Root Morphology of Upland Rice Cultivars Grown Under Aluminum Toxicity.

Although the upland rice has been known by its moderate tolerance to aluminum (Al), the presence of Al in acidic soils may inhibit and compromise the adequate plant growth. However, there are few reports detailing modern cultivars used by Brazilian farmers with respect to their susceptibility to Al toxicity. Therefore, the aim of this study was to evaluate the root morphology of main Brazilians upland rice cultivars grown under Al toxicity. The experiment was arranged in a 2 x 9 factorial randomized complete block design, with four replicates. The treatments were presence and absence of Al in the nutrient solution and nine upland rice cultivars (BRS Monarca, BRS Pepita, BRS Bonança, BRS Primavera, BRS Sertaneja, Maravilha, IAC 202, ANCambará and ANa7007). Plants were evaluated for root length and diameter (WinRhizo 3.8b software - Regent Instruments, Inc., Quebec, Canada); root dry matter. The cultivar BRS Monarca showed higher root dry matter production when cultivated in the presence and absence of Al. The cultivars BRS Pepita, Maravilha and ANa7007 obtained lower root dry matter production when cultivated in the presence and absence of Al. The cultivars BRS Monarca, BRS Bonança and ANCambará showed greater root length when grown in the absence of Al in comparison to the others. On the other hand, it is observed that the cultivar ANa7007 in the presence of Al, despite showing lower root dry matter production, has the greatest root length among all cultivars when grown under stress by Al, so it is a interesting characteristic of a Al tolerant cultivar. The cultivar ANa7007 showed the lowest root diameter in both types of cultivation (absence and presence of Al). The root diameter referring to the cultivation in the absence of Al can be considered as a reference for comparison due to the increment in root diameter caused by Al toxicity. So, comparing the cultivars in the presence and absence of Al, the effect of root thickening favored by the toxicity occurred for almost all the cultivars, except for ANa7007. The cultivar BRS Monarca stands out for the increment of 0.107 mm (average) root diameter, in the comparison of cultivated in the presence and absence of Al, and it was the highest value observed among the nine tested cultivars. Given the presented results, the cultivars BRS Monarca, BRS Bonança and ANCambará obtained adequate growth without the presence of Al and at acidic pH (4.0); while only the cultivar ANa7007 obtained the higher growth when cultivated in the presence of Al.