Ethylene-mediated modulation of bud phenology, cold hardiness and hormone biosynthesis in peach

Authors: LIU, JIANYANG - Virginia Polytechnic Institution & State University; ISLAM, TABIBUL - Virginia Polytechnic Institution & State University; SAPKOTA, SANGEETA - Virginia Polytechnic Institution & State University; RAVINDRAN, PRATIBHA - National University Of Singapore; KUMAR, PRAKASH - National University Of Singapore; Artlip, Timothy - Tim; SHERIF, SHERIF - Virginia Polytechnic Institution & State University

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2021
Publication Date: 6/22/2021
Citation: Liu, J., Islam, T., Sapkota, S., Ravindran, P., Kumar, P., Artlip, T.S., Sherif, S. 2021. Ethephon-mediated modulation of bud phenology, cold hardiness and hormone biosynthesis in peach. Plants. 10(7). https://doi.org/10.3390/plants10071266.
DOI: https://doi.org/10.3390/plants10071266

Interpretive Summary: Fruit trees naturally undergo dormancy (“rest”) during late autumn into mid-winter. Dormancy coincides with maximum cold hardiness. An ongoing concern for fruit growers is erratic spring frosts that occur after fruit trees exit dormancy and lose cold hardiness. Bloom/ new fruit can be killed thus potentially reducing yield and profit for growers and a stable fruit supply for consumers. Thus, a means to delay dormancy exit is needed. Application of the plant growth regulator Ethephon has been reported to delay dormancy exit, but has some negative side-effects. This study examined the effect of different concentrations of Ethephon applied to peach and cherry trees in autumn on parameters associated with dormancy (including cold hardiness), changes in overall gene expression, and changes in plant-sourced hormones. It was found that 500 ppm (parts per million) applied at 10% leaf fall was most effective for peach trees, but did result in some branch death. Ethephon delayed bloom by nearly two weeks while maintaining cold hardiness; fruit size was relatively unaffected. Cherry was less affected by Ethephon treatment in terms of bloom delay and fruit size. It was also found that Ethephon application altered expression of plant hormone biosynthesis genes and relative concentrations of plant hormones. Surprisingly, the plant hormone jasmonic acid was also affected, indicating that it is involved in bud dormancy and may be a target for future efforts at delaying dormancy exit and bloom. In summary, applications of 500 ppm Ethephon applied at 10% leaf fall in peaches may provide a useful means to delay bloom, thus potentially reducing the effect of erratic spring frosts; the negative effects seem to be outweighed by the positive effects; jasmonic acid synthesis may be a target for delaying bloom as well.

Technical Abstract: Spring frosts exacerbated by global climate change have become a common threat to temperate fruit production. Induction of bloom delay by plant growth regulators (PGRs) has been suggested as an effective frost avoidance strategy. Ethephon is an ethylene-releasing PGR that has been found to delay bloom in several fruit species, yet its application is often coupled with damages to the fruit trees, circumscribing its usage in commercial tree fruit production systems. Little information is available regarding the mechanisms by which ethephon influences bud dormancy progression and bloom in stone fruits. The present study aimed at exploring the effects of fall-applied ethephon on bud phenology, cold hardiness, and hormonal balance throughout the bud dormancy cycle in peach and sweet cherry. Our findings concluded that ethephon could alter several significant aspects of peach bud physiology, including accelerated leaf fall, extended chilling accumulation period, increased heat requirements, improved cold hardiness, and delayed bloom date. Ethephon effects on these traits were mostly dependent on its concentration and application timing, with a high concentration (500 ppm) and an early application timing (10% leaf fall) being the most effective. The hormonal analysis of buds at regular intervals of chill units (CUs) and growing degree hours (GDHs) indicated that ethephon might exert its effects independent of abscisic acid (ABA) levels in dormant buds. Instead, our data signifies the role of jasmonic acid (JA) in mediating budburst and bloom in peach, which also appears subjected to the ethephon treatment. Our findings present a new perspective in interpreting horticultural traits in the light of biochemical and molecular data and shed light on the role of JA in bud dormancy, which deserves further research attention in future studies that aim at mitigating spring frosts.