Genetic variation,genotype × environment interaction,and selection for tipburn resistance in lettuce in multi-environments

Tipburn is a calcium related and environmentally induced physiological disorder causing economic damage in all lettuce (Lactuca sativa L.) production regions. The objectives of this research were to determine (1) the genetic variation for tipburn incidence, (2) the genotype (G) × environment (E) interaction (GE) for tipburn incidence, and (3) the efficiency of field selection for tipburn resistance. Tipburn incidence was recorded over 2 years in Salinas, CA, and Yuma, AZ, for 55 romaine, crisphead, green leaf, and red leaf type cultivars, and over 3 years in Quebec for 15 romaine cultivars. Analysis revealed that G, E, and GE affected tipburn incidence, including crossover interactions that were not repeatable over years. This indicates that cultivar/breeding line evaluations should be based on mean performance and stability over multiple environments. Among lettuce types, only crisphead had significant genetic variability for tipburn resistance, reflecting the greater breeding effort applied to this type compared romaine, green and red leaf types. Analysis of a dataset with five romaine cultivars in eight environments in California, Arizona, and Quebec for 2 years revealed that Yuma in 2006 and Saint-Blaise in 2005 were highly correlated (r = 0.923, P < 0.05), and were the most discriminating and most representative environments for tipburn evaluation. Single plant selection for tipburn resistance in three F₂ romaine populations was ineffective. Further, the degree of head closure was significantly associated with tipburn incidence. Identification and selection of morphological characters associated with resistance in conjunction with direct selection against tipburn may be an effective method for genetic improvement of tipburn resistance.     

Occurrence of 2,3-dihydrofarnesoic acid, a spidermite repellent, in trichome secretions of Lycopersicon esculentum × L. hirsutum hybrids

The sesquiterpenoid spidermite repellent, 2,3-dihydrofarnesoic acid, occurs in trichome secretions of LA1363, an accession of the wild tomato Lycopersicon hirsutum. To better understand the inheritance of this sesquiterpene acid and its relationship with the quantity trichome secretions, interspecific crosses were made with five inbred lines of L. esculentum. Limited seed set and frequent seedling mortality led to small populations for each generation. Concentrations of residues in leaflet washes, comprised of trichome secretions and concentrations of 2,3-dihydrofarnsoic acids were determined in F1, F2 and backcross generations. Low concentrations of this acid occurred in F1 hybrids, suggesting there was dominance for low levels of the acid. However, concentrations of 2,3-dihydrofarnesoic acid were below minimum levels of detection in two backcross generations and in one of two F2 generations. Concentrations of leaflet wash residues were high on the L. hirsutum parent and low on the L. esculentum parents. Concentrations on hybrids were generally intermediate. However, high residue concentrations were present on a few F1 and F2 hybrids, Residue and 2,3-dihydrofarnesoic acid concentrations were not correlated in F1 or in backcross generations and were uncorrelated in one of two F2 generations. In the F2 obtained by sib-mating, residue concentrations were correlated with 2,3-dihydrofarnesoic acid concentrations. Although small population sizes and perhaps other factors did not allow delineation of genetic control of the presence or abundance of 2,3-dihydrofarnesoic acid, interspecific hybrids that produce 2,3-dihydrofarnesoic acid provide the experimental plants essential for research designed to provide a better understanding of the role of 2,3-dihydrofarnesoic acid in host-plant resistance of tomato to mites and insects.     

Generation and characterisation of colchicine-induced polyploid Lavandula × intermedia

Double podding in cultivated chickpeas (Cicer arietinum L.) can increase yield and yield stability. In the present study, we performed reciprocal crosses of ‘kabuli’ (double podded) and ‘desi’ (single podded) chickpeas to determine (i) the expressivity and penetrance of double podding, (ii) the correlations of yield and yield components, and (iii) the heritability of double podding, flower color, and stem pigmentation in F₂ plants. Reciprocal crosses were performed with two genotypes, AC 2969 (kabuli) and ICC 4969 (desi), to generate F₁ and F₂ plants. The results indicated hybrid vigor (heterosis) for yield in F₁ plants and better performance of F₂ plants. Yield and yield components of some lines in F₂ were superior to the best parent, indicative of transgressive segregation. In particular, the presence of double podding (‘s’ allele) significantly increased yield in some of the transgressive segregants. Expressivity and penetrance of the ‘s’ allele depends on the background of the female parent. Some of the double podding progeny had greater seed yields than those of the single podding progeny and greater seed yields than the best parents. Double podding, stem pigmentation, and pink flowers each appears to be governed by a single recessive gene. Stem pigmentation and pink flowers appear to be linked traits that depend on the genetic background of the crossed chickpeas. Taken together, our studies of reciprocal crosses of kabuli and desi chickpeas clearly showed that yield could be improved by selection for transgressive phenotypes that have double podding.     

Epistasis in an Andean × Mesoamerican cross of common bean

The objective of this investigation was to check if epistasis is present in Andean × Mesoamerican beans crosses using triple test cross (TTC) method. The parents of the segregating population were Carioca–MG (Mesoamerican) and BRS Radiante (Andean). In July 2005, F₂ progenies (backcrossed with the parents and F₁ generation) were evaluated at two locations for three characters: number of pods plant⁻¹, number of grains plant⁻¹ and grain weight plant⁻¹. The presence of epistasis was detected for all yield components. In the partitioning of epistasis in additive x additive (i) and dominant x dominant (j) and dominant × additive (l) it was observed that, for the traits number of pods/plant and number of grains/plant, only epistasis of the type (j) + (l) were significant. For the trait grain mass/plant, all types of epistasis were significant.     

QTL × genetic background interaction: predicting inbred progeny value

Failures of the additive infinitesimal model continue to provide incentive to study other modes of gene action, in particular, epistasis. Epistasis can be modeled as a QTL by genetic background interaction. Association mapping models lend themselves to fitting such an interaction because they often include both main marker and genetic background factors. In this study, I review a model that fits the QTL by background interaction as an added random effect in the now standard mixed model framework of association analyses. The model is applied to four-generation pedigrees where the objective is to predict the genotypic values of fourth-generation individuals that have not been phenotyped. In particular, I look at how well epistatic effects are estimated under two levels of inbreeding. Interaction detection power was 8% and 65% for pedigrees of 240 randomly mated individuals when the interaction generated 6% and 20% of the phenotypic variance, respectively. Power increased to 21% and 94% for these conditions when evaluated individuals were inbred by selfing four times. The interaction variance was estimated in an unbiased way under both levels of inbreeding, but its mean squared error was reduced by 40% to 70% when estimated in inbred relative to randomly mated individuals. The performance of the epistatic model was also enhanced relative to the additive model by inbreeding. These results are promising for the application of the model to typically self-pollinating crops such as wheat and soybean. The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

Performance of upland coloured cotton germplasm lines in line × tester crosses

Anthracnose is a serious disease affecting dry bean production especially in the cool highland areas worldwide. The objective of this research was to study the inheritance of anthracnose resistance in market-class dry beans. A complete diallel set of crosses was generated from nine diverse parents comprising six resistant and three susceptible to anthracnose. The F₁ and F₂ crosses and parents were artificially inoculated with Colletotriclum lindenumthianum Race-767 in a growth room. There was significant variation for anthracnose resistance among genotypes. General combining ability (GCA) and specific combining ability effects were significant for resistance, indicating importance of both additive and non-additive effects, respectively. Preponderance of GCA effects (66%) suggested that additive effects were more important than non-additive effects (24%), which were also reflected by high heritability estimates (70%), and suggested that simple selection or backcrossing would be useful for improving the resistance in market class varieties. The study was not conclusive on whether epistatic gene action played a major role, but if available it might have biased the dominance gene effects. Reciprocal effects (10%) were not significant (P > 0.05), suggesting that cytoplasmic genes did not play a major role in modifying anthracnose resistance. Parental lines G2333, AB136, NAT002, and NAT003 showed highly negative GCA effects qualifying them as suitable parents for transferring resistance genes to their progenies. A few major genes, 1–3, displaying partial dominance conditioned anthracnose resistance, suggesting a possibility of using marker-assisted selection to improve anthracnose resistance in market-class dry beans.     

Mapping QTLs associated with Fusarium-damaged kernels in the Nanda 2419 × Wangshuibai population

Fusarium head blight (FHB), or scab, is a devastating wheat disease worldwide, reducing both grain yield and quality. The percentage of Fusarium-damaged kernels (FDK) directly reflects the damage level caused by scab on wheat grains and its variation represents the so-called type IV scab resistance in germplasm. To identify genes governing type IV resistance and investigate its relationship with other scab resistance types, we mapped QTLs associated with percent FDK using data from three different field evaluations of the recombination inbred line (RIL) population derived from the susceptible cultivar Nanda 2419 × the scab-resistant cultivar Wangshuibai. Five QTLs related to percent FDK were identified in at least two different trials, for which Wangshuibai contributed four of the resistance alleles. Most of the FDK-related QTLs, including the three with larger effects, QFdk.nau-2B, QFdk.nau-3B and QFdk.nau-4B, mapped to intervals associated with either type IV resistance or type II resistance. Moreover, most of the major type I and type II resistance QTLs detected previously were associated with type IV resistance, suggesting that resistance to initial infection and disease spread play major roles in conditioning less FDK. Therefore, breeders have options to choose inoculation methods based on their expertise and resources without risking significant loss of information when using percent FDK as the disease index. The most useful scab resistance QTLs for breeding would be those with stable influences on FDK and/or deoxynivalenol (DON) accumulation besides the initial infection and disease spread. Chunjun Li and Huilan Zhu contributed equally to this work.     

Parental effects on the performance of cultivated × wild species hybrids in potato

Valuable genetic diversity in diploid wild Solanum species can be accessed through crosses to haploids (2n = 2×) of the tetraploid cultivated potato, Solanum tuberosum. Haploid-wild species hybrids segregate for the ability to tuberize in the field. In addition, they vary in male fertility, vine size, stolon length, and tuber size. In this study, three haploids were crossed with nine diploid wild Solanum species and 27 hybrid families were evaluated in the field for two years. The proportion of male fertile hybrid clones varied depending on the wild species parent. A large effect of the female parent was detected for vine size, stolon length, tuber size, percent tuberization, and percent plants selected for agronomic quality. An exceptional haploid (US-W4) was identified for the production of agronomically desirable haploid-wild species hybrids. In hybrids derived from US-W4, differences among wild species parents were observed for agronomic quality. Superior hybrids were produced by S. berthaultii and S. microdontum. Reciprocal crosses were evaluated for a subset of families. When the wild species was used as the female parent, male fertility was restored, but tuberization and tuber size were reduced. Careful selection of both haploid and wild species parents can result in a large proportion of fertile, agronomically desirable hybrid offspring.     

Phenotypic segregation and relationships of agronomic traits in Monastrell × Syrah wine grape progeny

The aim of this work was to study the phenotypic segregation of different agronomic and fruit quality traits, and their relationships, in Monastrell × Syrah wine grape progeny. Twenty-two agronomic traits were evaluated and compared for three consecutive years in this progeny. The results show the phenotypic diversity existing in a cross between two different wine grape cultivars. Most of the phenological, productive, morphological, and enological parameters evaluated displayed continuous variation within the progeny, suggesting a polygenic inheritance. Some correlations between traits were detected by the Spearman correlation test, although high coefficients were not found for most of them. Cluster analysis of the progeny grouped the hybrids based on criteria with significance for wine grape breeding. Also, we investigated the relationship between the skin color and total content of anthocyanins with the VvmybA genotype, using the CAPS (Cleaved Amplified Polymorphic Sequence) marker 20D18CB9. The results show that hybrids with two copies of the functional color allele tend to have increased anthocyanins content. Based on this study, 14 genotypes were pre-selected from the breeding population for additional quality studies.     

Development of advanced fragrant rice lines from MR269 × Basmati 370 through marker-assisted backcrossing

Fragrance in rice is an appealing attribute to consumers. The increasing demand for fragrant rice highlights the need to develop fragrant rice variety that suit the preference of local consumers in addition to reduce fragrant rice imports. Marker-assisted backcrossing (MABC) was employed to develop advanced fragrant rice lines from the cross between MR269 and Basmati 370. MR269 is a Malaysian high-yielding rice variety but non-fragrant and was used as recurrent parent whereas Basmati 370 is a well-known fragrant traditional rice variety and was used as donor parent for the fragrance gene. Two generations of backcrosses and a generation of selfing were conducted to introgress the fragrance gene and restore the recurrent parent genome in the backcross progenies. As a result, 14 advanced fragrant rice lines were developed. These advanced fragrant rice lines carried homozygous alleles for the fragrance gene, similar to Basmati 370. The average recovery of recurrent parent genome was 88.4%. Besides being fragrant, the advanced fragrant rice lines also had most of the morphological and agronomical traits similar to MR269. Grain quality of the advanced fragrant rice lines in terms of gelatinization temperature, amylose content and gel consistency are also similar to both parents. Besides, the advanced fragrant rice lines had 2-acetyl-1-pyrroline content similar to Basmati 370. MABC approach applied in this study has successfully introgressed the fragrance gene and accelerated the recovery of recurrent parent genome in advanced fragrant rice lines, therefore these lines can be delivered to the farmers and consumers for use in due time.     

Phenotypic correlations, G × E interactions and broad sense heritability analysis of grain and flour quality characteristics in high latitude spring bread wheats from Kazakhstan and Siberia

Grain and flour samples of 42 high latitude spring bread wheat genotypes from Kazakhstan and Siberia evaluated in a multi-location trial were analyzed for grain concentrations of protein, zinc (Zn) and iron (Fe), as well as flour quality characteristics. The genotypes showed high grain protein concentrations (14–19%), but low dough strength was a common feature for most of them. Significant positive correlations were found between grain protein and flour protein, gluten, gliadin, gli/glu ratio, Zn, and Fe contents. Grain protein was also correlated positively with hardness, sedimentation, farinograph dough development time (DDT), stability time and ash content. Grain Fe concentration was positively associated with sedimentation, stability time, water absorption and valorimeter value, suggesting that improvements in micronutrient concentrations in the grain parallels enhancement in gluten strength. Interestingly, glutenin content correlated negatively with the concentrations of grain and flour protein, gluten, and minerals; and also with gluten deformation index (IDK), DDT, and stability time. Conversely, gliadin content showed strong positive correlations with the concentrations of grain and flour protein, gluten, and minerals. Gliadin also correlated positively, but in lesser magnitude, with DDT, stability time and IDK. Environment and G×E interaction were important sources of variation for some quality characteristics. This was reflected in the low broad sense heritability (H) values for traits related to flour strength, such as sedimentation, IDK, stability time and gliadin content. Breeding strategies, including three testing locations at the advanced selection stages, are adequate for the enhancement of most of the quality traits, but faster improvement in flour strength could be achieved with a larger number of locations.     

Phenotypic diversity and relationships of fruit quality traits in inter-specific almond × peach backcrosses breeding progenies

Nineteen agrochemical traits of 20 almond inter-specific backcrosses progenies were evaluated and compared for three consequence years to find out their phenotypic diversity and determine the relationships of fruit quality traits in almond × peach backcrosses breeding progenies. The variation was observed for traits of phenology parameters (blooming time, ripening time), Physical parameters (fruit weight, width, height, shape, thickness, skin pubescences, colour and flower type), chemical parameters (total sugar content, soluble solids content and acidity) and sensory parameters (attractiveness, taste, and flavor) and yield. Many fruit characteristics that are important to breeders are present in this collection. A high variability was found in the evaluated almond progenies and significant differences were found among them in all studied quality attributes. Year-by-year variations were observed for majority of traits. A significant correlation was found among the fruit height, fruit width, skin pubescences and yield. Fruit height showed a significant positive correlation with fruit weight and fruit thickness and some other traits and a negative correlation with the titratable acidity, skin pubescences and fruit flavour. A high negative correlation was found between the fruit weight and titratable acidity (?0.8). Low coefficients were got between the flower colour and skin pubescences. In addition, principal component analysis it possible to established similar groups of genotypes depending on their quality characteristics and to study relationships among pomological traits in almond progenies evaluated.     

Intergeneric hybrid between Chrysanthemum × morifolium and Artemisia japonica achieved via embryo rescue shows salt tolerance

Using embryo rescue, we generated an intergeneric hybrid between Chrysanthemum × morifolium ‘Maoyan’ and Artemisia japonica Thunb. Cytological tests confirmed that regenerated plantlets were all genuine hybrids possessing 45 chromosomes, with 27 chromosomes inherited from C. × morifolium (2n = 6x = 54) and the other 18 derived from A. japonica (2n = 4x = 36). Hybrid plant flowered normally. The shape and color of the hybrid flowers and leaves resembled those of chrysanthemum, while leaf width, leaf length, plant height, and inflorescence diameter were intermediate between those of the parents. Hybrid plant had higher levels of chlorophyll and free proline, and lower concentrations of malondialdehyde and Na⁺, than the maternal parent (C. × morifolium), and these levels were correlated with the hybrid’s enhanced salt tolerance. These results clearly demonstrate that intergeneric hybridization is an effective method of cultivar improvement in chrysanthemum.