Lack of Chill Influences Flower Development and Carbohydrate Content of Pistacia vera Spp.

In 2015, pistachio (Pistacia vera) production in California’s Central Valley dropped by over 50% compared to previous years. Warm winter temperatures and therefore decreased dormant chill were possible factors for the erratic bloom, poor fruit set and resulting low yield. How well pistachio flowers develop in warm winter regions has not been well investigated. Our research is assessing the development of pistachio flower development under low chill conditions. We are assessing both anatomical structures and floral organ activities; i.e. pollen and ovules. The variation of carbohydrate content in proximal twig sections individual flower buds with low dormant chill will also be evaluated. From mid-February, 15 cm twig sections at least 8cm in diameter with more than 3 floral buds/flowers 5 cm apart have been collected from both south and north facing trees canopies in both female (Kerman) and male (Peters) cultivars. Samples from the high-chill orchards are co the control. The biweekly sampling will be continued through fruit set. Twig carbohydrate content will also be measured to determine if chill affects respiration and therefore final carbohydrate content and bloom quality.