The Effect of Hydrogen Cyanamide On Sweet Cherry Floral Organ Development In a Low-Chill Region

The development of a commercial sweet cherry (Prunus avium L.) industry in the Shanghai region of China (and other regions with low chilling accumulation) is limited by inconsistent flowering and low fruit set. Previous research has shown that flower bud differentiation, and pollen development and activity, are normal in the Shanghai region. In attempts to induce more uniform flowering and increase fruit set, the plant growth regulator hydrogen cyanamide (HC) is utilized in low chill regions. The current study was conducted to better understand the mechanism behind poor fruit set in regions with warm winters and the role of HC on floral organ development. We sprayed 2% HC on 5-year-old ‘Hongdeng’ sweet cherry trees cultivated in the Shanghai region (Treated, T). Control trees under similar field management and vigor in both Shanghai (warm winter, CS) and Tai’an City (cold winter region, CT) were studied also. From treated and control trees, 25 flowers were collected every 3 days from 9 February until full bloom. Electron microscopy was used to examine the progression of pollen growth, which was classified into five stages, and observe ovary development, which was divided into seven stages. Chilling accumulation, calculated by 0-7.2℃ chilling model, of T, CS and CT were 525 hr, 810 hr and 1077 hr, respectively. HC-treated in Shanghai exhibited slight differences in the progression of microspore development but great delays in ovule and embryo sac development compared to controls in both locations. In CS, nucellus development stagnated in the mother cell macrospore and macrospore stages in which abortion ratios reached 13%, 15% and 45% at 6, 3, and 0 days before full bloom, respectively. The results indicated that a lack of chilling accumulation was the main cause for abnormal floral organs, and HC treatment accelerated the progression of ovule and embryo sac development.