Minimum number of measurements for efficient estimation of black spot resistance in papaya genotypes

Increasing the efficiency in selecting and recommending superior genotypes for black spot resistance in papaya requires proper field evaluation. A randomized block design with six genotypes and four replications was used to evaluate the coefficient of repeatability (r) and the minimum number of measurements. For this, the leaf with early symptoms of black spot (LES), the leaf with incidence of black spot (IBS), and the severity of black spot estimated on fifth leaf (SBS5L) and leaf with axil attached to first open flower (SBSOF) were quantified monthly for nine months. Subsequently, the coefficient of repeatability (r) and the minimum number of measurements (η) were estimated using four distinct methods: ANOVA, PCMCov, PCMCor, and SAMCor. The results suggest that traits IBS and SBSOF have high repeatability, thus requiring fewer measurements (five and three measurements, respectively for IBS and SBSOF) to select black spot resistant papaya genotypes.