Differential grain quality responses of rice varieties under combined salt, cadmium and arsenic stresses

Rice production, a cornerstone of universal food security, is increasingly threatened by abiotic stresses. Among these, heavy metals and salinity have emerged as particularly severe constraints, significantly reducing yield potential and compromising grain quality. Owing to the limited understanding of the synergistic effects of these stresses, the grain quality in genetically distinct rice varieties from two key rice growing countries: Pakistan (Super Basmati [SB], Kala Shahkaku 282 [KS]) and Sri Lanka (Ambalanthota AT 362 [AT], Bathalagoda BG 94/1 [BG])was assessed. All the varieties were subjected to optimized concentrations of abiotic stress treatments like, salt (S; 150 mM NaCl), cadmium, (CD; 300 µM CdCl_₂), arsenic (AS; 250 µM Na_₂AsO_₃), and their combinations (COM, S + AS, S + CD, CD + AS). The head rice yield was significantly reduced to 40-45% in KS and AT under combined stress, whereas the degree of milling increased to 42% in AT under combined stress. Among physical traits, average length (r = -0.90) and arithmetic mean of grain (r = -0.83) showed very strong negative correlations with sphericity, while L/B ratio (r = -0.92) exhibited a very strong negative correlation with aspect ratio. High susceptibility was observed in SB and BG for cooking and functional property traits. An increase in volume expansion from 1.6 to 4.5 cm³ and an elongation ratio 1.30 were observed under AS treatments in SB whereas COM increased elongation ratio to 1.35 in BG. Amylose content was strongly reduced by S + CD treatment to 8 mg/ml but increased to 40 mg/ml by S + AS compared with the control value of 30 mg/ml. Gel consistency in BG was also altered, shifting from soft (120 mm) to hard (30 mm) by COM, S + CD, S + AS, CD + AS compared with individual stress. Our study demonstrated that heavy metal and salinity stress differentially impaired the grain quality in economically significant rice varieties. Overall, KS displayed the notable stress tolerance and adaptability, while combined stress emerged as the most damaging treatment for grain quality parameters.