry weight reduced by 89%, root dry weight reduced by 97% and root length reduced by 51%. Other highly susceptible species included L. azoricus and L. latifolius. All other species were considered moderately susceptible to waterlogging. The mechanisms observed to facilitate oxygen transfer to roots were the presence of aerenchyma, adventitious roots, surface roots and/or ‘split stems’. Surface roots and adventitious roots were only produced by the 3 most tolerant Lotus species, while these attributes were not exhibited by lucerne or L. argyrodes. Within the most tolerant lotus species, variability in response to waterlogging within and between accessions was recorded (data not shown) indicating further genetic gain may be possible via plant breeding.
Under well drained conditions Lotus corniculatus, Lotus glaber, Lotus pedunculatus and lucerne were the most productive species, while lucerne also allocated the most biomass to roots. Most species had a well developed root system with the exception of L. creticus and L. macranthus. Nodulation success was recorded in all species and accessions.
Lotus glaber, L. corniculatus, and L. pedunculatus were the most tolerant of waterlogging, confirming their potential as forage legumes for winter waterlogged areas. Furthermore, lucerne was confirmed to be highly susceptible to waterlogging. None of the other 9 Lotus species were adapted to waterlogged conditions making them unsuitable for winter waterlogged areas. The most waterlogging tolerant species also exhibited within species variation that could be further utilised via plant breeding efforts. These results now need to be validated in or using soils from the target environments. Further research is also required to establish if waterlogging tolerance at the growth stages evaluated here are also relevant to when waterlogging occurs at other times or durations.
Blumenthal MJ, McGraw RL (1999) Lotus adaptation, use and management. In 'Trefoil: the science and technology of Lotus'. (Ed. PR Beuselinck) pp. 97-119. (American society of agronomy, Inc. & Crop science society of America, Inc.: Madison, Wisconsin).
Cocks PS (2001) Ecology of herbaceous perennial legumes: a review of characteristics that may provide management options for the control of salinity and waterlogging in dryland cropping systems. (Special issue: Towards a farming future: water control by perennials in cropland). Australian Journal of Agricultural Research 52, 137-151.
Humphries AW, Auricht GC (2001) Breeding lucerne for Australia's southern dryland cropping environments. (Special issue: Towards a farming future: water control by perennials in cropland). Australian Journal of Agricultural Research 52, 153-169.
Striker GG, Insausti P, Grimoldi AA, Ploschuk EL, Vasellati V (2005) Physiological and anatomical basis of differential tolerance to soil flooding of Lotus corniculatus L. and Lotus glaber Mill. Plant and Soil 276, 301-311.