Effects of plant growth regulators on fruit qualities and quality detection in table grapes using Near Infrared Spectroscopy

Abstract

Plant growth regulators (PGRs) have various effects on table grape qualities such as firmness, soluble solids content (SSC), pH, titratable acidity (TA) and especially seedlessness. The conventional method for fruit qualities is sample destructive, cost and time consuming. Therefore, the new method Near Infrared Spectroscopy (NIRS) technique was studied. The experiments were done at aMonsoon Valley vineyard, Prachuab Khiri Khan province and Chaofah vineyard, Chiang Rai province, Thailand. The seeded and seedless treatments were applied with PGRs to the intact inflorescences of ‘White Malaga’ table grapes by soaking. The seeded treatment was without PGR application (Tr.1), while seedless treatments were applied with the first and second application at the 14 days before flowering and flowering stage with either 25 mg/L gibberellic acid (GA3) and the third application was 14 days later on pea stage with 25 mg/L GA3, 5 mg/L cytokinins (CKs) and 1 mg/L brassinosteroids (BRs) (Tr. 2, 3 and 4, respectively). A total of 280 berry samples were analysed. The experimental design is Completely Randomized Design (CRD) with 10 replications and 4 treatments (an experimental unit is 1 cluster). Plant Growth Regulators (PGRs), GA3, CKs and BRs, have effects on table grapes such as fruit qualities and seedlessness. The width and weight of untreated treatment were significantly higher than PGRs treatment, while the length, firmness, TA and tartaric acid were not significantly different. SSC and pH of treatments which applied CKs and BRs were lower than other treatments as a result of late development. The GA3 application has obvious effects on seedless grapes while the BRs treatment yielded seeded grapes. After PGRs application on grape clusters, the expression of certain seedlessness genes was studied but the RNA extraction was obstructed in secondary metabolite. The results showed low quality of RNA which cannot study gene expression in next step. The development of RNA extraction on ‘White Malaga’ table grapes for termination the secondary metabolite needs to be done. Near infrared spectroscopy (NIRS) technique is the non-destructive determination for fruit quality analysis. The interactance mode of wavelength 800-1100 nm. is well suited for evaluating the internal grape quality parameters. Good prediction models were achieved for SSC, seedlessness and TA, and promising results were also obtained for pH-value and firmness. NIRS with suitable chemometric analysis successfully identified seedlessness in ‘White Malaga’ table grapes. The performance of several classification methods was compared. Quadratic Discriminant Analysis (QDA), possessing the predictive ability of linear modelling, provided the best classification results. The development of an NIR-chemometric model could be used to non-destructively detect and quantify the number of seeds in ‘White Malaga’ table grapes. SSOM is a very good technique for classification of the treatments.