Comparison of the sensitivity of the mean and the mode in screening coffee seedlings for resistance to coffee berry disease Colletotrichum coffeanum Noack sensu Hindorf (A short communication)

Summary The utility of the modal grade as an alternative to the mean grade in the pre-selection test for screening seedlings of Coffea arabica L. for resistance to coffee berry disease (CBD) caused by Colletotrichum coffeanum NOACK sensu HINDORF was examined. Three criteria were used to compare the sensitivity of the modal grade with that of the mean grade when partitioning 6 weeks old seedlings into different resistance classes. The criteria were: the sensitivity of the two statistics as estimators of central tendency, the sensitivity of the modal grade and the mean grade as selection criteria and the correlation between the two statistics.The modal grade was neither more sensitive in detecting genotypes that fell in diffent resistance classes nor more severe than the mean grade in screening for genotypes susceptible to CBD. In the cases studied, the modal grad was highly correlated with the mean grade (r_s ranged from 0.55^**–0.82^**). Hence, it is concluded that there are practically no gains in adopting the modal grade as a pre-selection criterion in preference to the mean grade.