No abstract

The use of combinations of two or more genes controlling carbohydrate characters of corn is an attractive way to improve table quality of sweet corn. Poor seed quality of the inbred lines hinders the progress of this strategy for hybrid seed production. The objective of this study was to evaluate sweet corn inbred lines with combinations of double and triple recessive genes for germination percentage, seed vigor, total sugar content, and starch content. Eleven sweet corn genotypes including seven inbred lines (F6 generation) with different combinations of genes controlling carbohydrate characters and four F1 hybrids were used. The germination experiment was conducted under standard test between papers (BP) and accelerated aging (AA) test. The data were recorded for germination percentage, germination speed, normal and abnormal seedling, seedling length, and seedling dry weight. The seeds were analyzed for total sugar and starch content in endosperm at maturity stage. The results showed that single recessive genotype (sh2sh2) had high germination percentage and seedling vigor. The combinations of bt or sh2 gene with wx gene resulted in low germination percentage and poor seedling vigor. However, combinations of triple recessive genes (btbt sh2sh2 wxwx) had good germination in BP test but they performed poorly in AA test.

Mechanization is required to increase labour productivity and improve grain quality for rainfed lowland rice in Lao PDR and neighbouring countries. An experiment was conducted in dry season in 2016 with three rice varieties and also in wet season in 2017 with two varieties to investigate the effect of introduction of combine harvester and flatbed dryer on milling quality of glutinous rice. The treatments were different harvest methods (hand and combine harvester), drying methods (sun and forced air drying with flatbed dryer) and storage period up to 6 months. Head rice yield (HRY) improved greatly with forced air drying with mean HRY of 46.1% compared to 28.8% in sun drying. Milling quality of grain harvested by combine was similar to that of handharvested crop. The results also revealed large difference in HRY between varieties; mean HRY across two seasons was 40.1% and 27.1% for Thadokkham (TDK8) and TDK11, respectively. These treatment effects and also their interactions on HRY were strongly related to the proportion of broken rice. HRY declined from 39.4% to 35.4% with 4-month storage, but there was no further reduction with 6-month storage. This study showed that the milling quality of glutinous rice improved greatly with the introduction of flatbed dryer but only little with combine harvester. Milling quality also varied greatly among varieties and slightly with storage period. Further study is required to investigate physiological and morphological characteristics of varieties and postharvest methods that determine the milling quality of rainfed lowland rice.

Studies aimed at determining gene function or identity are greatly facilitated by introgression lines and phenotyping tools. However, developing introgression lines can take six to eight generations to reach the desired level of background purity and homozygosity. The objective of this study was to use new generation genome-wide single nucleotide polymorphism (SNP) genotyping, along with a molecular marker for the alíele of interest, and a relevant phenotyping tool, to develop research populations with just four generations of backcrossing. Two populations were created for future research on aroma in rice {Oryza sativa L.): one derived from two indica parents and the other from one indica and one tropical japónica parent. The same recurrent parent was used for both populations. Single nuoleotide polymorphism genotyping of BC^Fg progeny selected previously on the basis of either a marker for fragrance or the presence of the fragrant compound and on the basis of morphological similarity to the recurrent parent showed that donor introgression ranged from <0.1% up to 35%. Single nucleotide polymorphism genotyping allowed the selection of a set of fragrant lines with minimal additional donor introgression after four generations. Metabolite profiling of the volatile blend in grains from parents and selected introgression lines showed that selected lines clustered with the recurrent parent. These new genotyping and phenotyping techniques enabled valuable genetic stocks to be developed in a short time for use In biochemical and genetic projects on fragrance in rice.

Upland rice usually gives poor germination under rainfed upland environement. To improve the seed germination, seed priming technique was assessed in this study. Seed of three upland rice (Oryza sativa L.) varieties (Leum Pua, ULR038 and Sakon Nakhon1, SKN) were primed with three different seed priming agents; distilled water, CaCl 2 and 300-fold diluted wood vinegar. Compared to untreated dry seeds, wood vinegar improved field emergence and improved drought tolerance of the rice seeds better than other priming agents, which 50 % for Leum Pua, 20 % for ULR038 and 16% for SKN, when watering was delayed for 7 days. All three priming agents increased the field emergence percentage by similar amounts when watering was delayed for 14 days. To understand how priming helped improvement of germination, antioxidation mechanism and sugar metabolism were examined. Level of malondialdehyde was markedly reduced in all three rice varieties in response to priming, which were associated with increased activity of antioxidant enzymes, guaiacol peroxidase and ascorbate peroxidase. Wood vinegar also accelerated amylase activity in ULR038 and SKN, but not the sugar content. The results suggest that wood vinegar is a potent priming agent for achieving rapid and uniform seed germination in upland rice.