Physiological basis and metabolite profiles of pre harvest sprouting resistance in rice varieties of Tamil Nadu

Pre-harvest sprouting (PHS) poses a persistent threat in rice growing regions. Tamil Nadu, is often prone to unexpected rains before harvest, aggravating the PHS. This study aimed to evaluate the genetic variability of PHS in popular rice varieties of Tamil Nadu, assess the effectiveness of chemical treatments and growth retardants in controlling PHS and to understand the underlying mechanisms by profiling metabolites, hormones and enzymes. An extensive field survey identified Coimbatore (CO) and Aduthurai (ADT) varieties as highly susceptible. The newly released varieties CO 55, ADT 56 and ADT 57 exhibited PHS resistance. Various chemicals including sodium chloride, sodium molybdate, glucose, mepiquat chloride, cycocel, ethrel, abscisic acid (ABA) and eugenol were tested as solutions at different concentrations on rice seeds during germination tests to evaluate their ability to inhibit PHS. NaCl @ 10% concentration was most effective, achieving 100% inhibition of seed germination and maintaining seed viability. NaCl treatment significantly reduced alpha-amylase activity (31-59%), further contributing to the inhibition of PHS. Metabolite analysis revealed that, NaCl treatment significantly altered the profiles of carbohydrates, amino acids and polyols. Accumulation of carbohydrates, sugars, amino acids, peptides alcohols and polyols enhanced osmotic adjustment by lowering seed water potential, restricted water uptake and promoted seed dormancy, preventing PHS. Hormone analysis showed increased ABA and decreased GA levels in NaCl-treated seeds, correlating with reduced germination. Foliar application of NaCl @ 10% at 14 days before harvest completely prevented PHS when plants were exposed to artificial rainfall conditions. This study concluded that application of NaCl @ 10% as foliar spray at 14 days before harvest could be an effective treatment for preventing PHS in rice.