Relative Total Dry Weight Research Articles

Evaluation of Mung Bean Accessions for Salt Tolerance Based on Germination and Seedling Traits

Ten mung bean accessions collected from Bangladesh Agricultural Research Institute were exposed to two salinity levels (control and 8 dS m−1) to observe the sensitivity of their germination and early seedling traits. The observations were recorded on germination percentage, rate of germination, coefficient of germination, shoot length, root length and seedling dry weight. The accessions, salinity levels and their interaction exhibited significant differences for all the traits. The mean performance of all the traits reduced under salt stress as compared to control. Salt tolerant accessions showed less reduction in their germination and seedling traits under salinity than the other accessions tested. Considering salt tolerance index (STI) based on seedling dry weight, the order of tolerance was BD- 6882 > BD-10022 > BD-10024 > BD-10026 > BD-10023 > BD-10027 > BD-6885 > BD-6887 > BD- 6884 > BD-6875. Based on relative total dry weight (RTDW), three accessions viz. BD-6882, BD- 10022 and BD-10024 were identified as salt tolerant and other seven as moderately salt tolerant. The identified salt tolerant accessions could be a useful stock for further breeding programs to develop salt tolerant mung bean genotype of considerable economic value. Bangladesh Agron. J. 2024, 26(2): 16-26

Identification of Sri Lankan rice varieties having osmotic and ionic stress tolerance during the first phase of salinity stress

Salt tolerance of plants during the first phase of salt stress requires a combination of physiological traits conferring tolerance to both osmotic stress and ionic stress. Accordingly, the objectives of the present study were: (a) to screen a substantial number of varieties (102) from the Sri Lankan rice ( Oryza sativa ) germplasm and thereby identify varieties with osmotic and ionic tolerance during Phase I of salt stress development; and (b) to identify the physiological mechanisms that are responsible for osmotic and ionic tolerance. The 102 varieties tested included 51 traditional, 4 old-improved and 47 new-improved varieties, which were screened in nutrient solutions at 100 mM NaCl. Whole plant salt tolerance was quantified using relative leaf area (RL) and relative total dry weight (RW), i.e. leaf area and total dry weight at 100 mM Na+ as ratios of their respective values at 1 mM Na+, the unstressed control. Cluster analysis based on RL and RW enabled classification of Phase I salt tolerance of the screened varieties into five groups as, ‘highly tolerant’ (6 varieties), ‘tolerant’ (25), ‘moderately tolerant’ (32), ‘susceptible’ (30) and ‘highly susceptible’ (9). Capacity to maintain relatively high tissue water content, capacity for Na+ exclusion at the root surface and root xylem and tissue tolerance to excess shoot Na+ were identified as tolerance mechanisms of rice for salinity at Phase I. High shoot tolerance to Na+ contributed to tolerance in 40 out of the 63 varieties identified as Phase I-tolerant to varying degrees. In comparison, high or medium capacity to maintain either whole plant or shoot relative water content contributed to tolerance in 48 varieties, while Na+ exclusion at either of the two control points contributed to tolerance in 33 varieties. Based on the varietal phenotyping of the present study, suitable varieties can be selected: (a) for direct recommendation to areas of mild to transient salinity; (b) as parents in conventional breeding programmes to develop salt tolerant rice varieties; (c) for molecular biological studies to identify genes responsible for Phase I salt tolerance. DOI: http://dx.doi.org/10.4038/jnsfsr.v40i3.4699 J.Natn.Sci.Foundation Sri Lanka 2012 40 (3):251-280

Identification of quantitative trait loci associated with salt tolerance at seedling stage from Oryza rufipogon

Soil salinity is one of the major abiotic stresses affecting plant growth and crop production. In the present study, salt tolerance at rice seedling stage was evaluated using 87 introgression lines (ILs), which were derived from a cross between an elite indica cultivar Teqing and an accession of common wild rice (Oryza rufipogon Griff.). Substantial variation was observed for four traits including salt tolerance score (STS), relative root dry weight (RRW), relative shoot dry weight (RSW) and relative total dry weight (RTW). STS was significantly positively correlated with all other three traits. A total of 15 putative quantitative trait loci (QTLs) associated with these four traits were detected using single-point analysis, which were located on chromosomes 1, 2, 3, 6, 7, 9 and 10 with 8%-26% explaining the phenotypic variance. The O. rufipogon-derived alleles at 13 QTLs (86.7%) could improve the salt tolerance in the Teqing background. Four QTL clusters affecting RRW, RSW and RTW were found on chromosomes 6, 7, 9 and 10, respectively. Among these four QTL clusters, a major cluster including three QTLs (qRRW10, qRSW10 and qRTW10) was found near the maker RM271 on the long arm of chromosome 10, and the O. rufipogon-derived alleles at these three loci increased RRW, RSW and RTW with additive effects of 22.7%, 17.3% and 18.5%, respectively, while the phenotypic variance explained by these three individual QTLs for the three traits varied from 19% to 26%. In addition, several salt tolerant ILs were selected and could be used for identifying and utilizing favorable salt tolerant genes from common wild rice and used in the salt tolerant rice breeding program.

Assessment of genetic divergence in salt tolerance of soybean (Glycine max L.) genotypes

A large number of soybean (Glycine max L.) genotypes of diverse growth habit and adaptive characters were used in the experiment. Soil salinity-induced changes in nine morpho-physiological characters of 30-day-old seedlings of 170 soybean genotypes were compared in the study. The first and second principal components (PC) of principal component analysis (PCA) results accounted for 97 and 2.5%, respectively, of the total variations of soybean genotypes. The variation for the first PC was composed mainly of relative total dry weight (DW), relative shoot dry weight, as well as petiole dry weight. There were four clusters distinguished in the cluster analysis. The genotypes in cluster IV performed better in respect to relative total dry weight and relative shoot dry weight and hence having salt tolerance. The genotypes clusters III performed very poorly and those of clusters II and I were moderate to poor. D2 analysis indicated that the clusters differed significantly from each other. Discriminant function analysis (DFA) again asserts strongly that more than 92% of the genotypes were correctly assigned to clusters. Both PCA and DFA confirmed that the relative total DW followed by shoot and petiole DW were the major discriminatory variables, and the root DW were the secondary important variables to distinguish genotypes into groups. In this study, multivariate analyses were used in identifying the soybean genotypes of desirable traits for salt tolerance.

DIFFERENTIAL RESPONSE OF RICE PLANTS TO LOW-PHOSPHORUS STRESS AND ITS PHYSIOLOGICAL ADAPTIVE MECHANISM

ABSTRACT Two rice genotypes, JX17 (Oryza sativa ssp. japonica) and ZYQ8 (Oryza sativa ssp. indica), which had been the parents of the 127-line double haploid (DH) population for construction of molecular linkage map, were chosen to study their response to low phosphorus (P) stress. The results indicated that JX17 had advantages over ZYQ8 on some traits associated with phosphorus uptake efficiency, such as root dry weight, root-exuded acid phosphatase activity, root-exuded organic acids and proton. Consequently, JX17 had higher relative total dry weight and was regarded as the non-sensitive genotype to low phosphorus stress. Physiological response of the two genotypes to P deficiency was studied in monoculture and in mixed culture. The results showed that, compared with monoculture, JX17 absorbed more P and had higher biomass in mixed culture condition under P stress. ZYQ8, by contrast, suffered from P stress to a much greater extent, with lower P uptake and biomass. JX17 had a higher P uptake rate expressed as P amount per root length which is suggested to be the main reason for its insensitivity to low P stress.

DETECTION AND VERIFICATION OF QUANTITATIVE TRAIT LOCI AFFECTING TOLERANCE TO LOW PHOSPHORUS IN RICE

Phosphorus (P)-deficiency in rice (Oryza sativa L.) may cause yields reductions. This research was conducted to map quantitative trait loci (QTL) for tolerance to low-P stress in a double-haploid (DH) line, and to verify these loci in another SSD9 population, which is the ninth generation of single-seed-distribution population derived from the same parents. Two populations were cultured solution at different period. By using the linkage map, QTLs for traits associated with tolerance to low-P stress were located. Results indicated that for DH population, one restricted fragment length polymorphism (RFLP) marker located on chromosome 6 was closely associated with relative root dry weight, relative shoot dry weight, and relative total dry weight. Two QTLs affected relative P uptake content. One micro-effect QTL was found to be associated with relative P utilization efficiency. For relative amounts of root exuded acid phosphatase, relative P allocation between shoot and root, relative plant P concentration, and relative shoot P concentration, one micro-effect QTL was detected for each one. Quantitative trait loci for 3 traits were detected for both DH and SSD9 populations, but the loci for each located trait were inconsistent between two populations; the reason for inconsistency in QTLs was analyzed. The main reason could be the difference in solution environment.

Taro Responses to Excess Copper in Solution Culture

Cupric sulfate pentahydrate (CuSO4·5H2O) has been proposed for use in Hawaii as a molluscicide to control golden apple snail (Pomacea canaliculata Lamarck) infestations of taro [Colocasia esculenta (L.) Schott]. Two hydroponic, greenhouse studies were conducted to determine the effects of solution Cu2+ levels on taro growth, the solution Cu2+ toxicity threshold, and useful diagnostic indicators of Cu toxicity. In the first experiment, taro cultivars Lehua maoli and Pololu were grown at nine levels of Cu2+ ranging from 0.5 to 25.0 μm. In the second experiment, `Lehua maoli' was grown at six levels of Cu2+ ranging from 0.25 to 2.5 μm. Significant (P ≤ 0.05) toxic effects included reduced dry matter production, leaf area, and root length: root dry weight ratio, and both impaired photosynthesis and a generalized reduction of cation accumulation in leaf blade tissue. The solution Cu2+ toxicity threshold (based on 90% of relative total dry weight) for young taro plants was 1.2 μm. Because Cu does not accumulate in leaf blade tissues with increasing solution Cu2+ levels, leaf Cu concentration cannot be used as a diagnostic indicator of Cu toxicity in taro.

Identification of quantitative trait loci affecting tolerance to low phosphorus in rice (Oryza Sativa L.)

Phosphorus (P)-deficiency in rice (Oryza. Sativa. L) may cause yield reductions. This research has been conducted to map quantitative trait loci (QTLs) for tolerance to low phosphorus stress in a doubled haploid (DH) population. By using the linkage map of this population, the QTLs for relative dry weight, relative P content and relative P utilization efficiency have been located. The results indicate that one RFLP marker located on chromosome 6 is closely associated with relative root dry weight, relative shoot dry weight and relative total dry weight, which explain 24.9%, 20.5% and 25.2% of the total phenotypic variations, respectively. Two QTLs affect relative P uptake content, which account for 20.7% of the total phenotypic variations. One micro-effect QTL has been found to be associated with relative P utilization efficiency. It is suggested that the P uptake efficiency is more associated with P efficiency. Among the secondary physiological indices of P uptake efficiency, the root dry weight is more important than others.