Portable chlorophyll meter (PCM-502) values are related to total chlorophyll concentration and photosynthetic capacity in papaya (Carica papaya L.)

This study was carried out to verify the practical use of the portable chlorophyll meter-PCM502 (PCM) in two papaya cultivars with contrasting green coloring of the leaf blade (‘Golden’: yellowish-green; ‘Solo’: dark green). The relationship was studied between the photosynthetic process and leaf nitrogen concentration, chlorophyll concentration and SPAD readings. The Portable Chlorophyll Meter (or SPAD meter) is a simple, portable, accurate, fast and inexpensive tool. Two Carica papaya L cultivars were grown in a greenhouse with 30 % interception in the photosynthetic active radiation (PAR). At 90 and 100 days after sowing (DAS), two groups of leaves from each cultivar were used for experiments. One group was considered as “young” leaves (3rd or 4th leaf from the apex) and one group as “mature” leaves (6th or 7th leaf from the apex). In these experimental conditions the following parameters were measured: net photosynthesis, Fv/Fm (potential maximal quantum yield of PSII), total chlorophyll concentration and leaf organic nitrogen. At SPAD values lower than 20 for ‘Golden” and 30 for ‘Solo’, the Fv/Fm ratios were correlated with the increase in the ratio as determined by the PCM. There were cultivar differences related to N allocation in the leaf. ‘Golden’ partitioned significantly less N to chlorophyll synthesis than ‘Solo’ at equivalent leaf N concentrations. This explains in large part the yellowish green leaf coloring of ‘Golden’ papaya. These cultivar differences in chlorophyll concentration were measurable with PCM technology. In contrast, at SPAD values <30 ‘Sunrise Solo’ had a greater rate of Fv/Fm decline than ‘Golden’ indicating that ‘Sunrise Solo’ was more sensitive to damage to PSII when N was limiting. At 90 and 100 days after planting, and with adequate water availability, PCM technology was able to evaluate the total chlorophyll molecules and maximum efficiency of PSII, meaning that the equipment can be used to diagnose physiological alterations related to N metabolism.