A model of selection and cotton line tests for multi-resistance to diseases and pests is described and discussed. It was adopted by breeders of the Cotton Section of Instituto Agronômico at Campinas, State of São Paulo, Brazil, Fusarium and Verticilllium wilts, ramulosis (Colletotrichum gossypii var. cephalosporioides) bacterium (Xanthomonas campestris pv. malvacearum), nematodes and stem-borer (Eutinobothrus brasiliensis) were considered. Relative resistance indices, appropriate to each adversity factor, and a multi-resistance index are suggested to evaluate the material's performance. Data obtained from 1981 to 1991 are presented. All the resistance indices increased during the period, except for ramulosis, that oscillated around 70% of the corresponding control's resistance. Correlation between the indices of the adversity factors varied on a casual way, around zero, rarely reaching the 5% level of significance. However, in the last years, negative correlations rouse between ramulosis on one side and Verticillium and bacterium on the other. Its importance and consequences are discussed. The average multi-resistance index increased steadily during the period, by 56.7% reaching the final value of 0.776. The value of 1.000 would mean that all the available genes for resistance were added in a same line.
cotton; disease resistance; multi-resistance; Fusarium; Verticillium; ramulosis; Xanthomonas; nematodes; stem-borer