Submitted to: Proceedings of Southern Weed Science Society
Publication Type: Abstract only
Publication Acceptance Date: 1/27/2003
Publication Date: 2/15/2003
Citation: Estorninos, L.E., Gealy, D.R., Baldwin, T.L., Baldwin, F.L., Burgos, N.R. 2003. SIMPLE SEQUENCE REPEATS ANALYSIS OF HYBRIDIZATION BETWEEN IMI RICE AND RED RICE. Proceedings of Southern Weed Science Society. 56:184. Interpretive Summary:
Technical Abstract: Conditions favorable for growing cultivated rice are also favorable for the growth, development, and reproduction of red rice, due to their morphological similarities. Such conditions create a concern for hybridization between rice and its weedy relatives, especially when the rice cultivar is herbicide-resistant. Our objectives were to determine the incidence and rate of hybridization between imidazolinone-resistant (imi) rice lines and red rice. Experimental fields that had been seeded with red rice and the imi rice lines, CF2551 (CL121), CF3291 (CL141), or CF0051 in 2000, were sprayed with three imazethapyr applications in 2001 to kill susceptible plants. The predominant red rice in these fields was a strawhull, awnless type, but others were also present. The estimated initial red rice population in each field (91.5 m by 30.5 m) in 2001 was 3.7 million plants, but this could be greater or less than the number of red rice seeds actually produced in the 2000 crop. Numerous volunteer imi rice plants survived the imazethapyr applications. Genomic DNA was extracted from mostly non-volunteer survivors. Of the 305 such survivors in CF2551 plots in which red rice and rice had flowered synchronously, 168 plants were considered probable F1 hybrids. This determination was based on the presence of pubescent leaves (dominant trait) and DNA fragment sizes that were consistent with both imi rice and strawhull red rice for one or more of the SSR markers, RM215, RM234, RM251, and RM 253. By contrast, only 85 such survivors were present in CF3291 plots in which rice flowered several weeks after red rice, and only 50 of these were probable F1 hybrids. Similarly, 50 probable F1 hybrids were detected from 180 survivors in CF0051 plots in which flowering of rice and red rice overlapped slightly. Thus, estimated outcrossing rates between CF2551, CF3291, and CF0051 imi rice and red rice can be calculated as 0.0045% (e.g. 168/3.7 million), 0.0014%, and 0.0014%, respectively. In addition to the probable F1 hybrids, numerous heterozygous imi survivors produced DNA fragment sizes that were not consistent with imi rice or strawhull red rice, or else produced glabrous leaves. These individuals could not have been F1 hybrids from homozygous imi rice with glabrous leaves (recessive trait) and strawhull red rice parents with pubescent leaves, but they could have resulted from crosses between heterozygous parents or from pre-existing red rice hybrid derivatives (e.g. F2, F3, etc.) or from other Oryza germplasm lines present in soil at these experimental field sites. Although small numerically, the levels of hybridization reported here may result in hundreds or thousands of plants per field depending on the level of red rice infestation.