Physiological responses of developmental flowering stage of cashew tree

Abstract

The cashew (Anacardium occidentale) is one of the major fruit crop in tropical and subtropical region which it can grow well in the Northeast and South of Thailand. To date, very few studies aim to understand the physiology of cashew on the flower induction and development of the cashew fruit. It is known that the flowering process is controlled by both internal and external factors such as temperature, carbohydrate, water stress and nutrition. This investigation was aimed to understand the effect of climatic factors on flower and quality of cashew apple fruits bearing on 6-year-old cashew trees grown in an orchard in Ranong Province, south of Thailand. Cashew trees were divided into three groups as non-flowering, flowering and leafy-buds. Soil and leaf samples were collected on December 9, 2012 and March 9, 2013. Results showed that flowering of cashew began in November to December and anthesis occurred on December with the peak flower blooming on February and May. In December, the peak flowering of cashew, the average of temperature, relative humidity and light intensity during December month was 30.62°C, 87.54%, and 2819.48 Lux, respectively. However, the change in leaf water potential was a consequence of the change of soil moisture. Leaf water potential of cashew trees on December, 2012 ranged from -0.55 KPa to -0.66 KPa. Then, ii decreased to -0.76 KPa to -0.88 KPa of leaf water potential on March, 2013. Although soil pH during December 2012 ranged from 6.33-6.83, soil pH during March 2013 increased to 7.85-8.00. Carbohydrate is one of the internal factors that affects flowering in fruit tree species since it is necessary for growth, regulation of the plant metabolism and development. The total non-structural carbohydrate (TNC) of cashew trees was significantly different between on December 2012 and March 2013, which ranged from 115.08 to 139.56 mg glucose/g dry wt. and 96.69 to 119.36 mg glucose/g dry wt., respectively. In addition, nitrogen plays an important role in flowering because high concentrations of carbohydrates accumulated with low nitrogen cannot promote flowering. The pattern of total nitrogen (TN) in cashew leaves was rather stable on December, 2012 and March, 2013. The TN of cashew leaves ranged from 9.84 to 11.89% on December, 2012 and from 8.99 to 11.32% on March, 2013. However, the highest total nitrogen was found in leaves of flowering cashew tree. In the present study, the change in the C/N ratio was similar to the pattern of change in the TN which the highest C/N ratio (1.17) was found in cashew leaves on March, 2013.