Exogenous salicylic acid alleviates high temperature-induced inhibition of flower bud differentiation in red raspberry by modulating anther development and phytohormone homeostasis

Red raspberry ( Rubus idaeus L.) is rich in bioactive compounds, including tannic acid, raspberry ketone, and anthocyanins, making it a valuable resource for the food and health product industries. This study aims to clarify the flower bud differentiation process of the double-season red raspberry ‘Polka’ under high temperature (HT) conditions. It also evaluates the effects of salicylic acid (SA) on plant development, providing a theoretical basis for regulating flowering and fruiting. Differences in soluble protein content, as well as the activities of energy metabolism enzymes, including adenosine triphosphatase (ATPase) and cytochrome oxidase (COD), were determined under different treatments during flower bud development. Indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellic acid (GA 3 ), and zeatin riboside (ZR) were also measured across treatments. Flower bud differentiation of “Polka” followed eight morphologically distinct stages from undifferentiated to pistil primordium formation, which takes about 28 days. Subsequent pollen development was characterized in five phases from the pollen mother cell stage to the mature stage. HT stress at the pollen mother cell stage disrupts tapetum function, leading to defective microspore development and abnormal stamen or anther formation. Reduced IAA, ZR, and GA₃ levels, together with increased ABA, disrupt hormonal balance, thereby inhibiting flower bud differentiation and male gametophyte development. Exogenous SA (150 µmol·L − 1 ) alleviates anther structure damage, enhances microspore formation, regulates hormone balance, promotes protein synthesis and energy metabolism, and improves HT tolerance.