Components of resistance of conilon coffee that reduce the rate of leaf rust development

This study aimed to quantify the levels of resistance of 39 hybrids "Clone 83 x Clone 02"of Coffea canephora var. conilon to the races II (v(5)) and XXXIII (v(5,7,9)) of H. vastatrix. To study the resistance of the genotypes, leaf discs were removed from the plants and spreaded on the top of a stainless steel screen inside gerbox as a moist chamber. The gerboxes were mantained at 22 +/- 2 A degrees C in the dark for 48 h and under 12 h of photoperiod, respectively. The hybrids were classified into four levels: resistant (R), moderately resistant (MR), moderately susceptible (MS) and susceptible (S). Leaf discs (%) containing sporulated lesions was the resistance component that had the greatest absolute correlation (0.95). The level of resistance of the hybrids varyied according to the race of the pathogen. The percentage of R, MR, MS and S of the hybrids to race II and XXXIII were 25 %, 25 %, 38 %, and 11 %, and 13 %, 37 %, 42 %, and 8 %, respectively. Nine (25 %) and five (13 %) hybrids were R to race II and XXXIII, respectively. Four hybrids (21, 30, 48 and 66) showed vertical resistance to races II and XXXIII. Possibly these hybrids have the resistance factor S-H6, because they were resistant to race XXXIII v(5,7,9). Leaf discs (%) with sporulating lesions can be used as a reference in future studyies of screening genotypes with horizontal resistance to C. canephora genotypes to leaf rust.