Effects of Kinetin, Coconut Milk and Calcium Chloride on Biochemical Indices of Boro Rice (Oryza Sativa L.) in Presence of Higher Manganese Condition of Acid Soil
Abstract
In North-east India including Assam, available Manganese [Mn2+] in soil is 3-52 ppm with a critical limit 2-3 ppm. In plants, [Mn2+] is 15-20 ppm g-1 dry weight, in excess of which Mn becomes toxic to crop plants (Basumatary et al., 2014). There is a paucity of information on the effects of natural or synthetic plant growth regulating subnstances viz., Cytokinin, Coconut milk and Calcium chloride on amelioration of Mn toxicity of rice crop grown in acid soil condition of Assam. So, a pot experiment was conducted to investigate into the effects of root-dip treatments of rice crop with these substances on biochemical performance of four rice genotypes (Kanaklata, Bishnuprasad, Jyotiprasad and Numoli) cultivated in acid soil enriched with higher Mn (30ppm native Mn plus 20ppm added Mn). At 20 ppm Mn application, there were decreases in total chlorophyll content (14.52%), NRactivity (17.77%), Carbohydrate content (3.83%). In contrast, soil treated with 20 ppm Mn as basal at vegetative stage along with the overnight (≈12h) root dip treatments (RDT) of rice varieties with Cytokinin (100ppm), Coconut milk (10 times dilution) and CaCl (100ppm), enhenced Cholorophyll a (3-525-19.771%), 2 Chlorophyllb (1.917-19.55%), total chlorophyll contents (4.13-6.35%),) in leaf, NRactivity (4.46-10.08%) and carbohydrate content ingrain (2.24-10.92%). The variety, Kanaklata was found to be the best based on the biochemical parameters (total Chl:1.861 mg g-1 f.w, Chl ‘a’ (0.924 mg g-1 f.w), Chl ‘b’ (0.933 mg g-1 f.w), Carbohydrate: 9.202 mg g-1, and [Ca2+] in roots (59.35ppm).
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Introduction
Manganese (Mn) being a micronutrient, at a congenial concentration plays vital roles on growth and development of rice crop cultivated on acidic soil condition. Mn is involved inactivating more than 35 enzymes in plants (Mousavi et al., 2011), Mn2+ along with Ca2+ has the power of catalysing the Hill'sreaction in the process of photosynthesis (Aref, 2012). Application of Mn especially on older leaves helps in photoassimilation (Agustina, 2011). Because, Mn influences chlorophyll synthesis, and its presence is essential in photosystem II (Diedrick, 2010). However, an excess of Mn2+ is toxic for most plants (Millaleo et al., 2010). Moreover, Mn2+ becomes toxic to all susceptible plants on acid soils in contrast to calcareous soils (high soil pH) and organic soils (Alejandro et al., 2020).
Information how the excess Mn2+ brings about biochemical changes in upland rice crop grown in acid soil condition of Assam are available (Yomso and Bharali, 2021). Efforts on amelioration of physio-biochemical disorders in Boro rice due to higher Mn2+ are lacking. It'sknown that Cytokinin is involved in cell division, and Calcium is one of the integral components of cell wall and cell membrane in plants (Bharali et al., 2015). The hypothesis was that accumulation of root biomass through its proliferation, and maintenance of membrane integrity either directly by adherence of [Ca2+] or indirectly by the action of growth regulating substances impart tolerance to Mn2+ toxicity on rice crop in acid soil condition of Assam. Therefore, the present research work was carried out incorporating Cytokinin, Coconut milk and Calcium chloride as root dip treatments of upland (Boro) rice crop in presence of higher Mn in acid soil condition.
