Abstract
Malformation of mango inflorescences (MMI) disease causes severe economic losses worldwide. Present research investigates the underlying causes of MMI. Results revealed significantly higher levels of cyanide, a by-product of ethylene biosynthesis, in malformed inflorescences (MI) of mango cultivars. There was a significant rise in ACS transcripts, ACS enzyme activity and cyanide and ethylene levels in MI as compared to healthy inflorescences (HI). Significant differences in levels of methionine, phosphate, S-adenosyl-L-methionine, S-adenosyl-L-homocysteine, ascorbate and glutathione, and activities of dehydroascorbate reductase and glutathione reductase were seen in MI over HI. Further, a lower expression of β-cyanoalanine synthase (β-CAS) transcript was associated with decreased cellular β-CAS activity in MI, indicating accumulation of unmetabolized cyanide. TEM studies showed increased gum-resinosis and necrotic cell organelles, which might be attributed to unmetabolized cyanide. In field trials, increased malformed-necrotic-inflorescence (MNI) by spraying ethrel and decreased MNI by treating with ethylene inhibitors (silver and cobalt ions) further confirmed the involvement of cyanide in MMI. Implying a role for cyanide in MMI at the physiological and molecular level, this study will contribute to better understanding of the etiology of mango inflorescence malformation, and also help manipulate mango varieties genetically for resistance to malformation.
Highlights
Malformation of mango inflorescences (MMI) disease causes severe economic losses worldwide
Cyanide is produced during the ethylene biosynthesis pathway in which the enzyme ACC synthase (ACS) catalyzes the rate-limiting step[17,18]; further, increased endogenous cyanide is associated with enhanced cellular ACS activity[19]
Fusarium species have been implicated in malformation, the etiology of this disease remains obscure and effective control measures have not yet been identified[4,11,25]
Summary
Malformation of mango inflorescences (MMI) disease causes severe economic losses worldwide. Β-CAS genes were studied in several plant species[35], there are no reports of β-CAS transcript accumulation and cyanide detoxification in the mango malformation system. The present study aims to study the comparative expression profiles of ACS and β-CAS in malformed and healthy inflorescence (abbreviated as, MI and HI, respectively) of three mango cultivars – Mallika (Mk), Ramkela (Rk), and Langra (Ln) differing in their degree of susceptibility to mango malformation disease. We have used these cultivars to correlate physiological and molecular study with cultivar susceptiblity. Our study attempts to provide insights into the etiology of mango malformation and to help devise strategies to control the malformation of mango inflorescences (MMI) disease
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