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 fluorescence techniques could be used under field conditions to detect differences in leaf photosynthetic rates among commercial maize hybrids known to differ in agronomic performance. Chlorophyll fluorometry was used to estimate thylakoid electron transport rates (J(e)) in leaves of three commercial maize hybrids on 13 days between 48 days after sowing and first frost. The maximum 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-fitting approach. Canopy absorptance of incident PPFD (alpha(c)) and leaf absorptance of incident PPFD (alpha(1)) were measured at regular intervals, Significant fluctuations in both phi and J(e1200) were observed over the season, and these appeared to be associated with different leaf temperatures on different measuring days, Measured values of J(e1200) declined in a linear fashion over the season, but the decline was more rapid in an older hybrid than in two more modern hybrids. All three hybrids could be differentiated from one another on the basis of J(e1200) measurements in the last part of the growing season. The two newer hybrids did not differ in their mean crop growth rates during this part of the season, however, despite the observed difference in J(e1200). Regression analyses revealed a strong relationship between mean crop growth rates and alpha(c)J(e1200), supporting the idea that chlorophyll fluorescence can be used to assess photosynthetic performance of maize under field conditions. (C) 1999 Elsevier Science B.V. All rights reserved.