Varietal screening and genetic analysis for iron toxicity tolerance in rice

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Two major field experiments were carried out in Korhogo in Northern Cote d’Ivore, between Sept, 1994 and June 1996 to study the tolerance of rice varieties to iron toxicity. Twenty eight varieties were transplanted into adjacent iron toxic and non-toxic fields. A randomised complete block design was used with three replications. Leaf symptoms of iron toxieity were scored on six occasions during the growing period, using the IRRI scale (1-9). Data were also taken on the number of tillers at the maximum tillering stage, pl4nt height at maturity and grain yield and its components. Iron toxicity symptoms ranged between 2.0 and 7 0. Significant associations were observed between iron toxicity tolerance and reduction in yield (r=0.63**). No such relationship was, however, observed between iron toxicity tolerance and reduction in number of tillers. Scoring for iron toxicity symptoms at 75 days after transplanting (DAT) emerged as the best date for symptom expression. However, a comparison between the highest scores, 75 DAT scores and the cumulative scores (sum of the six highest scores) indicated cumulative scores as providing a more accurate assessment of varietal tolerance. Following the results of the screening trial two groups of populations were derived from crosses between selected tolerant and susceptible parents for genetic studies. Heritability estimates for tolerance to iron toxicity ranged between 25% (in cross II) and 73.57% (in cross I). The genetic analysis showed that the character is probably controlled by a few numbers of genes with epistatic effects, which resulted in heterosis in one of the crosses
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Philosophy in Crop Science, 1997