Ecophysiological factors related with the vegetative growth, flowering and fruit growth in avocado

Abstract
In this work we analyzed the effect of different ecophyisiological factors on the concentration of carbohydrates, nitrogen fractions, proteins contents and on some stress indicators (abscisic acid, proline, chlorophyll content and chlorophyll fluorescence), with regard to the presence to fruit, and plant response to sprouting, fruit growth and flowering. Experiments were carried out on adults avocado trees (Persea americana Mill.) cv. 'Hass', grafted onto Mexican seedling, located in a commercial orchard in Callosa d'En Sarriá, Alicante, Spain. Treatments involved two radiation levels, three flowering intensities, and the time-course samplings of all tissues from fruited shoots. Results showed, by means of successive defruiting, the period during which the fruit inhibits the following flowering, being the second physiologic abscission the most effective season. The behaviour of the sugars was modified, both by radiation levels, as flowering intensity. Seed showed as a strong sink during the period between the first and the second vegetative growth, accumulating most of the starch in this period. Periods of flowering and first vegetative growth was significantly dependent of the soluble sugars and on the starch accumulated during the period of the second shoot growth. After this period, fruit becomes a significant sink for soluble carbohydrates, which accumulated in its tissues. The carbohydrates with higher relevance during the phenological events studied were gluc-6-P, manoheptulose and perseitol. Fruit ripening was related with a significant decrease of manoheptulose and perseitol. These sugars were identified as translocation sugars in avocado. Gluc-6-P was related with the energy supplied in periods of a high demand. Differences in flowering intensity modified significantly following sprout, buds sprout and following flowering. Fruit absence allowed for a better sprouting and carbohydrates accumulation to sustain next flowering. The second vegetative shoot growth, that is concomitant with the end of the second physiological fruit abscission and the third date of defruiting fruits, showed a significant dependence for photoasimilates synthesized and available during the linear fruit growth stage. The flowering was a strong sink of nitrogen compounds, particularly ammonium, and flowering intensity was inversely and significantly correlated with chlorophyll contents. The ecophysiological stress factors analyzed had a significant effect on next flowering irrespective to the presence of fruit. Chlorophyll fluorescence, proline concentration and abscisic acid (ABA), under conditions of presence or absence of flowering and presence or absence of fruits, were also analyzed. On the other hand, scoring modified the maximum quantum yield efficiency of photosystem II (Fv/Fm), inducing photoinhibition. The radiation also produced a significant effect in the chlorophyll fluorescence parameters, evidencing the photoinhibition light-induced in this species.