Use of sunscreen to minimize the effects of environmental stress on photosynthesis and fruiting in citrus trees

• Grant number: 18/18792-4
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: January 01, 2019
• End date: December 31, 2019
• Field of knowledge: Agronomical Sciences - Agronomy - Crop Science
• Principal Investigator: Dirceu de Mattos Junior
• Grantee: Isabela Macca de Franceschi
• Host Institution: Instituto Agronômico (IAC). Agência Paulista de Tecnologia dos Agronegócios (APTA). Secretaria de Agricultura e Abastecimento (São Paulo - Estado). Campinas , SP, Brazil

Abstract

Citrus industry in the state of São Paulo and southern Triângulo Mineiro have suffered crop losses in recent years due to changes in climate, characterized by extreme increase of light radiation and air temperature during critical periods of plant development. It was already estimated that losses in the orchards exceed 30 million boxes (40.8 kg) of oranges in unfavourable years due to the abscission of flowers and young fruits. In this scenario, plant damage is associated with increased in stomatal closure, reduction in photosynthesis and production of assimilates, as well as changes in hormonal balance. Furthermore, under conditions of environmental stress due to high radiation and temperature, plants are subjected to photo-oxidative stress with increasing production of reactive oxygen species (ROS) in the leaves that damage DNA, proteins and membranes. Foliar application of sunscreen-like products (e.g. hydrated aluminium silicates or kaolin) can prevent photo-oxidative damage by reducing leaf temperature, maintaining the stomatal opening and improving plant CO2 assimilation. In addition, kaolin has been shown to be effective in repelling insects, such as Diaphorina citri, which transmits the bacterium Candidatus Liberibacter ssp. causing HLB, whose use should be adopted as a management practice by citrus growers. With the hypothesis that the foliar application of kaolin to citrus leaves under stress reduces the production of EROs, maintains greater assimilation of CO2 and improves fruit set, it is proposed to study its application during the flowering and fruiting period of Valencia orange trees under filed conditions between beginning of the vegetative growth of leaves and the end of the physiological fruit drop. Periodically the development of flowers and fruits, the assimilation of CO2 and chlorophyll a fluorescence, as well as the concentration of chlorophylls and metabolizable carbohydrates in the leaves will be evaluated. The results of the proposed study will allow the estimation of the contribution or limitations of the use of kaolin in young citrus orchards as an important practice for the maintenance of the sanity and productivity of the orchards.