Using chlorophyll fluorometry to compare photosynthetic performance of commercial maize (Zea mays L.) hybrids in the field

The main objective of the present work was to determine if chlorophyll fluo rescence techniques could be used under field conditions to detect differen ces in leaf photosynthetic rates among commercial maize hybrids known to di ffer in agronomic performance. Chlorophyll fluorometry was used to estimate thylakoid electron transport rates (J(e)) in leaves of three commercial ma ize hybrids on 13 days between 48 days after sowing and first frost. The ma ximum quantum efficiency of thylakoid electron transport at low PPFD (phi), and the thylakoid electron transport rate when PPFD absorbed by leaves was equal to 1200 mu mol m(-2) s(-1) (J(e1200)) were estimated using a curve-f itting approach. Canopy absorptance of incident PPFD (alpha(c)) and leaf ab sorptance of incident PPFD (alpha(1)) were measured at regular intervals, S ignificant fluctuations in both phi and J(e1200) were observed over the sea son, and these appeared to be associated with different leaf temperatures o n different measuring days, Measured values of J(e1200) declined in a linea r fashion over the season, but the decline was more rapid in an older hybri d than in two more modern hybrids. All three hybrids could be differentiate d from one another on the basis of J(e1200) measurements in the last part o f the growing season. The two newer hybrids did not differ in their mean cr op growth rates during this part of the season, however, despite the observ ed difference in J(e1200). Regression analyses revealed a strong relationsh ip between mean crop growth rates and alpha(c)J(e1200), supporting the idea that chlorophyll fluorescence can be used to assess photosynthetic perform ance of maize under field conditions. (C) 1999 Elsevier Science B.V. All ri ghts reserved.