2007. Rice plant traits dissection for early vigor and competitiveness with Echinochloa phyllopogon (Stapf) Koss.

2007. Rice plant traits dissection for early vigor and competitiveness with Echinochloa phyllopogon (Stapf) Koss.

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Resistance to herbicides in the most important weeds threatens the sustainability of California rice. Weed-competitive rice cultivars could be a low-cost and safe nonchemical addition to an integrated weed management program. Tradeoffs between competitiveness and productivity and inconsistent trait expression could complicate the breeding of competitive rice cultivars. A two-year competition experiment was conducted. Competition reduced average rice yield from 32% to 48%, and watergrass biomass from 44% to 77%. Path analysis suggested that enhancing rice weed-suppressive ability and weed tolerance while minimizing possible productivity tradeoffs should promote early (12 d after seeding) (DAS) growth and light-capture traits followed by moderate growth rates before heading and a vigorous grain filling period. Late-season competitiveness can lower productivity. A second study focused on the identification and interrelationships among traits for early vigor. In a greenhouse two-year experiment, the growth characteristics ofwatergrass and 21 rice seedlings differed after three destructive harvests for growth analysis at 4-5 leaf stage, early and mid to late tillering. Semidwarf rice seedlings had greater growth traits. However, watergrass had later superior growth rates and tallness. Cluster analysis found that vigorous seedling had more leaf area and early tillering. Seedling height was not associated with the clustering of genotypes into high vigor groups. Overall, these results suggest that rice early vigor, as a component of competitiveness, can be enhanced through selection for leafier, rapidly elongating, and highly tillered plants. A third study identified rice QTLs for early vigor and competitiveness. A population of 137 F2 recombinant inbred lines derived from the cross M-202 x IR50 was grown in the field during 2003 and 2004. Phenotyping was performed at 20, 30 and 60 DAS. A genetic linkage map was generated using 180 microsatellite markers. Path analysis was used to clarify the relationships among diverse variables, including molecular markers, in hypothetical cause-effect models. We located about 40 putative genetic loci associated with rice traits related to plant vigor and competitiveness. Results would be useful for using marker-aided selection for identification of genotypes with superior vigor and competitiveness, and for combining these characteristics into a highly productive ideotype  .