RICE RATOONING - IRRI books - International Rice Research Institute

BREEDING AND TESTING FOR RATOONING ABILITY IN TEXAS 51reserve carbohydrates (total nonstructural carbohydrates [TNC]) in the culms atmaturity with ratoon yield (3). At main crop maturity, subsamples of plants wereharvested from all plots to be ratooned. The panicles were removed, samples driedand ground, and TNC percentage determined.As with ratoon yields, TNC appears to be inherently highly variable. Themean coefficient of variation for TNC ranged from 11.2 to 27.3 among the RegionalUniform Nursery groups in 1977 and from 16.2 to 29.5 in 1978. For all groupscombined, the correlation coefficient between TNC percentage in 1977 and 1978 was0.208, a low but statistically significant value. For the individual groups, thecorrelation coefficients for groups I through V were 0.307, 0.020, -0.493, -0.066, and0.619. Despite the high degree of variability in TNC values, statistically significantdifferences among selections were common in all regional nursery groups in both1977 and 1978. An example of the range in TNC values within a regional nurserygroup is presented in Table 5.Correlations of TNC with main crop yields and ratoon yields in 1977 and 1978are presented in Table 6. Although TNC and ratoon yields correlated significantly insome test groups, the levels appear to be too low to have much practical value as aselection criterion in breeding for superior ratooning ability. Although weintentionally used the simplest approach in our investigation of TNC as a possibleselection index for ratooning, the time required for sample preparation andlaboratory evaluation was probably too great for TNC to ever be developed as aroutine screening procedure. In our opinion, any technique that would requireextensive labor for sampling, sample preparation, and carbohydrate determinationswould limit the number of selections that could be tested to an ineffective level.However, newly developed laboratory equipment, such as near-infrared (NIR)reflectance, might allow almost instantaneous evaluation of carbohydrate levels indried culm samples with minimal cost and labor.Table 5. Average TNC percentage in mature culms of selections in Group I of theRegional Uniform Nurseries, Beaumont, Texas, 1977.Selection(%) TNC aRU7702010RU7502006RU7702003CI 9857RU7701021RU7703008LabelleRU7401011RU7701014SkybonnetRU7603009RU7701001RU7703012RU7601007RU7702016RU7701004Newrex15.4 a12.1 b11.2 b10.1 bc9.6 bcd8.8 bcde7.7 cdef7.1 cdefg6.9 cdefg6.6 defg6.0 efgh5.9 efgh5.5 efgh5.3 efgh4.8 fgh3.82.5ghha ln the column, values followed by a common letter are not significantly differentat the 5% level by Duncan’s multiple range test.