Estimating Heat Requirement for Flowering in Peach Germplasm

Bloom date (BD) in peach is determined by the dynamic relationship between chilling (CR) and heat requirement (HR) fulfilment during dormancy. Understanding these thermal requirements would enable breeders to adapt new cultivars to variable climates. Among the three traits, HR is the least investigated, with the genetic variability in peach germplasm and interaction between HR, CR and BD still mostly unknown. Therefore, we investigated the HR of 136 peach cultivars over 8 growing seasons (2014–2021) by calculating the growing degree hours (GDH) from the moment their CR was satisfied until full bloom. The HR ranged from 1362 to 10,348 GDH across years and cultivars, with cultivar HR eight-year having the best linear unbiased prediction (BLUP) values from 4808 to 7721 GDH. In addition, a high positive correlation between BD and CR, a negative correlation between CR and HR and a seasonal effect on the correlation between BD and HR were observed. Moreover, simulating HR with different threshold base temperatures (Tb) revealed different trends of GDH accumulation, suggesting that genotype-specific Tb should be determined to allow precise discrimination of this requirement. Peach germplasm showed high variation in HR that could be used in breeding for bloom delay to adapt to different environments and climate change.