Efficiency of root length phenotypic index in the evaluation of individualmaize plants for aluminum tolerance

The objective of this work was to verify the efficiency of the relative sem inal root length (RSRL) and net seminal root length (NSRL) as phenotypic in dexes for aluminum tolerance in individual maize plants. Seedlings of Al to lerant and susceptible genotypes were grown in nutrient solution containing toxic level of Al for a period of seven days, after which the values of RS RL and NSRL were determined. The results obtained when mean values of RSRL and NSRL were utilized showed that both indexes were able to discriminate t olerant from susceptible maize genotypes. However, when individual values o f RSRL and NSRL were utilized, some tolerant plants scored as susceptible o nes were observed, showing that the phenotypic evaluation of individual pla nts by both indexes is subjected to significant errors, mainly in the chara cterization of susceptible plants. Therefore, in studies for quantitative t raits loci (QTLs) mapping for Al tolerance in maize, where these indexes ar e used, the most appropriate is to use F-3 families, where it is possible t o obtain mean values for RSRL and NSRL and then utilize these means to repr esent the phenotypic values of the respective F-2 plants.