CLASSIFICATION OF BRAZILIAN WHEAT CULTIVARS FOR ALUMINUM TOXICITY IN ACID SOILS

Aluminium (Al) toxicity is an important limiting factor for wheat Trit icum aestivum L. adaptation to acid soils in different regions of Braz il. The purpose of this research was to classify the reaction of recom mended wheat cultivars in Brazil in relation to Al toxicity. Seventy-f ive cultivars were tested from 3 to 15 years under field conditions fr om 1980 to 1995 in Passe Fundo, Brazil. Soils with pH between 4.2 and 4.9 contained from 2.50 to 4.27 cmol Al/l. The resistance to aluminium in acid soil was evaluated visually before heading time in some years and at maturity in all pears in three replications, using a score ran ging from 0.5 (highly resistant) to 5 (highly susceptible). Using the over-years mean index, 19 cultivars were classified as resistant, 33 a s moderately resistant, 17 as moderately susceptible, and six as susce ptible. The cultivars 'BH 1146','Embrapa 15','Embrapa 24','Embrapa 49' , 'IAC 5-Maringa','IAC 18-Xavantes',`IAC 27-Pantaneiro', 'IAPAR 46, 'I APAR 53','RS 8-Westphalen', Trigo BR 15', 'Trigo BR 20-Guato', 'Trigo BR 25','Trigo BR 35', and 'Trigo BR 41-Ofaie' were the most Al resista nt of the 75 tested. It is highly probable that all Brazilian Al-toler ant cultivars have a major gene known to be on the long arm of chromos ome 4D. Aluminium tolerance was traced by pedigree analysis to a small number of landraces introduced and grown in Brazil in the early twent ieth century. Breeding for resistance to Al is required because soil a melioration by liming is effective only in the upper root zone and sus ceptible or moderately susceptible cultivars do not develop extensive root systems and suffer under drought or hear stress.