การศึกษาลักษณะทางพันธุกรรมและฟีโนไทป์ของลักษณะคุณภาพเมล็ดข้าวเหนียวพื้นเมืองที่สูงของไทย

Abstract

Glutinous rice landrace is widely cultivated and consumed in the highlands of the upper northern and northeastern regions of Thailand. Local sticky rice is used in various ways, including religious ceremonies, as the primary ingredient for fermenting liquor or local wort, and for processing into glutinous rice flour used in making desserts. Glutinous rice landraces generate more income for local farmers. Moreover, glutinous rice landraces exhibit highly diverse genetic characteristics, making them suitable as genetic sources for breeding high-quality glutinous rice. The quality of cooking is a crucial factor in the selection of rice varieties for consumption and use by farmers. The future of rice breeding is focused on developing rice varieties that not only increase yield but also offer superior grain quality compared to traditional varieties. This research aims to evaluate the morphological and agronomical characteristics in glutinous rice landraces. Including, cooking quality of glutinous rice. It also involves studying differences in the nucleotide sequences of genes associated with cooking quality. The study was conducted on two glutinous rice varieties from the highlands of Thailand: Pa Ai Khu Pe (PAKP4 and PAKP5) and Kao Haw (KH2 and KH5), which were compared with the glutinous rice varieties RD 4 (Hard rice) and RD 6 (Soft rice) The study was divided into three parts. The first part aimed to determine the morphological and agronomical diversity of four glutinous rice landrace populations grown in three pots with a 30 cm diameter. The plants were assessed for 22 characteristics, including agronomical traits. The diversities within the population were identified in two categories: plant type and panicle exertion. There was no variation observed within or between populations in the following characteristics: leaf blade color (green), leaf sheath color (green), node and internode color (green), apiculus color, stigma color, stigma exsertion, stamen length, husk color, and spikelet awning (absence of awning). However, variations were found between populations in pericarp color and agronomical characteristics. Statistically significant differences were observed among the glutinous rice populations in terms of the day of flowering, tillers per plant, panicles per plant, spikelets per plant, percentage of felted grains, and 1000 grains weight. Pa Ai Khu Pe exhibited the highest yield. Additionally, the evaluation of glutinous rice grain characteristics revealed that most of the grains were of the large type, with the exception of KH2, which was of the slender type. The second part aimed to determine the cooking quality characteristics of glutinous rice grains by comparing the alkali decomposition assessment to the gelatinization temperature of cooked starch, gel consistency, starch amylose content, and seed elongation ratio of the starch. Three replicates of four glutinous rice grains were randomly milled to obtain glutinous rice flour. Differentiation was observed both between and within highland glutinous rice varieties. Glutinous rice landraces can be classified into three groups: hard glutinous rice (KH5, PAKP5), medium-hard glutinous rice (KH2), and soft glutinous rice (PAKP4). The study also compared the characteristics of RD4 (hard glutinous rice) and RD6 (soft glutinous rice) glutinous rice varieties. The third part aimed to determine the differences in nucleotide sequences of genes related to the cooking quality of four glutinous rice populations obtained through random sampling from highland glutinous rice populations, along with two comparative glutinous rice varieties. DNA extraction was conducted for five samples per population, and PCR reactions were performed using specific primers for three cooking quality-related genes: SSIIa, ISA, and PUL genes. The partial nucleotide sequence differences of each gene were then analyzed. In this study, no differences in the partial nucleotide sequences of all studied genes were found among the glutinous rice landrace populations and the check varieties. In conclusion, the present study illustrates that the two glutinous rice landraces, consisting of four populations, maintained a low level of genetic diversity within each population. However, there were high levels of total genetic diversity between populations and genetic differentiation in crop morphology and cooking quality traits. The low level of genetic diversity within populations could be explain by the four glutinous rice landraces populations faced genetic drift due to founder effect during the kept from previous study for the second generation. Through the study of differences in nucleotide sequences, no nucleotide sequence differences were found among glutinous rice populations in the three genes associated to cooking quality. Nevertheless, further research is required to focus on more nucleotide sequences of the studied genes and additional genes, including the whole genome sequencing to serve as a database for selection and the breeding program forglutinous rice varieties in the future. This includes the study of other factors that can potentially affect the quality of rice grains as well.