Genetic variation for physiological traits in introgressed hybrids of Saccharum robustum x S. officinarum

Abstract

Sugarcane is an important cash crop and to overcome yield loss due to abiotic stresses, a combined strategy of physiological, breeding and molecular methods is essential to develop varieties tolerant to more than one type of stress. Forty seven introgressed hybrids F1 (25) and BC1 (13) from crosses of S.officinarum (PIO) and S.robustum (PIR) viz., PIR 00-1157 x PIO 00-845, PIO 90-202 x PIR 96-475, SRH 13-92 x Co 0240 and PIR 00-1058 x SRH 13-394 were screened for physiological characters viz., chlorophyll content, nitrate reductase (NR), peroxidase (POX), superoxide dismutase (SOD) activity and total protein during formative FP (120 days) and grand growth phase, GGP (240 days). Leaf chlorophyll content and nitrate reductase activity plays a considerable role in plant metabolism and high significant differences were observed in genotypes for chlorophyll content and nitrate reductase activity. Total chlorophyll in F1 and BC1 hybrids ranged from 0.87-2.09 and 0.81-1.72 mg/gm of leaf and 1.10-2.35 and 0.92-1.93 mg/gm at 120 and 240d respectively. Total protein at FP is 0.161-0.422 (F1) and 0.960-0.405 (BC1) mg/gm of leaf. NR activity at FP varied as 1.21-3.37 (F1) and 0.46-3.18 (BC1) µmoles nitrite/gm/hr. Activity of anti-oxidative stress enzymes viz., SOD ranged 18.00-27.00 units/gm/min and POX 346.00-458.00 units/gm/min. The chlorophyll ‘a’ and chlorophyll ‘b’ at GGP in F1 hybrids was 0.78-1.61 and 0.32-0.73 mg/gm FW of leaf respectively and in BC1 hybrids is 0.62-1.34 and 0.30-0.59 mg/gm FW of leaf respectively. Six hybrids viz., SRH-13-92, SRH-13-105, SRH-13-272, SRH-13-177, SRH-14-415 and SRH-14-572 recorded highest total chlorophyll (GGP) of above 2.00 mg/gm FW of leaf, greater than the mean values of parents. Hybrids of PIR x PIO and PIO x PIR groups had positive correlation for yield (t/ha) with total chlorophyll (r=0.4610 * * and r=0.4017 * * ), NR activity (r=0.4805 * * and r=0.4536 * * ) and total protein (r=0.5756 * * and r=0.5082 * * ) respectively. NR activity was found to be more positively correlated with total protein (r=0.6714 * ) in PIR x PIO hybrids. Overall fourteen hybrids identified with high NR activity >2.50 µmoles nitrite/gm/hr also had high amount of total chlorophyll >1.75 mg/gm, total protein >0.300 mg/gm and also high activity of SOD >30.00 units/gm/min and POX >500 units/gm/min at GGP were high yielding types with moderate quality and showed no natural incidence of smut in S. robustum progenies. The study indicates the potential of these highly metabolically active pre breeding (Back cross) material as donors in breeding programmes to improve photosynthetic rate and for development of clones with resistance to multiple stress factors.