MSc

Three lines tolerant to iron toxicity [L1: Mo 19 (Krishnanjana), L2: PTB 53 (Mangala Mahsuri) and L3: PTB 57 (Swetha)] were crossed to six high yielding testers [Tl: PTB 43 (Swarnaprabha), T2: PTB 49 (Kairali), T3: PTB 39 (Jyothy), T4: PTB 45 (Matta Triveni), T5 : IR 64 and T6: Triguna] in a line x tester mating design resulting in eighteen hybrid combinations. Observations taken on yield and yield attributes were statistically analysed to deduce the nature and extent of variability and association among yield and yield attributes, estimate the genetic parameters, assess the combining ability effects and quantify the magnitude of heterosis in hybrid.
Wide variability was found to exist among parents and hybrids for yield and most yield attributes studied indicating ample scope for improvement through selection. Variability among genotypes was low with respect to total number of roots, manganese content in old leaf, total tillers/plant and productive tillers/plant. High heritability coupled with high genetic advance as per cent of mean were observed for grain yield, visual scoring for iron toxicity, iron adsorbed on root surface, iron content in root, iron content in third leaf from tip, youngest fully open mature leaf, oldest leaf, days to fifty per cent flowering, plant height, culm length, panicle length, spikelets/panicle, grains/panicle and shoot weight indicating that substantial improvement in the expression of these attributes over base population can be expected through selection.
Results emphasized that an improvement in days to fifty per cent flowering at tillering and flowering, panicle length, seed set per cent and root weight at maturity are reliable predictor variables for increased yield and tolerance to iron toxicity. Negative selection for traits viz., dry weight of roots, manganese content in third leaf and youngest fully open mature leaf at tillering and flowering, may also lead to simultaneous improvement of grain yield and tolerance to iron toxicity.
Higher estimates of GCA variance over SCA variance indicative of preponderance of additive gene action was evident in case of plant height, culm length, panicle length, seed set per cent, shoot weight and root weight at maturity. Pre-ponderance of non-additive gene action indicated by higher SCA variances than GCA variances was registered for traits spikelets/panicle, grains/panicle, thousand grain weight, root length, visual scoring for iron toxicity symptoms and grain yield.
Evaluation of parents for yield alone based on both mean performance and gca effects revealed L2 (PTB 53) and L1, (Mo 19) to be promising, while, parents L2 (PTB 53), L3 (PTB 57), T1(PTB 43), T2 (PTB 49), T3 (PTB 39) and T4 (PTB 45) were found promising for tolerance to iron toxicity. Scoring of the gca effects and mean estimates for all the yield and yield attributes revealed that, line L2 (PTB 53) followed by line L3 (PTB 57) were the most promising parents. Hybrid H13 (PTB 57/PTB 43) was found to exhibit 'Resistance' reaction to iron toxicity indicating high tolerance to iron toxicity whereas hybrids HIO (PTB 53/PTB 45) and H17 (PTB 57/IR 64) with high mean grain yield were found to be moderately susceptible to iron toxicity. Based on the scoring of estimates of heterosis, sca and mean performance for yield and yield attributes, hybrids, H7 (PTB 53/PTB 43), HIO (PTB 53/PTB 45) and Hl6 (PTB 57/PTB 45) ranked the best. Hence, attempts to identify promising segregants with high yield and tolerance to iron toxicity from these cross-combinations may prove fruitful.
Performance of the genotypes (30th day after sowing) in the laboratory screening revealed that, a drastic reduction in shoot length, total number of roots, vigour index (SL/RL) and biomass was found to occur at 600 ppm, while, root length, number of fresh roots, iron adsorbed on root surface and visual scoring for iron toxicity tolerance (susceptibility to iron toxicity) was found to increase with increase in iron level. Parental line L3 (PTB 57) was the least affected perceptibly by the change in iron level followed by Line L1, (Mo 19), tester T6 (Triguna) and check C2 (PTB 30). Considering the performance of the genotypes for all the attributes at varying levels of iron, it was revealed that check variety C2 (PTB 30) was least affected by higher levels of iron. Among parents, tester T 6 (Triguna) and T3 (PTB 39) and line L1, (Mo 19) were also found to be less affected by varying levels of iron.
Ample variability among genotypes for yield, tolerance to iron toxicity and other yield attributes as evident in the study indicate ample scope for isolation of superior genotypes through concerted breeding programmes.