Estimates of genetic variance and heterosis in F₁ winter x spring barley crosses (Hordeum vulgare, L.)

Four winter and four spring barley cultivars along with their F₁ hybrids were grown on the Hyslop Agronomy Farm near Corvallis, Oregon, a high rainfall site (over 1000 mm annually) located in the Willamette Valley. The experiment consisted of four replications. Ten seeds of each F₁ and parents were seeded in a three meter row. Plants were spaced 30 cm between and within the rows. Investigations were made to evaluate the presence of hybrid vigor when hybridizing winter and spring barley. Gene action estimates contributing to yield and its components were obtained. Additional information concerning the inheritance and the association of 12 agronomic traits and yield were also evaluated. The data were analyzed by using the factorial technique, analysis of variance, correlations, path-coefficient, parent-progeny regressions, and by polynomial and multiple regressions. The traits measured were: (1) total yield per plant, (2) kernel weight, (3) tiller number per plant, (4) kernel number per spike, (5) heading date, (6) plant height, (7) flag leaf area, (8) flag leaf width, (9) flag leaf length, (10) culm diameter, (11) head length, and (12) head extrusion. Heterobeltiosis was observed in all of the hybrids except in the cross between Adair and Short Wocus. The absence of hybrid vigor in this cross may be attributed to the fact that these two parents are closely related. Combining ability analysis as well as narrow sense heritability estimates indicated that additive gene action is more predominant in the expression of heading date, plant height, tiller number, head length, culm diameter, flag leaf width and kernel weight. Heterobeltiosis and high SCA estimates were observed in most of the hybrids for yield per plant and kernel number per spike. This implies that most of the genetic variation associated with these two traits resulted from non-additive gene action. The high SCA estimate observed for head extrusion indicates that this trait appeared to be controlled by non-additive gene action. Both additive and nonadditive gene action are important for the expression of flag leaf area and flag leaf length. When the 12 traits were correlated and the r values partitioned into direct and indirect effects it was observed that tiller number, kernel weight and kernel number per spike exerted the highest direct effect on yield. Plant height had a small positive direct effect, but an indirect effect on yield through kernel weight. It was further observed that a negative association exists between tiller number and kernel weight. This indicates that, in this barley population, it would be difficult to select for a plant containing large grain type and short stature, but it may be easy to select short plants with a relatively large number of tillers and high kernel number per spike. Path coefficient analysis indicated further that flag leaf area has a negative direct effect on yield and the remaining six traits have a negligible or no direct effect on yield, indicating that these traits can not be used as selection criteria. More genetic variability for tiller number and kernel number per spike was noted in the winter barley while more genetic variability for kernel weight was found in the spring barley. The results of this study suggest that increases in yield could be achieved by selecting plants with relatively high tiller number and high kernel weight. Selection for a high kernel number per spike can be accomplished by selecting for large culms and longer peduncle. By this procedure the breeder can take advantage of the additive genetic variance associated with tiller number and kernel weight and by the positive correlation that exists between culm size and peduncle length with kernel number per spike

New faba bean genotypes resistant to chocolate spot caused by «Botrytis fabae»

The response of sixty-seven genotypes of faba bean (Vicia faba) to the virulent isolate IBf24 of Botrytis fabae was studied under field conditions. Five of these genotypes (LPF39, LPF113, LPF44, LPF237 and LPF05) were moderately resistant to chocolate spot according to their MDI (mass disease index). Ten lines (LPF38, LPF41, LPF64, LPF95, LPF106, LPF132, LPF225, LPF228, LPF23, LPF233) were moderately susceptible, and fifteen lines (LPF54, LPF61, LPF66, LPF89, LPF124, LPF129, LPF131, LPF134, LPF138, LPF152, LPF173, LPF174, LPF190, LPF274, BPL710) susceptible as shown by their MDI values but with low AUDPC (area under disease progress curve) values and were believed to have an overall tolerance to the disease. Fourteen of the genotypes tested in the field, as well as the resistant BPL710 and the susceptible Rebaya 40 controls, were further screened under greenhouse conditions in order to confirm the field evaluation. In both the field and the greenhouse trials, the four lines LPF44, LPF237, LPF05 and LPF113 showed the highest level of resistance to the disease. These trials also revealed that genotypes with only overall tolerance may yet constitute interesting sources of resistance. Genotype BPL710, with known resistance to B. fabae races in the Mediterranean region, was found to be susceptible in the field but moderately susceptible in the greenhouse, suggesting the appearance of new races of this pathogen

Assessment of the genetic diversity of the Tunisian citrus rootstock germplasm

<p>Abstract</p> <p>Background</p> <p>Citrus represents a substantial income for farmers in the Mediterranean Basin. However, the Mediterranean citrus industry faces increasing biotic and abiotic constraints. Therefore the breeding and selection of new rootstocks are now of the utmost importance. In Tunisia, in addition to sour orange, the most widespread traditional rootstock of the Mediterranean area, other citrus rootstocks and well adapted to local environmental conditions, are traditionally used and should be important genetic resources for breeding. To characterize the diversity of Tunisian citrus rootstocks, two hundred and one local accessions belonging to four facultative apomictic species (<it>C. aurantium</it>, sour orange; <it>C. sinensis</it>, orange; <it>C. limon</it>, lemon; and <it>C. aurantifolia</it>, lime) were collected and genotyped using 20 nuclear SSR markers and four indel mitochondrial markers. Multi-locus genotypes (MLGs) were compared to references from French and Spanish collections.</p> <p>Results</p> <p>The differentiation of the four varietal groups was well-marked. The groups displayed a relatively high allelic diversity, primarily due to very high heterozygosity. Sixteen distinct MLGs were identified. Ten of these were noted in sour oranges. However, the majority of the analysed sour orange accessions corresponded with only two MLGs, differentiated by a single allele, likely due to a mutation. The most frequent MLG is shared with the reference sour oranges. No polymorphism was found within the sweet orange group. Two MLGs, differentiated by a single locus, were noted in lemon. The predominant MLG was shared with the reference lemons. Limes were represented by three genotypes. Two corresponded to the 'Mexican lime' and 'limonette de Marrakech' references. The MLG of 'Chiiri' lime was unique.</p> <p>Conclusions</p> <p>The Tunisian citrus rootstock genetic diversity is predominantly due to high heterozygosity and differentiation between the four varietal groups. The phenotypic diversity within the varietal groups has resulted from multiple introductions, somatic mutations and rare sexual recombination events. Finally, this diversity study enabled the identification of a core sample of accessions for further physiological and agronomical evaluations. These core accessions will be integrated into citrus rootstock breeding programs for the Mediterranean Basin.</p

Mapping novel QTLs for tolerance to salt stress at the late vegetative stage in durum wheat (Triticum durum L.)

Salt stress adversely affects the global durum wheat productivity. Breeding for salinity tolerance is an effective approach to improve crop production under saline conditions provided it is based on a good understanding of the genetic control of salinity tolerance. The present study was conducted, at the university of Tsukuba (in 2014), with the objective of mapping QTLs conferring salt tolerance in F2:3 populations of durum wheat derived from a cross between Razzek (salt sensitive variety) and Saragolla (salt tolerant variety). Two QTLs for salt tolerance were detected on chromosome 4B and 5B conferring the proportion of dead leaves with major effects. These two QTLs, which explained 68% of total phenotypic variation of %DL are an ideal candidate for Marker Assisted Selection (MAS) in wheat breeding programs and selection strategies to increase wheat production under saline conditions in order to meet the increasing global demand

Molecular diagnosis of Rickettsia infection in patients from Tunisia

International audienceDiagnosis of rickettsioses had largely benefited from the development of molecular techniques. Unfortunately, in Tunisia, despite the large number of rickettsia( cases registered every year, the Rickettsia species remain unidentified. In this study, we aimed to detect the Rickettsia species in clinical samples using molecular tests. A study was established to analyze skin biopsies, cutaneous swabs, and cerebrospinal fluid samples taken from clinically suspected patients to have rickettsial infection. Two molecular techniques were used to detect Rickettsia DNA: quantitative real time PCR (qPCR) and reverse line blot test (RLB). An analysis of the RLB hybridization assay results revealed the presence of Rickettsia DNA in skin biopsies (40.6%) and swabs (46.7%). Rickettsia conorii was the most prevalent identified species among tested samples. Other species of interest include Rickettsia typhi and Rickettsia massiliae. Using qPCR positivity rates in skin biopsies was 63.7% against 80% in swabs. R. conorii was the most frequently detected species, followed by R typhi. The agreement between the two techniques was 68.6% (kappa = 0.33). Molecular tests, especially using specific probes qPCR, allow for a rapid, better and confident diagnosis in clinical practice. They improve the survey of Mediterranean spotted fever which is considered to be the most important rickettsial infection in humans in Tunisia. (C) 2016 Elsevier GmbH. All rights reserved

Effects of sowing date on severity of blight caused by Ascochyta rabiei and yield components of five chickpea cultivars grown under two climatic conditions in Tunisia

Five chickpea cultivars, Chitoui, Neyer, Kasseb, Beja 1 and Bouchra, were planted on three sowing dates at two Experimental Stations in Tunisia: Bou Salem in the north and the more southerly Mornag, where the climate is drier. Severity of blight, caused by Ascochyta rabiei, was measured on a 1–9 scale (defined) on vegetative parts and on pods as percent infected and percent infected that were empty. At both locations, disease was essentially absent on plants sown on the third dates but present on plants sown on the two earlier dates. At Bou Salem, disease severity was highest for the second sowing date whereas at Mornag it was highest for the first sowing date; but for each sowing date, disease severity was lower at Mornag than at Bou Salem. Yield components were measured as number of pods per plant, number of seeds per plant, number of seeds per 100 pods, 100 seed weight and weight of seeds per plant. Both disease severity and yield differed significantly among sowing dates (differently at each location) and also among cultivars for each sowing date, these differences depending both on sowing date and location. A lower yield was always associated with a higher disease severity, although the quantitative relationship differed between cultivars and locations. Cultivar Beja 1 had the lowest vegetative disease scores at both locations and both sowing dates 1 and 2. Beja 1 also scored well for all yield components. Plants sown on the third (latest) date gave the highest yields for all cultivars at both locations (except for an unusually high yield of Neyer at Mornag on sowing date 2), in some instances being more than double those from the earlier sowing dates. Thus, in contrast to other studies, late sowing did not result in yield loss