Mapping of quantitative trait loci associated with chilling tolerance in maize (Zea mays L.) seedlings grown under field conditions

The effect of low growth temperature on morpho-physiological traits of maize was investigated by the means of a QTL analysis in a segregating F2:3 population grown under field conditions in Switzerland. Chlorophyll fluorescence parameters, leaf greenness, leaf area, shoot dry weight, and shoot nitrogen content were investigated at the seedling stage for two years. Maize was sown on two dates in each year; thus, plants sown early were exposed to low temperature, whereas those sown later developed under more favourable conditions. The main QTLs involved in the functioning of the photosynthetic apparatus at low temperature were stable across the cold environments and were also identified under controlled conditions with suboptimal temperature in a previous study. Based on the QTL analysis, relationships between chlorophyll fluorescence parameters and leaf greenness were moderate. This indicates that the extent and functioning of the photosynthetic machinery may be under different genetic control. The functioning of the photosynthetic apparatus in plants developed at low temperature in the field did not noticeably affect biomass accumulation; since there were no co-locations between QTLs for leaf area and shoot dry weight, biomass accumulation did not seem to be carbon-limited at the seedling stage under cool conditions in the fiel

QTL studies reveal little relevance of chilling-related seedling traits for yield in maize

Prolonged low temperature phases and short-term cold spells often occur in spring during the crucial stages of early maize (Zea mays L.) development. The effect of low temperature-induced growth retardation at the seedling stage on final yield is poorly studied. Therefore, the aim was to identify genomic regions associated with morpho-physiological traits at flowering and harvest stage and their relationship to previously identified quantitative trait loci (QTLs) for photosynthesis and morpho-physiological traits from the same plants at seedling stage. Flowering time, plant height and shoot biomass components at harvest were measured in a dent mapping population for cold tolerance studies, which was sown in the Swiss Midlands in early and late spring in two consecutive years. Early-sown plants exhibited chilling stress during seedling stage, whereas late-sown plants grew under favorable conditions. Significant QTLs, which were stable across environments, were found for plant height and for the time of flowering. The QTLs for flowering were frequently co-localized with QTLs for plant height or ear dry weight. The comparison with QTLs detected at seedling stage revealed only few common QTLs. A pleiotropic effect was found on chromosome 3 which revealed that a good photosynthetic performance of the seedling under warm conditions had a beneficial effect on plant height and partially on biomass at harvest. However, a high chilling tolerance of the seedling seemingly had an insignificant or small negative effect on the yiel

Quality protein introduced into waxy maize landraces of ethnic minorities

Ethnic minorities in South East Asia use waxy maize as a staple food, lacking in essential amino acids. Recently, we combined the recessive waxy and opaque2 alleles to double quality grains (w/o, pure amylopectin, high quality protein), which still must be introgressed into germplasm acceptable to ethnic minorities. Two w/o lines of Chinese and Thai background, respectively, were crossed once with two Vietnamese waxy landraces of good taste, WVN 3 and WVN 10. At the preferred harvest time for eating, dough stage, homozygous w/o F2 offspring with WVN 3 were equal in dehusked ear yield with commercial waxy hybrids and 40% superior in yield compared with WVN 10 F2 offsprings. In WVN 3 F2 crosses and F2 backcrosses with WVN 3, all w/o dehusked ears were equal in eat¬ing quality, grain protein content and a good leaf health; but the yield of dehusked ears and the grain tryptophan content was highest in the topcross. High quality germplasm is available now as a source of high quality protein for ethnic minorities. The two original w/o lines led to equal results in crosses with landraces, but their test hybrid was extremely high-yielding, indicating a good potential to breed for commercial high protein quality snacks in South East Asia

Cold Tolerance of the Photosynthetic Apparatus: Pleiotropic Relationship between Photosynthetic Performance and Specific Leaf Area of Maize Seedlings

The objective of this study was to elucidate the genetic relationship between the specific leaf area (SLA) and the photosynthetic performance of maize (Zea mays L.) as dependent on growth temperature. Three sets of genotypes: (i) 19 S5 inbred lines, divergently selected for high or low operating efficiency of photosystem II (ΦPSII) at low temperature, (ii) a population of 226 F2:3 families from the cross of ETH-DL3 × ETH-DH7, and (iii) a population of 168 F2:4 families from the cross of Lo964 × Lo1016 were tested at low (15/13°C day/night) or at optimal (25/22°C day/night) temperature. The latter cross was originally developed to study QTLs for root traits. At 15/13°C the groups of S5 inbred lines selected for high or low ΦPSII differed significantly for all the measured traits, while at optimal temperature the groups differed only with regard to leaf greenness (SPAD). At low temperature, the SLA of these inbred lines was negatively correlated with ΦPSII (r= − 0.56, p < 0.05) and SPAD (r = − 0.80, p < 0.001). This negative relationship was confirmed by mapping quantitative trait loci (QTL) in the two mapping populations. A co-location of three QTLs for SLA with QTLs for photosynthesis-related traits was detected in both populations at 15/13°C, while co-location was not detected at 25/22°C. The co-selection of SLA and ΦPSII in the inbred lines and the co-location of QTL for SLA, SPAD, and ΦPSII at 15/13°C in the QTL populations strongly supports pleiotropy. There was no evidence that selecting for high ΦPSII at low temperature leads to a constitutively altered SL

Genetic Diversity of Corn Hybrids from Different Sources in Thailand as Verified by Their Heterotic Pattern and Inbreeding Depression

ABSTRACT Growing a single cross or single crosses of genetically related inbreds in a large area has proved to be vulnerable to biological and physical hazards and lead to crop disaster when such genetic background became susceptible to ever changing environment. The purpose of this study was to measure genetic diversity of twelve commercial hybrids in Thailand. The genetic diversity was estimated by the formula : GD = 1 -[(H-C)/(H-S)], where GD, H, C and S stand for genetic diversity, average performance of the two hybrids, hybrid by hybrid cross, and average of the self-hybrids, respectively. The method assumes that heterosis is caused by cummulated effect of dominance and absence of epistasis. Theoretically, Two closely related hybrids with a GD of 0.25 should have one common inbred and other two inbreds are genetically related. Two hybrids with one inbred in common and the other two unrelated inbreds have the expected GD of 0.5. Two slightly related hybrids with a GD of 0.75 should have one related inbred and other two distinct inbreds. Two unrelated hybrids have an expected GD of 1.0. The estimation of genetic diversity of 12 commercial hybrids indicated that pairs of hybrids from the same company such as CP 999 x CP 888 (GD=0.25) and Pioneer 3013 x Pioneer 3012 (GD=0.26) each has closely related inbreds on both sides of the pedigree. Other three pairs of hybrids, Cargill 922 x Cargill 919 (GD=0.51), Pacific 700 x Pacific 328 (GD=0.57) and Uni. 98 x Uni-H 9728 (GD=0.67) each should have one inbred in common. The hybrids from different companies have GD in the range of 0.37-0.98 such as CP 999 x Cargill 919 (GD=0.37), SW 3853 x Pioneer 3013 (GD=0.75), Pacific 700 x Cargill 922 (GD=0.97), G5445A x Pioneer 3013 (GD=0.96), Uni-H 9728 x Cargill 919 (GD=0.96) and Cargill 922 x Uni. 98 (GD=0.98). The results showed that, the hybrids in Thai market still had considerable genetic diversity with noticeably exchanged of genetic background

Mapping of QTL affecting resistance against sorghum downy mildew (Peronosclerospora sorghi) in maize (Zea mays L)

Sorghum downy mildew (SDM) is one of the most destructive diseases of maize (Zea mays L) in South-East Asia. Understanding the genetic basis of downy mildew resistance (DMR) could increase the efficiency of breeding for disease resistant germplasm. The objectives of this study were to determine the number, genomic positions and genetic effects of quantitative trait loci (QTL) conferring resistance to SDM. The study included 251 F2:3 families derived from a cross between the two inbreds, Nei9008 (Thailand) and CML289 (CIMMYT), resistant and susceptible, respectively. Individuals in the population were genotyped for simple sequence repeat (SSR) and phenotypic resistance data were evaluated as percentage disease incidence in replicated field trials at three environments by Triple Lattice design. Heritability across environments was 94.3%. Traits were analyzed within and across environment using composite interval mapping. Nine QTLs were identified for resistance to SDM, one QTL each on chromosome 2, 3, 4, and 6, three QTLs on chromosome 5, and two QTLs on chromosome 9. Just one QTL on chromosome bin 5.07 came from the susceptible parent, all others from the resistant parent, Nei9008. The QTLs in chromosome bins 2.09 at umc1736, 5.03 at bnlg1902, and 6.01 at bnlg1867 had major effects and were consistent over all environments. A common map shows intriguing collocations of SDM QTLs with those for other disease and insect resistance QTLs from literature. As several consistent QTLs for downy mildew resistance are available now, an avenue is open for pyramiding multiple genes by marker assisted selection (MAS) that may control different mechanisms for resistance

Identification of metabolic and biomass QTL in Arabidopsis thaliana in a parallel analysis of RIL and IL populations

Plant growth and development are tightly linked to primary metabolism and are subject to natural variation. In order to obtain an insight into the genetic factors controlling biomass and primary metabolism and to determine their relationships, two Arabidopsis thaliana populations [429 recombinant inbred lines (RIL) and 97 introgression lines (IL), derived from accessions Col-0 and C24] were analyzed with respect to biomass and metabolic composition using a mass spectrometry-based metabolic profiling approach. Six and 157 quantitative trait loci (QTL) were identified for biomass and metabolic content, respectively. Two biomass QTL coincide with significantly more metabolic QTL (mQTL) than statistically expected, supporting the notion that the metabolic profile and biomass accumulation of a plant are linked. On the same basis, three out the six biomass QTL can be simulated purely on the basis of metabolic composition. QTL based on analysis of the introgression lines were in substantial agreement with the RIL-based results: five of six biomass QTL and 55% of the mQTL found in the RIL population were also found in the IL population at a significance level of P ≤ 0.05, with >80% agreement on the allele effects. Some of the differences could be attributed to epistatic interactions. Depending on the search conditions, metabolic pathway-derived candidate genes were found for 24–67% of all tested mQTL in the database AraCyc 3.5. This dataset thus provides a comprehensive basis for the detection of functionally relevant variation in known genes with metabolic function and for identification of genes with hitherto unknown roles in the control of metabolism

Combining three grain mutants for improved-quality sweet corn

Our goal was to improve sweet corn (Zea mays L.) by the novel approach of combining three grain mutants in one plant, shrunken-2 (sh2sh2), purple (Pr1Pr1C1C1), and opaque-2 (o2o2), for increased sugar, anthocyanin, and tryptophan content, respectively. We crossed purple opaque-2 waxy maize with sweet corn inbred lines. In the segregating selfed progenies, the opaque-2 gene was detected by the genetic marker phi057, the two other genes by the visual markers purple and shrunken. The purple opaque-2 sweet corn performed well in field tests; it had high total sugar content as required for sweet corn, improved protein quality indicated by 30% higher tryptophan content, and a 10-fold higher anthocyanin content than yellow kernel maize. This new sweet corn germplasm is a first step toward developing specialty maize with increased health benefits. © 2020 The Authors. Agricultural & Environmental Letters published by Wiley Periodicals, Inc. on behalf of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of Americ

ARPN Journal of Agricultural and Biological Science EFFECTS OF CHRONIC GAMMA IRRADIATION ON SHALLOT CHROMOSOMES (Allium ascalonicum Linn)

ABSTRACT Radiation contamination can occur from natural radiation or from man-made sources, such as radiation for medical research or for nuclear weapons manufacture. Radiation contamination can impact living things, the eco-system and the food chain, so several methods have been invented to test the level of radiation contamination. One of those methods is the Allium test, which is simple and cost-effective and makes it easy to clearly detect abnormalities from radiation. The objective of this study was to observe the effect of different levels of chronic gamma irradiation on the chromosomes of root tip cells of the shallot (Allium ascalonicum Linn.) (2n=16) and on growth of the shallots. Growing shallot bulbs were exposed to chronic gamma radiation from a Cobalt-60 source at the Nuclear Technology Research Center (NTRC), Kasetsart University, Thailand. They were placed 2 meters from the source and were exposed to 0, 10, 20, 30, 40, 50, 60, 70 and 80 Gy at the dose rate of 0.0078 Gy.min -1 . Following exposure, cells were fixed either immediately (0 hours) or after a 24-hour recovery period. Root tip squashes were observed by light microscope, 1,000 cells per specimen, to detect chromosome abnormalities. In the cells fixed 0 hours after exposure, chromosome abnormalities were observed in 1.967, 12.01, 0.964, 9.677, 9.417, and 8.923% of the cells of plants exposed to 10, 20, 30, 40, 50 and 60 Gy radiation, respectively, but no abnormalities were observed in the cells of plants exposed to 70 and 80 Gy. In the cells fixed 24 hours after exposure, chromosome abnormalities were observed in 4.216, 2.750, 14.955, 15.15 and 6.932% of the cells of plants exposed to 10, 20, 30, 40, and 50 Gy, respectively but no abnormalities were observed in the cells of plants exposed to 60, 70 or 80 Gy. That means root tip cells of the shallot can use for testing the low dose level of radiation contamination (10-60 Gy). The most commonly observed chromosome abnormality was micronucleus at interphase, followed by fragments and bridges. As for the growth rate following chronic irradiation, the height (leaf length) was recorded after 7 days and it was found that there was no significant different in growth rate among the treatment groups exposed to different doses of gamma irradiation, but the mean height of all the irradiated plants (2-5 cm) was significantly lower than that of the non-irradiated control plants (13 cm)