HARVEST INDEX FOR STENOCEREUS THURBERI FRUITS (PITAYA) FROM SONORAN DESERT BASED IN SKIN COLOR DETERMINATION

摘要

With the goal of developing an harvest index (HI) objective, easy to implement and non-destructive for Stenocereus thurberi fruits (pitaya), we sampled fruits with 10, 20, 30 and 40 days after flowering (DAF). Fruit skin color determination was done using a Minolta Chroma Meter CR-300 set in the L{sup}*, a{sup}* y b{sup}* color space. Statistical analysis were done based in a complete randomized sampling design by one-way variance analysis and Tukey's test (α=0.05). Pearson coefficient was used to measure the intensity of association between the different variables. The prediction model for DAF was developed with the stepwise procedure using forward selection, considering the determination coefficient (r{sup}2) and Mallows (Cp) coefficient as indicators of model prediction's efficiency. We used the group of variables in linear, quadratic and linear associations either alone o in combinations of two groups. The best model developed includes the L{sup}*, a{sup}* y b{sup}* values in linear form with r{sup}2=0.538 and Cp=4 (DAF = 83.03 + (-0.75*L) + 0.33*a - 1.05*b). We concluded that the determination of skin color using the color space L{sup}*, a{sup}* and b{sup}* can be used as an objective, easy to use and non-destructive HI for pitaya fruit.