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Genotypic Variations in Root Traits of Wheat Varieties at Phytomer Level

Dr. A. B. M. Arif Hassan Khan Robin
Associate Professor
Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Mymensingh-2202Bangladesh

Abstract/ Executive Summary:

The aims of this study were to investigate genotypic variations in root traits at phytomer level of wheat varieties and for recommending a few root traits as selection parameters in future breeding programs. Two separate experiments were conducted to measure their root traits for hydroponically grown wheat plants. In Experiment 1, main axis length, root hair density and diameter differed from phytomer to phytomer at 60 days after sowing for two varieties, Shotabdi and Sonalika. Density of first order laterals at their axis of origin, dry weights of roots and shoots and root:shoot ratio varied significantly among 8 varieties. In Experiment 2, number of root bearing phytomer, total number of adventitious roots, main axis length at root bearing phytomer 1 and 2 (youngest roots were the reference point and numbered as phytomer 1), length of first order laterals at phytomer 3, root hair density and dry weights of roots and shoots were significantly different among varieties. PC1 (principal component 1) resulted in significant variation among varieties for number of live leaves, new roots appeared, number of root bearing phytomer, total number of adventitious roots, root dry weight and shoot dry weight. PC2 yielded significant difference among varieties for live leaves, main axes length at phytomer 1 & 2, number of new roots, root hair density and diameter. Selection of varieties based on main axes length at the youngest phytomer & root hair density per unit surface area along with dry weights of roots and shoots could be recommended for future breeding program as these four parameters consistently resulted in significant variation among varieties.

Keywords: Wheat, Phytomer, Root hairs, Lateral roots

Location: Mymensingh

Start Date: 00-11-2012

End Date: 00-02-2013

Program Area: Variety and Species

Commodity: Wheat

Objectives:

To investigate root growth and development of 13 wheat varieties at the phytomer level to select out the variable root traits, including the traits related to root hairs.

Methodology:

The experiment was conducted at the Department of Genetics and Plant Breeding, Bangladesh Agricultural University. Seeds of thirteen elite wheat varieties were collected from the Wheat Research Centre of the Bangladesh Institute of Agricultural Research, Gazipur. Two separate experiments were conducted during rabi season (November to February) of 2012 – 2013 in Bangladesh. Experiment 1 was conducted with 8 selected varieties out of 13. Seeds of the selected varieties were placed for germination on 26 November 2012. Experiment 2 was started one month later from 26 December 2012. Seeds were germinated in clean tap water floated in foam net inside the plastic trays in both experiments. Around 200 seeds were germinated per tray for each variety in order to select 15 healthy seedlings with synchronized leaf appearance at transplanting in hydroponic nutrient solution. Seed germination process took 3 to 4 days. Seedlings were transplanted in hydroponic solution following a completely randomized design with 15 and 10 replicates for each of the thirteen varieties in Experiment 1 and Experiment 2, respectively. There were 10 individual trays; each tray contained 13 individual plants, for setting up the whole experiment in both Experiment 1 (8 varieties x 15 replicates) and Experiment 2 (13 varieties x 10 replicates). Each tray contained 13 plants, one from each variety. Thus a total of 120 and 130 individual plants were maintained in Experiment 1 and Experiment 2, respectively.Plants in each tray rotated their position randomly every week to avoid any position effect. Leaf appearance interval of all varieties was monitored for two weeks and that was calculated around 10 days (90^oC days). Plants were fed with following nutrient solution: 1mM NH₄NO₃, 0.6mM NaH₂PO₄.H₂O, 0.6mM MgCl₂.H₂O, 0.3mM K₂SO₄, 0.3mM CaCl₂.H₂O, 50μM H₃BO₃, 90μM Fe-EDTA, 9μM MnSO₄.4H₂O, 0.7μM ZnSO₄.7H₂O, 0.3μM CuSO₄.5H₂O, 0.1μM NaMoO₄.2H₂O dissolved in tap water. The nutrient solution was refreshed weekly. All plants were under similar management until the destructive harvest

Source of Information: J. Bangladesh Agril. Univ. 12(1): 45–54, 2014, ISSN 1810-3030

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

A shorter main axis length at Pr6 compared to Pr5 suggested that the root position perhaps achieved maximum possible axis length at Pr6. The youngest root bearing phytomer receives most part of photo-assimilate and that decreases gradually towards the older phytomer. Substrate supply usually diminishes below Pr6 in perennial ryegrass. Pr6 was developed at the very early stage, around 50 days before the day of destructive harvest when plant size was small. Root hair density was directly correlated with surface area of axis of origin (r= 0.365, p= 0.014) suggesting that the more the epidermal cells available the higher the chance of root hair formation. Main axis length at Pr1 and Pr2 brought significant difference among 13 wheat varieties but at Pr3 and Pr4 that difference was not significant. It is important to note couple of issues in comparing main axis length among varieties: i) main axis elongated at the Pr1 and Pr2 at a faster rate compared to the older root bearing phytomers, ii) main axisfor a particular Pr at different replicates of same variety and different varieties did not appear at the same day, iii) destructive harvest process took 3-5 days across two experiments. Therefore in any further experimentation main axis elongation rate might be accounted in thermal time in rhizochron (root appearance interval) time scale for more validity. Significant difference in main axis elongation rate suggests that estimating main axis elongation would be regarded as an important selection criterion. PC2 indicated that main axis length at Pr1 and Pr2 is positively associated with number of live leaves present in main tiller. Root growth and root elongation rate were also significantly different in some previous studies. First order lateral generally initiate at the Pr2 or Pr3. Significant variation in length of first order laterals at Pr3 suggested that at Pr3 the laterals were at active elongation process, the same happens for main axis at Pr1 and Pr2. PC1 showed that new root formation, number of root bearing phytomers, total number of adventitious roots per plant, and dry weights of roots and shoot are closely associated and hence directly dependent to number of live leaves per plant. Dry weights of roots and shoots were consistently different among varieties across the experiments. The results suggested these two traits should be always regarded as selection parameters. Root hair density was marginally different among 13 wheat varieties in Experiment 2 suggesting that this trait is important to consider as previous reports also indicated that under various stress condition root hair density was variable. Based on the results of the two experiments the following root traits can be recommended for future breeding program: i) main axis length at the youngest 2-3 root bearing phytomer, ii) density and diameter of the root hairs along with root dry weight and shoot dry weight of the main tillers as all those traits were consistently significant across two experiments.

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