2017 ASHS Annual Conference

Spring frost is one of the most unpredictable cropping factors in many peach production areas. A severe spring frost can wipe out an entire peach crop whereas a mild spring frost may naturally help thinning as is common practice in commercial peach production. The extent of frost damage depends on the duration and climate of freezing temperature, and also varies from peach genotypes. Deeply frozen buds, flowers and/or fruitlets will dry out and abscise shortly. Low-chill cultivars in corresponding areas bloom earlier than higher chill cultivars and are generally more vulnerable to frost damage. A severe spring frost on 29 Mar. 2015 after three weeks of bloom dramatically reduced fruit set and resulted in many buttons (abnormally small fruit with dead embryos), which also provide a chance for morphological observation on frost affected peach fruit and genetic perspectives of buttoning. The fruit set rating was different in 2014, 2015, and 2016, averaging 5.61 in 2014, 2.61 in 2015, and 6.04 in 2016, on a scale of 0 to 9. Frost damaged fruitlet buttons and skin-damaged fruit in 2015 varied among peach genotypes. Comparison of fruit and button set rating showed some significant differences in fruit set for four ripening months, among the three years, and among the nine chilling classes, respectively. Among the cultivars, the most common button set rating was 0-3. In the population derived from a cross of button-prone selection and button-free selection, fruit and button counts from ten shoots ranged from 4 to 53 fruit and 2 to 27 buttons, respectively. The peach button rate ranged from 5.4% to 87.1%. The range, distribution, and percentage of the button counts suggested that, if buttoning was genetically controlled, it was likely inherited quantitatively. A healthy fruitlet affected by spring frost had four outcomes: dropped fruitlet, small button, normally-sized but skin-damaged fruit, or normal marketable fruit. Quick fruitlet drop was primarily due to a freezing injury to the entire fruitlet, including skin, flesh, pit, and embryo tissue. Button or normally-sized but skin-damaged fruit could develop if frost damage caused only embryo abortion or skin micro-fracture, respectively. A frost tolerant peach would need to minimize loss to the first three outcomes.