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Morphological responses of cocksfoot (Dactylis glomerata L.) and tall fescue (Lolium arundinaceum Schreb.) to waterlogging stress

Nguyen, TM 2022 , 'Morphological responses of cocksfoot (Dactylis glomerata L.) and tall fescue (Lolium arundinaceum Schreb.) to waterlogging stress', Research Master thesis, University of Tasmania.

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Waterlogging is a seasonal constraint on low-lying cropping and pasture lands in temperate regions of south-eastern Australia during winter. It has been attributed to yield loss in both crops and pastures. The tolerance level of plants to waterlogging relates to physiological, biochemical, morphological and anatomical adaptive traits. Understanding the likely response and adaptive characteristics of particular pasture species and cultivar to waterlogging can assist in choosing appropriate cultivars for waterlogging prone areas. In this study, we investigated morphological responses of cocksfoot (Dactylis glomerata L.) and tall fescue (Lolium arundinaceum Schreb., syn. Festuca arundinacea Schreb.) grass plants under waterlogging conditions. The aims of this study were: i) to examine the morphological responses of two temperate perennial grass species: tall fescue and cocksfoot under waterlogging conditions; ii) to determine which mechanisms are involved in plant adaptation to waterlogged conditions.
Two separate pot experiments were conducted at Tasmanian Institute of Agriculture, Mt. Pleasant Laboratory, Launceston, Tasmania, Australia. The first experiment was conducted from April until October 2019 on four cultivars of tall fescue (two winter active cultivars of Mediterranean origin: cv. Resolute and cv. Temora and two summer active cultivars of Continental origin, cv. Hummer and cv. Quantum II MaxP); and four cultivars of cocksfoot (two winter active cultivars of Mediterranean, cv. Kasbah and cv. Uplands and two summer active cultivars of Continental, cv. Lazuly and cv. Porto). The 14-week-old plants were subjected to waterlogging or control conditions for 4 weeks, followed by a 4-week recovery period.
The second experiment was conducted from May to August 2020 on two summer active cultivars of Continental origin of tall fescue, cv. Hummer and cv. Quantum II MaxP; and two summer active cultivars of Continental origin of cocksfoot, cv. Lazuly and cv. Porto. The 6-week-old plants were subjected to four periods of waterlogging treatments: 7, 14, 21 and 28 days. Measured above ground parameters included plant height, number of live tillers, leaf chlorophyll content (measured by Soil Plant Analysis Development (SPAD) reading) and shoot dry matter; and below ground included root length, number of adventitious roots, the formation of aerenchyma in adventitious roots and root dry matter.
Results showed that waterlogging did not affect shoot dry matter of both grass species in both experiments but did significantly affect the development of root system. Cocksfoot appeared to be more sensitive to waterlogging than tall fescue, which was indicated in most of the variables measured such as plant height, leaf chlorophyll content (measured by SPAD reading), root length and root dry matter. Waterlogging significantly induced the formation of adventitious roots and aerenchyma in the roots of all cultivars. However, aerenchyma formed significantly faster and to a greater extent in waterlogged tall fescue plants (cv. Hummer and cv. Quantum II MaxP), compared to waterlogged cocksfoot plants (cv. Lazuly and cv. Porto). The formation of aerenchyma in adventitious roots is a possible mechanism that aided tall fescue plants overcome waterlogging stress on root length development, whereas root length of all cocksfoot cultivars (cv. Lazuly, cv. Porto, cv. Uplands and cv. Kasbah) was significantly impeded by waterlogging. Hence, the proportion of aerenchyma formed in adventitious roots appeared to be the major contributor to root survival and growth under waterlogging conditions. However, waterlogging significantly caused the reduction in root dry matter of all cultivars of tall fescue and cocksfoot examined in the second experiment, most likely attributed to younger age of plants when waterlogging was started. Further investigations on aerenchyma formation in primary roots would be interesting to assess whether the loss of primary roots under waterlogging is related to capacity for aerenchyma formation in these roots of cocksfoot and tall fescue plants.
Results of this study did not show any significant differences between the two origin types (Mediterranean and Continental types) of each species in their response to waterlogging. Therefore, it is likely that differences in response of these grasses to waterlogging depend on adaptive characteristics of individual cultivar rather than origin of the breeding material per se. Results of the first experiment showed that the Mediterranean cocksfoot cv. Kasbah, was the most sensitive cultivar to 4 weeks waterlogging in all measured variables, whereas cv. Uplands, also a Mediterranean cocksfoot cultivar, showed better tolerance to waterlogging. A variation in waterlogging responses among cultivars suggests the need for further investigation to elucidate differences in physiological and morphological mechanisms of waterlogging tolerance (e.g. aerenchyma and adventitious roots) among cultivars and pre-breeding material within species, which could then be used in grass breeding programs.

Item Type: Thesis - Research Master
Authors/Creators:Nguyen, TM
Keywords: Cocksfoot, tall fescue, waterlogging, aerenchyma, adventitious roots
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