[Histological studies in the interaction between Coffea arabica and Hemileia vastatrix, involving certain resistant genes]

English. The effect of heterozygosity of the resistance genes SH1 and SH4SH5 in plants of Coffea arabica when inoculated with the same avirulent culture of Hemileia vastatrix was histologically studied. In the coffee tree 128/2 (SH1SH1) the fungus ceased its growth mainly on the first stages of infection giving rise to a reaction of complete resistance (flt). However, in coffee 128/1 (SH1sh1) and in coffee H.168/8 [(849/1 x 128/2) - SH? x SH1], both with SH1 heterozygous, besides the aborted infections (many of them corresponding to flt), others evolved and produced chloroses which sporulated giving rise to an incomplete type of resistance. Of the plants bearing genes SH4SH5 only H.454/43 (SH? x SH4SH5), where genes SH4 e SH5 are both in the heterozygous condition, presented a mixture of resistance (flt) and susceptibility reactions. Callose and lignin were compounds detected in the reactions of resistance. The heat treatment of coffee leaves before inoculation induced an increase in the number of appressoria formed and subsequent colonization of the ression

Portuguese. Estudou-se histologicamente o efeito da heterozigocidade dos genes de resistencia SH1 e SH4SH5 de plantas de Coffea arabica, quando inoculadas com uma mesma cultura avirulenta de Hemileia vastatrix. No cafeeiro 128/2 (SH1SH1) o fungo cessou o seu crescimento predominantemente nas primeiras fases da infeccao originando uma reaccao de resistencia completa (flt). Porem, em 128/1 (SH1sh1) e em H.168/8 [(849/1 x 128/2) - SH? x SH1], ambos com SH1 heterozigotico, a par de infeccoes abortadas (muitas das quais corresponderam a flt) outras evoluiram originando cloroses que em geral esporularam, ou seja, observou-se resistencia incompleta. Das plantas portadoras dos genes SH4SH5 somente em H.454/43 (SH? x SH4SH5), onde para alem do gene SH4 tambem SH5 se apresenta em heterozigotia, se observou uma mistura de reaccoes de resistencia (flt) e de susceptibilidade. A calose e a lenhina foram os compostos detectados nas reaccoes de resistencia. A accao dos tratamentos com calor, pre-inoculacao, traduziu-se num aumento da formacao de apressorios e da subsequente colonizacao do fungo, do que resultou, na interaccao compativel, um aumento de susceptibilidade. Na interaccao incompativel, a maioria das infeccoes conseguiu esporular, sendo tambem de destacar a ausencia de lenhificacao das celulas em resposta a presenca do fungo; verificou-se assim uma inversao na expressao de resistencia