This paper aimed to evaluate the occurrence of favorable environmental conditions for induction of sweet orange flowering in the State of São Paulo, considering as induction factors the low temperature, given by the number of chilling hours below 13ºC (NCH), and the water deficiency accumulated during June, July and August (DEF W), given by the climatologic water balance. Calculations and estimatives were done using the maximum and minimum daily air temperature, as well as the daily rainfall recorded in the last 5 to 14 years, according to the local. There were considered areas in important regions of citrus production, where plantings are in expansion or in potential areas for citriculture, being: Barretos, Bauru, Botucatu, Catanduva, Itapetininga, Itapeva, Jaboticabal, Jaú, Limeira, Lins, Matão, Mococa, Ourinhos, Piracicaba, São José do Rio Preto and Votuporanga. Excepting Botucatu, Itapetininga, Itapeva and Ourinhos, where the flowering induction is triggered by low temperature, water deficiency is the principal factor for induction in other locals. At Jaú, Limeira and Piracicaba the flower induction is caused by both factors. The influence of NCH on flowering induction is more variable when compared to DEF W. In 1996, 2000 and 2004, NCH was higher than 300 h in most of evaluated locals, even in areas where low temperature is uncommon, e.g. Barretos, S. J. Rio Preto and Votuporanga. In relation to the water deficiency, most of the regions showed this kind of environmental influence during the evaluated period, being lower occurrences observed in Itapeva and Itapetininga (54.5 and 72.7% of years, respectively). Unusual situation occurred in 2004, when water deficiency varied from weak (10<DEF W<30 mm) to moderate (31<DEF W<69 mm) in most of the locals. Concluding that DEF W is the main environmental variable during the period of flowering induction in sweet orange plants in the Central-North region of the State of São Paulo, while NCH is predominant in the Central-South region of the State, having influence of both environmental factors in the Central region.
Citrus; cold; drought; ecophysiology
