Relationship between 2-acetyl-1-pyrroline and aroma in Uganda rice populations with Oryza (barthi, glaberrima and sativa) backgrounds

Abstract

The sweet popcorn aroma conferred by 2-acetyl-1-pyrroline (2AP) is a highly economic trait of rice grain attracting premium price worldwide. This research study was conducted to determine the levels of 2AP in Ugandan rice lines with the aim of establishing a better understanding on the level and classes of 2AP and aroma phenotype. Concentration of 2AP was assayed using two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOF-MS) in tandem with sensory evaluation. Substantial variations in aroma intensity within and between the Uganda rice families were recorded. However, the levels of aroma variation were strongly influenced by the type of rice, and the breeding population it was derived from. Hence, three aroma based categories, namely, nonaromatic, moderately aromatic and highly aromatic were identified. GC with complementary sensory evaluation suggested a highly complex nature of rice aroma, as several rice lines were reclassified on the basis of this study. The 2AP contents and aroma intensity for genotypes with O. glaberrima were low compared to O. sativa and O. barthi. Genotypes of Supa 5, Supa 1052, Yasmin aromatic and MET 3 contained high 2AP levels whereas MET 16, MET 6, AGRA 78, AGRA 55, AGRA 41 and Sande TXD 306 exhibited moderate 2AP contents. Therefore, in developing an optimal breeding strategy aimed at improving the aroma in rice, quantitative information about 2AP and complementary sensory evaluation are a prerequisite.

Allelic variations in aroma gene in cultivated rice varieties

“…Sensory evaluation revealed that 23 accessions were aromatic (Table 4); while 33 accessions were non-aromatic, and further subdivided the accessions into three distinct groups of accessions depending on the strength of the aroma perceived by the panelist (Table 4). This result is in agreement with Ocan et al (2019) who also found differences in the strength of aroma among aromatic rice varieties. The strength of aroma is known to be influenced by cultivation condition such as temperature (Prodhan et al, 2017), Light intensity (Mo et al, 2015), plant nutrition (Lei et al, 2018) Figure 1.…”

“…Secondly, analysis of aroma in the grain using gas chromatography by measuring the amount of 2-Acetyl-1-Pyrroline (2AP), a compound that is responsible for aroma (Maravel et al, 2010;Daygon et al, 2017;Ocan et al, 2019). Finally, using DNA markers linked to aroma trait and Functional markers that target the polymorphism that define the functional and non-functional alleles of the aroma gene (Bradbury et al, 2005b).…”

“…For a breeding programme to be successful, it is important to have prior knowledge of the phenotypic and genotypic characteristics of important traits in the available germplasm. Attempts have been made to assess the aroma panel of some accessions using sensory methods and gas chromatography (Kanaabi et al, 2018;Ocan et al, 2019), but the genetic basis of aroma in these and other accessions have not been comprehensively established. The objective of this study was thus to evaluate the aroma status of 56 rice accessions and to assess for the various alleles of badh2 gene using functional markers.…”

Volatile Organic Compound Based Markers for the Aroma Trait of Rice Grain

“…Overall mean abundance of VOCs, representative of previously established non-aromatic and aromatic rice lines (Ocan et al, 2019), were subjected to the Student's T-test at 5% significance level using Genstat software 18 th Ed. (VSN International, Hemel Hempstead, UK).…”

“…With regard to Uganda, several rice germplasm were found to exhibit substantial variations in 2-AP abundance and most significantly, within similar aromatic categories (Ocan et al, 2019). The implication being that the substantial intra-group variations are most likely due to other VOCs, besides 2-AP, substantially contributing towards the rice aroma (Cho et al, 2013;Sansenya et al, 2018).…”