Nagina 22 mutants tolerant or sensitive to low P in field show contrasting response to double P in hydroponics and pots

A simple screening method is needed to identify rice genotypes tolerant to low phosphorus (P) in soil. Nagina 22 (N22) mutants were classified as gain of function (gof) and loss of function (lof) for tolerance to very low P (soil Olsen P 2.01 mg kg(-1)). Two gof and two lof mutants were grown in hydroponics and in pot experiment at three P levels (-P, +P and +2P). Comparing response at +P and +2P in hydroponics we found that shoot and root dry weight were significantly less in gof and significantly more in lof in +2P. In pots with soil, tiller number and yield/plant was 3 fold less in gof but 2.5 to 3 fold more in lof and N22 in +2P compared to +P. That 2P can be used to identify low-P tolerant genotypes was validated using 3 low-P tolerant and 3 sensitive varieties whose response to low P soil is well documented. Both shoot and root dry weight was significantly less in +2P than in +P in tolerant and significantly more in sensitive genotypes. Thus screening in hydroponics in +2P can help identify low-P- tolerant genotypes easily and rapidly avoiding field screening.