Assessment of cultivated and wild, weedy rice lines to concurrent changes in CO concentration and air temperature: determining traits for enhanced seed yield with increasing atmospheric CO.

Although several studies have examined intra-specific variability in growth and yield to projected atmospheric CO2 concentration, [CO2], few have considered concurrent increases in air temperature and [CO2], and none have compared the relative responses of cultivated and wild, weedy crop lines. In the current study we quantified the growth and seed yield response of three cultivated ('Rondo', 'Clearfield 161', 'M204') and one wild (red) rice line ('Stuttgart-S' or 'Stg-S'), grown at ambient or +200µmolmol-1 [CO2] at one of three day/night temperatures (29/21, 31/23 or 33/25°C). Averaged among all cultivars, [CO2] increased biomass and seed yield, but conversely, increasing air temperature reduced the [CO2] response of both parameters. Among the cultivated and weedy rice tested, 'Rondo' and 'Stg-S' showed significant increases in aboveground biomass and seed yield with elevated [CO2] at 29/21°C; however, only 'Stg-S', the weedy rice line, demonstrated a significant increase with [CO2] at all growth temperatures. A regression analysis for this line indicated that the relative increase in seed yield with [CO2] and air temperature was positively associated with panicle and tiller number, but negatively correlated with the percentage of immature seed. An analysis of all lines indicated that the ratio of tiller production between CO2 treatments at 30 days after sowing (DAS) was a significant predictor of seed yield response to increasing [CO2] for all temperatures. These results suggest that: (i) inclusion of wild lines may broaden genotypic or phenotypic variation and assist in selection to temperature/[CO2]; and (ii) early differences in tiller formation may be an effective means to facilitate screening for CO2 sensitive rice genotypes.