Abstract:
To study horizontal resistance of coffee plants to H. vastatrix quantitative measurements on resistance are necessary. In this paper the results' of some greenhouse and laboratory tests are compared to field observations. Regular field readings -within the Icatu population, using a 6 point scale for disease access, have shown that a continuous variation for resistance exists within this population. Grafts of 55 plants of Icatu have been inoculated in the greenhouse with race I I of the pathogen. Besides readings using the 6 point scale, estimates on sporulation rate and lesion size were made. The results show a good relation between field and greenhouse observations. Lesion size, however, was less correlated with disease incidence since many plants show large chlorotic areas with only sparse sporulation. As a laboratory method detached leaves and leaf disks have been inoculated and maintained at high relative humidity. Conservation of detached leaves was insatisfactory and this method has been subsequentely abandoned. Leaf disks, when placed, on wetted filter paper in petri dishes, stayed green and apparently healthy for even more than 120 days. An inoculation experiment, using a susceptible, moderate susceptible and resistant plant of Icatu, indicates that the rate of infection of the leaf disks could be a promising parameter for quantitative disease assessments. Investigation with other plant material will be undertaken to further determine the effectiveness of this method.
