Relationships among Leaf Area Index, Visual Growth Rating, and Sugarcane Yield

Subjective visual growth ratings (VGR) are often used in sugarcane (Saccharum spp.) breeding programs to compare genotype performance quickly and economically. However the relationship between VGR as well as quantitative growth measurements with final yields is not well understood. Data on Leaf Area Index (LAI) and VGR obtained from a 3-yr study were used to determine the relationships among LAI, VGR, and sugarcane yield in tons of cane per hectare (TCH), and also to determine the temporal trend for the relationships of LAI and VGR with TCH across the growing season. Mean LAI increased linearly through the growing season in which data was collected. LAI was poorly related to TCH (r 2 = 0.09-0.18) early in the growing season and there was a rapid improvement in this relationship by mid-season (r 2 = 0.66-0.76), which was maintained through late-season (r 2 = 0.66-0.87). The relationship between VGR and TCH was strongest in mid-season (r 2 = 0.72-0.88) and relatively poorer early and late in the growing season (r 2 = 0.38-0.53). Similarly, there was good agreement between subjective VGR and objective LAI measurements in the middle of the growing season (r 2 = 0.65-0.77) and slightly deteriorated (r 2 = 0.54-0.57) later in the season. Results indicate that subjective VGR