Use of Canopy Temperature Measurements as a Screening Tool for Drought Tolerance in Spring Wheat

Remotely sensed infrared canopy temperatures provide an efficient method for rapid, non-destructive monitoring of whole-plant response to water stress. Field studies were conducted in 1992 and 1993 to evaluate the potential for using canopy temperatures to screen for drought tolerance in wheat. In both years, 12 spring wheat (Triticum aestivum L.) genotypes were grown under two irrigation levels (well-watered and moisture-stressed) imposed between tillering and anthesis with a line-source sprinkler irrigation system. Canopy temperature measurements were taken in well-watered and moisture-stressed plots between 1330 and 1430 h (MDT) on five clear days in 1992 and seven clear days in 1993 during the late vegetative and early reproductive growth periods following closure of the plant canopy. Genotypes exhibited differences in mean canopy temperatures across the two irrigation levels and two years. Klasic consistently had the highest canopy temperature under moisture-stressed conditions, while Bannock and Pondera had the lowest. Bannock, Yecora Rojo and Klasic had the warmest canopies under well-watered conditions, while Vandal, Amidon and Rick had the coolest. Plot-to-plot variation in canopy temperature under water stress conditions was evident for differences in grain yield. Significant correlations between canopy temperature and yield under moisture-stress conditions and drought susceptibility index values indicated the potential for screening wheat genotypes for drought response.     

A model describing the flowering of single plants, and the heritability of flowering traits of Dimorphotheca pluvialis

In the development of new crops such as Dimorphoteca pluvialis (L.) Moench, improvement of flowering synchronisation is an important breeding objective. The flowering of single plants of Dimorphotheca pluvialis could be described by a logistic curve obtained by the regression of cumulative number of open flowers on time. The curve is characterised by three parameters, corresponding with the total number of flowers produced by the plant, the rate of flowering development and the day at which peak bloom is reached. From these parameters two other characteristics were derived, i.e., onset of flowering and duration of flowering. The use of the flowering model for selection for improved flowering synchronisation is discussed. Heritabilities of flowering traits were estimated using parent-offspring regression and variance components analyses. Onset of flowering and date of peak bloom showed high (>0.69), and total number of flowers moderate to high (0.30–0.90) heritability values, indicating that for these traits considerable progress may be expected from mass selection, particularly in the early selection generations. Duration of flowering showed low to moderate values (0.25–0.45), and methods other than mass selection (e.g. family selection) should be considered. Determination of phenotypic and genetic correlations revealed only an additive genetic correlation between date of peak bloom and duration of flowering (r _A = 0.80 and 0.69 for 1993 and 1994, respectively), suggesting the possibility of indirect selection for curtailed duration of flowering by means of selection against late date of peak bloom. Duration of flowering, total number of flowers and onset of flowering were not correlated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Use of multiparental inbred populations to determine allelic relationships of molecular markers

The assessment of polymorphism exhibited by molecular markers is an arduous but essential task that facilitates the use of molecular tools by breeders and geneticists. For that purpose, the value of a wheat composite population was assessed for characterizing the diversity of restriction fragment length polymorphism (RFLP) markers developed by INRA-Génoblé. The polymorphism of 13 genomic probes was measured over a set of 80 inbred lines randomly extracted by single-seed descent from a composite-cross of 16 wheat lines. The 13 probéenzyme combinations revealed 27 loci with codominant polymorphism. As many bands were so far unmapped, the segregational analysis of the progenies appeared very suitable for complex patterns, both in determining allelic relationships and in revealing linkage between loci. Allelic diversity, band sizes and chromosomal location assessed from nullisomic-tetrasomic lines are given for the 27 loci.     

Correlated response to recurrent selection for groat-oil content in oats

Summary One hundred random oat (Avena sativa L.) lines from a base (C₀) and each of three populations (C₁, C₂, and C₃) improved for groat (caryopsis) oil content by phenotypic recurrent selection were evaluated for correlated changes in several unselected agronomic traits. In addition, the parents of the base population and four check varieties were evaluated for the same traits. Phenotypic recurrent selection for high groat-oil content resulted in no significant correlated response in mean expression of any trait. Mean grain yield, biomass, groat yield, and harvest index of the improved populations were equal or superior to the mean of the parents and, with the exception of harvest index, equivalent to the mean of the check varieties. Mean test weight and seed weight of all populations were lower than for parents or check varieties. Selection for high groat-oil content caused a decline in genotypic variance for test weight and groat fraction, but reductions in genotypic variance for heading date and plant height may have resulted from culling for good agronomic type. Broad-sense heritability remained moderate to high for all traits except groat fraction. Phenotypic and genotypic correlation coefficients revealed negative, though mostly nonsignificant, relationships between groat-oil content and several traits, which may reflect a purported bioenergetic limitation to increasing groat-oil content in oats. Oil yield, however, was positively correlated with grain and groat yield, groat fraction, biomass, and harvest index. Results suggest that development of high-oil oat cultivars with current levels of production traits via phenotypic recurrent selection is possible.Journal Paper no. J-13038 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011. Project 2447.     

Genetic parameters of several biochemical compounds from green coffee, Coffea canephora

A factorial crossing scheme of Cofflea canephora (two parents from the Congolese group crossed to 14 parents of the Guinean group) was used to evaluate genetic parameters of several biochemical compounds, bean weight and crop outturn (ration of dry bean weight 10 fresh berry weight). For most characters studied, additive genetic effects were preponderant. Narrow-sense heritability was high for caffeine content (h²_ns= 0.80), fat matter content (h²_ns, = 0.74), bean weight (h²_ns= 0.73) and crop outturn (h²_ns= 1). It was intermediate for trigonelline (h²_ns= 0.38) and chlorogenic acid (h²_ns= 0.36) content. Only sucrose content had a low narrow-sense heritability (h²_ns=0.11). There were few genetic and enviromnental correlations, Consequences for breeding, in relation to coffee drinking quality, are discussed.     

Effect of genome composition and cytoplasm on petal colour in resynthesized amphidiploids and sesquidiploids derived from crosses between Brassica rapa and Brassica oleracea

The effect of genome composition and cytoplasm on petal colour was studied in Brassica. Three accessions of yellow‐petalled B. rapa (2n= 20, AA) were crossed with a white‐petalled B. oleracea var. alboglabra (2n= 18, CC) and with three cream‐yellow‐petalled B. oleracea var. gongylodes (2n= 18, CC) to produce resynthesized B. napus (2n= 38, AACC or CCAA) and sesquidiploids (2n= 29, AAC or CAA). Petal colour was measured with a Hunter automatic colour difference meter. The results revealed that petal colour in Brassica is controlled by nuclear genes and by cytoplasmic factors. Additive and epistatic gene effects were involved in the action of nuclear genes. When crosses were made between yellow‐petalled B. rapa and white‐petalled B. oleracea var. alboglabra, significant additive, epistatic and cytoplasmic effects were found. White petal colour was partially epistatic over yellow petal colour. When crosses were made between yellow‐petalled B. rapa and cream‐yellow‐petalled B. oleracea var. gongylodes, only epistatic effects were detected. Yellow petal colour was epistatic over cream‐yellow.     

Use of component analysis in QTL mapping of complex crop traits: a case study on yield in barley

Genes contributing to the quantitative variation of a complex crop trait can be numerous. However, using existing approaches, the number of quantitative trait loci (QTL) detected for a trait is limited. Therefore, rather than looking for QTL for a complex trait itself, determining QTL for underlying component traits might give more information. In this study the potential of component analysis in QTL mapping of complex traits was examined using grain yield in spring barley as an example. Grain yield was divided into three components: number of spikes/m², number of kernels/spike, and 1000‐kernel weight. These traits were measured for individuals of a recombinant inbred‐line population in field trials conducted over 2 years. By the use of an approximate multiple QTL model, one to eight QTL were detected for each trait in a year. Some QTL were mapped to similar positions in both years. Almost all QTL for yield were found at the position of or in close proximity to QTL for its component traits. A number of QTL for component traits were not detected when yield itself was subjected to QTL analysis. However, relative to the QTL for yield itself, all component‐trait QTL did not explain the variation in yield better. The results in relation to the potential of using component analysis in studying complex crop traits are discussed.     

Mapping QTLs for Yield Stability in Durum Wheat Grown under Different Water Regimes

Among the most important Mediterranean annual crops, durum wheat is widely grown in drought-prone areas. Therefore, improving water-use efficiency （WUE） of durum wheat represents a major breeding goal. IDu-WUE （Improving Durum wheat for Water Use Efficiency and yield stability through physiological and molecular approaches） is a collaborative project among public and private research centres in Italy, Spain and WANA （West Asia and North Africa） countries （Morocco, Tunisia, Syria and Lebanon） funded by the European Union aimed at investigating the genetic variation for WUE and yield stability in durum wheat grown in Mediterranean droughtprone areas. During the first year of the project, a number of morpho-physiological traits （e.g. early vigour, flowering time, leaf rolling, number of fertile tillers, etc.）, WUE, WUE-related traits （e.g. carbon isotope discrimination, canopy temperature, chlorophyll fluorescence, etc.）, yield and its components have been investigated in a RIL population （249 lines） and a collection of ca. 190 durum wheat accessions characterized by a high level of linkage disequilibrium （Maccaferri et al., 2005）,     

TILLING and Ecotilling the Plant Kingdom

The modem crop scientist has a large amount of available nucleotide sequence information to identify genes of potential agronomic importance. Using reverse genetic approaches, specific genes can be disrupted, and hypotheses regarding gene function directly tested in vivo. Although a number of reverse genetic methods have been introduced, many are limited in application because they are organism-specific, expensive, transgenic, or only transiently disrupt gene function. However, traditional mutagenesis using chemical mutagens has been widely used as a forward genetics strategy to create many new crop plant varieties at relatively low cost. Mutagens such as ethyl methanesulphonate （EMS） cause stable point mutations and thus produce an allelic series of truncation and missense changes that can provide a range of phenotypes （Greene et al., 2003）. TILLING （targeting induced local lesions IN genomes） is a high-throughput reverse genetic strategy that combines traditional mutagenesis and SNP discovery methods （Colbert et al., 2001; McCallum et al., 2000）. To identify mutations, target regions of-l.5 kb are amplified with fluorescently labeled gene specific primers. Heteroduplexes are then formed between wild-type and mutant strands, mismatches are cleaved by incubation with a single-strand specific nuclease,     

Differentiation of the high molecular weight glutenin subunit D t x 2.1 of Aegilops tauschii indicated by partial sequences of its encoding gene and SSR markers

The devastating late blight pathogen Phytophthora infestans infects foliage as well as tubers of potato. To date, resistance breeding has often focused on foliage blight resistance, but tuber blight resistance is becoming more and more important in cultivated potatoes. In this study, a reliable tuber assay for resistance assessment was developed and foliage and tuber blight resistance (R) was compared in four mapping populations. In the RH4X-103 population, tuber blight resistance inherited independently from foliage blight resistance. Three specific R genes against P. infestans were segregating. The Rpi-abpt and R3a genes function as foliage-specific R genes, whereas the R1 gene acts on both foliage and tuber. In the segregating populations SHRH and RH94-076, tuber and foliage blight resistance correlated significantly, which suggests that resistance in foliage and tuber is conferred by the same gene (could be R3b) and quantitative trait loci (QTL), respectively. In the CE population neither tuber nor foliage resistance was observed.