Breeding Kiwifruit for Enhanced Stress Tolerance: Advances and Challenges

Kiwifruit ( Actinidia spp.) is a valuable fruit crop that faces significant challenges due to various environmental stresses, including drought, salinity, heat, cold, and waterlogging. Recent advances in molecular breeding and functional genomics have identified several key genes and regulatory mechanisms that enhance stress tolerance in kiwifruit. For instance, the R1R2R3-MYB transcription factor AcMYB3R has been shown to improve drought and salinity tolerance in transgenic Arabidopsis plants by upregulating stress-responsive genes. Similarly, the heat shock transcription factor (Hsf) gene family has been implicated in high-temperature tolerance, with specific Hsf genes like AcHsfA2a playing crucial roles. Salt stress tolerance has been linked to various physiological and biochemical adaptations, including increased proline content and enhanced antioxidant enzyme activities. Waterlogging tolerance mechanisms involve complex metabolic and transcriptional responses, as demonstrated by the superior performance of certain kiwifruit genotypes and rootstocks under waterlogged conditions. Additionally, melatonin application has been found to mitigate heat stress by promoting antioxidant pathways. These findings provide a comprehensive understanding of the genetic and molecular bases of stress tolerance in kiwifruit, offering valuable insights for breeding programs aimed at developing more resilient cultivars.