Page 153 - FRUTAS DEL TRÓPICO

intRoduction to teRminology and techniques foR studying enviRonmental
physiology of subtRopical and tRopical fRuit cRops 153

rapid change in the intensity of chlorophyll fluorescence takes place. Figure 4 shows a typical
chlorophyll fluorescence pattern immediately after leaf illumination.

Figura. 5. Quantum yield of ‘Hass’ avocado leaves in autumn and winter (from Whiley, 1994).

6 Autumn
A (µmol CO 2 m -2 s -1 ) 2 Ø = 0.055
Winter
4

Ø = 0.034
0

-2

-4
0 20 40 60 80 100 120 140 160 180

-1
-2
PPF (µmol m s )

From this pattern, the maximum to variable chlorophyll fluorescence (Fv/Fm) ratio can be

calculated which is an indication of the amount of damage to the photosynthetic mechanism

(photosystem II) from various abiotic or biotic factors. An Fv/Fm ratio between 0.80 and 0.83
indicates no damage to photosystem II, whereas lower values indicate photoinhibitory damage.

There is a relationship between ambient temperature and photoinhibition. This relationship has

been used to determine optimum climatic zones for some tropical fruit crops such as bananas

and mangos. To do this, detached leaves of different cultivars are held in chambers at different

temperatures to determine at which temperatures there is a significant reduction in the Fv/Fm

ratio. This provides a good preliminary estimation of the temperature range of the species.

Universidad Autónoma de Chiapas