2018 ASHS Annual Conference

Premature flowers, uneven bud break and poor bloom synchrony were observed in pistachio due to the lack of chill in warm winters. Previous research demonstrated warm temperatures (>45 ^oF) during dormancy increased shoot respiration and consumption of carbohydrates. To understand this better, we compared the flower bud development and carbohydrates levels of ‘Kerman’ and ‘Peters’ pistachio trees under low (400 chilling hours) and high (800 chilling hours) winter temperatures. The buds, and shoot sections that 5cm beneath the individual buds were collected biweekly from February through April in 2016 and 2017. The soluble sugar and starch content of the shoot’s phloem and xylem were tested. Results demonstrated that with low chill both male and female flowers bloomed more slowly than flowers that experienced high chill. Consistently, the carbohydrate contents of shoots receiving low chill were significantly lower than the carbohydrate contents of shoots that had received more chilling. At bloom flower buds with high chill had a higher sugar content and produced better bloom than buds with low chill. This data suggests warmer temperatures promoted respiration that exhausted the shoots’ carbohydrates that support bloom.