The genetic basis of cold-tolerance was investigated by analyzing the quantitative trait loci (QTL) of an F2:3 population derived from a cross between two lines bred for contrasting cold-tolerance using chlorophyll fluorescence as a selection tool. Chlorophyll fluorescence parameters, CO2 exchange rate, leaf greenness, shoot dry matter and shoot nitrogen content were determined in plants grown under controlled conditions at 25/22 degrees C or 15/13 degrees C (day/night). The analysis revealed the presence of 18 and 19 QTLs (LOD > 3.5) significantly involved in the variation of nine target traits in plants grown at 25/22 degrees C and 15/13 degrees C, respectively. Only four QTLs were clearly identified in both temperatures regimes for the same traits, demonstrating that the genetic control of the performance of the photosynthetic apparatus differed, depending on the temperature regime. A major QTL for the cold-tolerance of photosynthesis was identified on chromosome 6. This QTL alone explained 37.4 of the phenotypic variance in the chronic photoinhibition at low temperature and was significantly involved in the expression of six other traits, including the rate of carbon fixation and shoot dry matter accumulation, indicating that the tolerance to photoinhibition is a key factor in the tolerance of maize to low growth temperature. An additional QTL on chromosomes 2 corresponded to a QTL identified previously in another population, suggesting some common genetic basis of the cold-tolerance of photosynthesis in different maize germplasms.

The effect of low growth temperature on morpho-physiological traits of maize was investigated by the means of a QTL analysis in a segregating F(2:3) 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 field.

This work was conducted to identify mungbean genotypes showing yield stability and resistance to mungbean yellow mosaic virus (MYMV) disease. Sixteen genotypes were evaluated in a randomized complete block design with two replications for two years (2011 and 2012) at three locations (Gazipur, Ishurdi and Madaripur) of the Bangladesh Agricultural Research Institute. An analysis of variance exhibited significant effects of genotype (G), environment (E), and genotype × environment (G×E) on grain yield. Among eight agronomic characters, the principal component 1 (PC1) was always higher than the PC2. Considering G×E interaction, BM6 was the best genotype at all three locations in both years. Based on grain yield and stability performance, BM6 ranked first while the worst performing genotypes were BM1 and G10. Based on discrimination and representation, Gazipur was identified as an ideal environment for these mungbeans. Relationship between soil-plant analysis developments (SPAD) value was positive with yield but negative with MYMV severity. BM6, G1 and G2 were considered as promising sources of resistance for low disease score and stable response across the environments. The environment proved to have an influence on MYMV infection under natural infestation. A positive correlation was observed between disease score and the temperature under natural growing condition.

Prolonged low temperature phases and shortterm cold spells often occur in spring during the crucial stages of early maize (Zea mays L.) development. The eVect of low temperature-induced growth retardation at the seedling stage on Wnal yield is poorly studied. Therefore, the aim was to identify genomic regions associated with morpho-physiological traits at Xowering and harvest stage and their relationship to previously identiWed 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. SigniWcant QTLs, which were stable across environments, were found for plant height and for the time of Xowering. The QTLs for Xowering 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 eVect was found on chromosome 3 which revealed that a good photosynthetic performance of the seedling under warm conditions had a beneWcial eVect on plant height and partially on biomass at harvest. However, a high chilling tolerance of the seedling seemingly had an insigniWcant or small negative eVect on the yield.

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 S 5 inbred lines, divergently selected for high or low operating efficiency of photosystem II (U PSII ) at low temperature, (ii) a population of 226 F 2:3 families from the cross of ETH-DL3 · ETH-DH7, and (iii) a population of 168 F 2:4 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 S 5 inbred lines selected for high or low U PSII 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 U PSII (r = À 0.56, p < 0.05) and SPAD (r = À 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 U PSII in the inbred lines and the co-location of QTL for SLA, SPAD, and U PSII at 15/13°C in the QTL populations strongly supports pleiotropy. There was no evidence that selecting for high U PSII at low temperature leads to a constitutively altered SLA.Abbreviations: CER -carbon exchange rate; U PSII -operating efficiency of photosystem II; PPFDphotosynthetic photon flux density; QTL -quantitative trait locus; SLA -specific leaf area; SPAD -soil plant analysis development, leaf greenness Molecular Breeding (2005) 16: 321-331 Ó Springer 2005