Melhoramento do algodoeiro no Estado de São Paulo: obtenção da cultivar IAC 21

It is described the program to obtain cotton cultivar IAC 21 developed over the period of 1981/82 to 1993/94. The cultivar IAC 21 was originated from selections in 'IAC 19' population using the pedigree procedure taking into account some agronomical characteristics, and complemented with two specific breeding cycles for resistance to Colletotrichum gossypii var. cephalosporioides and to nematodes. Initially, comparisons of results were made to 'IAC 19', later to 'IAC 20'. Economical characteristics of production, fiber quality and multiple resistance to diseases (Fusarium wilt, Verticillium wilt, bacterial blight, ramulosis and nematodes) were evaluated. When compared to 'IAC 19', the cultivar IAC 21 showed the following overall gains: 6.2% in yield, being of 18.1% on highly infected soil; 4.6% in seed yield; 2.4% in fiber tenacity and 6.9% in yarn tenacity, with no losses in other characters except to fiber that was lowered by 2.6% (about 1% in absolute value). There was an improvement in Fusarium wilt and ramulosis resistance, and no changes as to resistance to other diseases. A preliminary study revealed that the new anomaly called, in Brazil, "murchamento avermelhado" (reddish wilt or bronze wilt) affected 'IAC 21' more than the resistant cultivar CNPA ITA 90. By its advantages over 'IAC 19' and 'IAC 20', the cultivar IAC 21 was released in 1993, recommended for all the cotton areas of the State of Sao Paulo, except those where "murchamento avermelhado" occurred.