Jirawat Sanitchon

Evaluation of salt tolerance at the seedling stage in rice genotypes by growth performance, ion accumulation, proline and chlorophyll content

AimsThe objectives of this study were to evaluate salt tolerance level of rice genotypes using the well-established screening criteria; the salt injury score, survival percentage and ratio between Na+ and K+, as well as the contents of proline and chlorophyll, and to identify the relationship between salt tolerance and physiological characters.MethodsOne hundred and six rice genotypes were grown in hydroponic solutions subjected to salt stress and evaluated for salt tolerance ability and the physiological parameters. Multivariate cluster analysis was performed based on salinity tolerance scores (ST scores; score 1 being the most tolerant, score 9 the most sensitive), survival percentage and Na+/K+ ratio.ResultsST scores based on salt injury symptoms were negatively correlated with survival percentage and chlorophyll concentration in the stressed seedlings but positively correlated with Na+/K+ ratio and proline content. Rice genotypes were classified into five salt tolerance groups: tolerant (T), moderately tolerant (MT), moderately sensitive (MS), sensitive (S) and highly sensitive (HS). The means of ST scores were significantly different among the five tolerance groups indicating that the ST score was the most reliable index for identifying salt tolerance. The means of Na+/K+ ratio and proline content in stressed seedlings were distinctively different between the extreme T and HS groups, but the means among the intermediate groups (MT, MS and S) were not significantly different. Chlorophyll content, on the other hand, was not related to the levels of salt tolerance.ConclusionsIn addition to the commonly used Na+/K+ ratio, proline content is suggested to be another useful criterion to differentiate salt-tolerant from salt-sensitive rice. This study also identified several Thai improved and local cultivars with the level of salt tolerance and physiological characters comparable to Pokkali, the standard salt-tolerant donor and may be utilized as alternative sources of salt tolerance alleles.

Physiological and biochemical parameters for evaluation and clustering of rice cultivars differing in salt tolerance at seedling stage

Salinity tolerance levels and physiological changes were evaluated for twelve rice cultivars, including four white rice and eight black glutinous rice cultivars, during their seedling stage in response to salinity stress at 100 mM NaCl. All the rice cultivars evaluated showed an apparent decrease in growth characteristics and chlorophyll accumulation under salinity stress. By contrast an increase in proline, hydrogen peroxide, peroxidase (POX) activity and anthocyanins were observed for all cultivars. The K+/Na+ ratios evaluated for all rice cultivars were noted to be highly correlated with the salinity scores thus indicating that the K+/Na+ ratio serves as a reliable indicator of salt stress tolerance in rice. Principal component analysis (PCA) based on physiological salt tolerance indexes could clearly distinguish rice cultivars into 4 salt tolerance clusters. Noteworthy, in comparison to the salt-sensitive ones, rice cultivars that possessed higher degrees of salt tolerance displayed more enhanced activity of catalase (CAT), a smaller increase in anthocyanin, hydrogen peroxide and proline content but a smaller drop in the K+/Na+ ratio and chlorophyll accumulation.

Pyramiding of blast and bacterial leaf blight resistance genes into rice cultivar RD6 using marker assisted selection

Blast caused by the fungus Magnaporthe oryzae (Hebert) Barr. and bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) are two major diseases of rice (Oryza sativa). The use of varietal resistance is the most appropriate strategy for controlling the diseases, and molecular assisted selection can potentially accelerate breeding programs. The objective of this study was to pyramid genes conferring resistance to blast and bacterial leaf blight diseases to rice cultivar RD6, using molecular assisted selection. Near-isogenic lines (NIL) derived from two blast resistant crosses (RD6 × P0489 and RD6 × Jao Hom Nin) were pyramided with IR62266 (xa5), to transfer bacterial leaf blight resistance to RD6 introgression lines. Five flanking sets of simple sequence repeat (SSR) markers (RM319/RM212, RM48/RM207, RM224/RM144, RM313/RM277 and RM122/RM159: four for blast and one for BLB resistance) were used for screening of introgression lines carrying five quantitative trait loci (QTLs) from the BC1F2 generation through to BC2F2:3 generation, and 12 pyramiding lines were identified. Gene validation for blast and bacterial leaf blight diseases was accomplished using artificial inoculation under greenhouse conditions. BC2F2:3 2-8-2-24 and BC2F2:3 2-8-2-25 showed greater levels of blast broad spectrum resistance (BSR) whereas BC2F2:3 2-8-2-36 expressed the highest of bacterial leaf blight resistance with a high blast BSR. Keywords: Gene pyramiding, introgression lines, molecular marker, Near-isogenic lines, SSR. African Journal of Biotechnology Vol. 12(28), pp. 4432-4438

Effects of Salt Stress after Late Booting Stage on Yield and Antioxidant Capacity in Pigmented Rice Grains and Alleviation of the Salt-Induced Yield Reduction by Exogenous Spermidine

Abstract Pigmented rice is receiving much attention due to the large amounts of bioactive compounds and various health benefits.However, little information is available on its agronomic and physiological aspects. This research aimed to explore the effects of salinity on yield and grain quality of pigmented rice and the modulation of salinity responses by exogenous application of spermidine (Spd). Four cultivars of rice were grown in pots until the early booting stage. Thereafter, the plants were sprayed with 1 mM Spd for 7 successive days before being irrigated with 25 mM NaCl instead of tap water until maturity. Grain yield, yield components and harvest index in all rice cultivars were negatively affected by this salinity stress. Pretreatment with Spd dramatically improved yield and yield components of salt-treated plants, particularly the salt-sensitive cultivar. The major yield components which were improved and contributed most to the dramatic increase in seed yield were the number of filled grains per panicle and panicle fertility. Moreover, Spd pretreatment resulted in an increase in K+/Na+ ratio in rice grains. Salt stress increased nutritional quality of mature grains, i.e., total phenolic content, anthocyanins, proanthocyanins and antioxidant activities (evaluated by FRAP, DPPH and ABTS assays) in all rice cultivars. Furthermore, all aspects of health-promoting nutritional characters were further enhanced by Spd pretreatment. Thus foliar spraying of Spd to rice plants prior to salt application improved grain yield as well as nutritional quality of colored rice grains in relation to total phenolics, flavonoid pigments and antioxidant capacities.

A modified ferrous oxidation-xylenol orange assay for lipoxygenase activity in rice grains.

Ferrous oxidation-xylenol orange assay reagent was reformulated by using spectral analysis of ferric-xylenol orange complex to detect low concentrations of lipoxygenase rice grain products. Reducing the levels of ferrous sulphate and xylenol orange in the FOX reagent enabled the detection of low concentrations of hydroperoxy fatty acid derived from lipoxygenase activity in the range of 0.1-1.5 μM. Protein, substrate and time courses of the modified FOX assay were studied to determine lipoxygenase activity in rice grain. The assay was also applicable as a high throughput technique for comparisons of lipoxygenase activity from various rice varieties. This has important implications for rapid screening for low-lipoxygenase containing rice cultivars in rice breeding program and grain quality during storage.

Pyramiding of four blast resistance QTLs into Thai rice cultivar RD6 through marker-assisted selection

Suwannual T., Chankaew S., Monkham T., Saksirirat W., Sanitchon J. (2017): Pyramiding of four blast resistance QTLs into Thai rice cultivar RD6 through marker-assisted selection. Czech J. Genet. Plant Breed., 53: 1–8. Thai rice cultivar RD6 is well known for its cooking and eating qualities. However it is susceptible to blast disease, a major rice disease caused by the fungus Magnaporthe oryzae. This study focused on the pyramiding of four QTLs for blast resistance located on chromosomes 1, 2, 11 and 12, from two RD6 introgression lines. Marker-assisted selection was performed and facilitated the selection with 8 microsatellite flanking markers to enable the selection in BC2F2:3 lines. All possible combinations of the four QTL alleles were assessed for blast resistance by artificial inoculation using 8 diverse isolates in a greenhouse and under field conditions using the upland short row method. The results showed that the RD6 introgression lines carrying a high number of QTLs for blast resitance achieved from pyramiding have high levels of blast resistance and broad spectrum of resistance to the blast pathogens prevalent in the region. Only one of the M. oryzae isolates, THL185, was virulent to all the breeding lines, suggesting that the identification of new blast resistance genes or QTLs and pyramiding them into RD6 for durable blast resistance and no yield penalty should be the focus of further research.

New sources of rice blast resistance obtained from Thai indigenous upland rice germplasm

Upland rice production plays an important role in both household consumption and crop rotation. Until now, a blast resistant upland variety has not been released in Thailand. The bimodal pattern of rain distribution in Thailand’s upland rice production areas create a favorable environment for the outbreak of leaf blast when seedling-tillering, and neck blast within the heading stage. The use of genetically resistant cultivars has proven to be an effective way to cope with this problem. In this study, 256 indigenous upland rice plants were screened for blast resistance under greenhouse and field conditions. Ten indigenous upland rice varieties, ULR292, ULR242, ULR219, ULR162, ULR161, ULR134, ULR109, ULR098, ULR081, and ULR066, were identified as resistant to leaf blast disease in both natural infection and artificial inoculation, under greenhouse conditions. Additionally, six of the ten varieties, ULR162, ULR161, ULR134, ULR109, ULR098, and ULR081, were found to be resistant to neck blast under field conditions. These new sources of blast resistance identified from indigenous upland rice varieties proved more resistant than the check varieties, depicting their potential for further use in Thailand’s rice blast resistance improvement program.

Application of LW7 marker for identification of progenies with male sterility gene in sweet sorghum population

Verificou-se o uso do marcador LW7 para identificacao de linhas mantenedoras B e restauradoras R em sorgo granifero e doce e para identificacao de linhas mantenedoras B nas geracoes F2, RC1F2 e RC2F2. Vinte e cinco acessos de sorgo foram avaliados e o marcador LW7 identificou corretamente aqueles que possuem o gene de macho-esterilidade (rf4) como Suphan Buril e 03B, os quais nao mostraram a banda de 779 pb. O cruzamento entre Suphan Buri1 e uma linha macho-esteril (A) 03A resultou macho-esteril, confirmando a utilidade do marcador em programas de melhoramento. Linhas B em geracoes F2, RC1F2 e RC2F2 foram identificadas pelo marcador LW7 e a taxa de segregacao de 3:1 para fertilidade e macho-esterilidade nas progenies das tres geracoes apoiaram o modelo de segregacao Mendeliana de um gene. O uso da selecao assistida por marcador foi bem sucedido para o desenvolvimento de linhas de sorgo sacarino com macho-estereis.