Towards a New Ecophysiological Approach to Understand Citrus Crop Yield Under Abiotic Stresses Mirroring in the Brazilian Savanna Genetic Resources

Abstract

Under the threat of unavoidable global warming and its consequences, citrus production has important impacts on water consumption in (irrigated) orchards and nurseries. Knowledge of agriculture indicates that more than 60% of variability in crop productivity may be explained by fluctuations in climate. More than 55% of the causes of crop losses can be identified as soil water deficits. In this context, areas for citrus production in Brazil are located in Sao Paulo and Minas Gerais states, but the most productive regions are the northwestern and the northern regions of Sao Paulo state, where frequent and intense droughts, high air temperatures and vapor pressure deficits occur. In these regions there are more incidences of citrus diseases, such as citrus variegated chlorosis and citrus sudden death. These factors have induced some citrus growers to irrigate their orchards. Field experiments have shown that irrigation may increase citrus production by more than 50% on an area basis, compared to non-irrigated areas. Considering extensive land areas for citrus in Brazil, irrigation systems may become very expensive. Alternatively, citrus groves have migrated to the south of Sao Paulo state, where soil water deficits and air temperatures are low. However, high temperatures enhance citrus growth and fruit production. Thus, the southern region, with approximately 5.5 million new citrus plants, might be interesting for plant water balance and disease attenuation, but not for carbon gain, and consequently, production. In fact, the northwestern and the northern regions were still responsible for the largest production in 2007/2008. To support the citrus industry, with 190 million productive plants, greenhouseand screenhouse-protected nurseries use drip fertirrigation to produce high quality varieties and cultivars of scions grafted on specific rootstocks; screenhouseprotected systems also prevent plants from diseases and their vectors. But there are indications of over irrigation in nurseries, suggesting waste of water. It has also been reported that water may not be a renewable natural resource, and that water consumption is increasing, as the human population enlarges. The original habitat of citrus species is believed to be shaded environments of forest understories in southeastern Asia. On the