Predicting chilling requirement of peach floral buds using electronic nose

Abstract

Chilling requirement is an important agronomic trait of peach and other deciduous fruit trees. It is a quantitative indicator of natural dormancy and its release in a low temperature environment. It is directly related to the distribution area of fruit trees and the success of cultivation. Therefore, chilling requirement evaluation is very important for cultivar breeding and plant introduction. The existing evaluation method has obvious disadvantages such as harsh conditions, complex operation and time-consuming, which greatly prolong the evaluation process. Chilling requirement of peach floral buds could be quickly estimated by a portable E-nose (PEN3.5). The ratio R of the actual accumulated chilling hours during any period of the dormancy and release process to the chilling requirement was used to indicate the stage of chilling accumulation. 5 stages were set as the R value was 0 (StageⅠ), 0.4 (Stage Ⅱ), 0.8 (Stage Ⅲ), 1.0 (Stage Ⅳ) and 1.2 (Stage Ⅴ). Volatile compounds from the floral buds of 9 cultivars with known chilling requirements at the five stages were tested, and the signals of 10 types of sensors were different. Broad-methane gradually decreased during the dormancy process, and reached the bottom at dormancy release, with a significant difference in each stage (p<0.05), while it increased significantly after dormancy release (p<0.05). The sulphur-organic compound showed a significant decrease in the early and mid-term of dormancy (p<0.05), while stayed in relatively high content during and after the release (p<0.05). Methane-aliph slightly increased during the dormancy and reached the highest content at dormancy release, which was significantly different from that in the initial period of dormancy (p<0.05), and significantly decreased after the dormancy was released (p<0.05). So the three types of compounds could be used as the metabolic markers for different stages of dormancy and release. PCA and LDA analysis indicated that the 5 stages could be clearly distinguished. PLSR analysis was performed on the R value and volatile compounds content indicating by the response of sensors, and the quantitative model was established. Cultivars with different chilling requirements were used to validate the model, and it was found that there was no significant difference between predicted chilling accumulation and chilling requirement estimated by traditional method (p>0.05). It proved that the model established in this paper can be used to evaluate the chilling requirement of peach floral buds. This is the first time that E-nose detection and PLSR quantitative analysis model are combined to be used in the estimation of chilling requirements and have achieved efficient and convenient evaluation. It has a high potential to be applied in the evaluation of peach chilling requirements in the future. And for other deciduous fruit trees or plants, the innovative method is of great reference significance.