Floating Habit of 10 Strains of Wild and Cultivated Rice

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Abstract
The floating habit of 10 strains of rice belonging to Oryza sativa, O. perennis or O. glaberrima was studied by sinking them up to 3 m deep in water at 6 different rates, O (control), 1, 5, 3.1, 4. 6, 62 and 9. 3 cm per day. Number of days of floating, plant height, leaf length, total internode length, number of internodes and average inter-node length were observed. The 10 strains examined were classified into 3 groups regarding the floating habit. Strains 1 and 2 of O. sativa and strain 5 of O. perennis were pronouncedly floating, strains 6 and 7 of O. perennis and strain 8 of O. glaberrima were weakly floating, and strains 3 and 4 of O. sativa and strains 9 and 10 of O. glaberrima were non-floating. Floating habit of individual strains was characterized by 3 factors, a, b and c, which determined a regression of the rate of internode elongation on the sinking rate. Factor a, indicating the rate of internode elongation achieved under normal conditions, was used as an index of resistance against a sudden flood. Factor b represented the slope of the regression line and indicated the capacity of a strain to elongate the internodes in correspondence to water raise. The 3rd factor c indicated the maximum rate of internode elongation. Among the 3 pronounced floaters, strain 1 has an extremely large a and the smallest b, being most resistant against a rapid sinking for a short period. Strain 2 was characterized by the smallest a and c and a much larger b than that of strain 1. Strain 5 has the largest b and c and is most resistant to a chronic flood condition. All 3 weak floaters have only small a and c but their b''s are almost comparable to those of the pronounced floaters.

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