Intracultivar selection for seed quality of soybeans in an ultra-low-density selection model (Honeycomb Selection Designs)

Selecting genotypes that combine high productivity with high seed quality is a challenge. The exploration of intracultivar genetic variation is an alternative to significantly increase the annual genetic gain and maximize the selection efficiency for both characteristics. The present study aimed to identify intracultivar variation to improve the seed quality of soybean genotypes derived from the commercial cultivar BRS 284, selected using the HSD (Honeycomb Selection Designs) model. Soybean genotypes selected for two years from two environments with contrasting edaphoclimatic characteristics, according to the principles of the HSD selection model, were cultivated under competition by using the experimental model in randomized blocks with four replicates and evaluated regarding the productivity and physiological quality of seeds. The results showed that genotype 284-3 presented a greater mass of 100 seeds, germination, vigour after accelerated ageing test, seedling emergence and emergence speed index than the other genotypes in both environments, with no significant difference in the standard cultivar regarding seed yield. The HSD method was an efficient selection method to identify intracultivar variation to improve cultivar performance.

Γενεαλογική και μαζική επιλογή για απόδοση σε πληθυσμό φακής υπό συνθήκες χαμηλής πυκνότητας και χαμηλών εισροών και η σχέση της έντασης επιλογής με την παραγωγικότητα σε σπόρο και το επίπεδο ανοχής των φυτών σε ιούς

During this work the genetic variation within a cultivated lentil landrace wasexploited through mass and pedigree honeycomb selection. The aim was toinvestigate the efficiency of the honeycomb selection method in the management ofthe planting stock relative to its load in seed borne viruses, the ability to select forvirus-free lines and possibly isolate resistant/tolerant to viruses lines, as well as theprospects of sowing monogenotype or polygenotype lentil varieties under low inputconditions.A non-replicated (NR-0) honeycomb experiment was established in the region ofOrestiada, Greece, during the 2006-2007 season, at the low density of 1,2 plants/m2.Fifteen plants were selected for high grain yield to form as many 1st generation lines.Additionally, the application of five different intensities of selection led to five 1stgeneration populations. In 2007-08, progeny evaluation was conducted in an R-21experiment and three lines were isolated based on the genotype crop yield potential,which is defined by the progeny yield potential index and coefficient of homeostasis.From these superior three lines we selected the nine plants showing the highest cropyield potential (formula A) and the three plants with the highest absolute yield, whilethree more high yielding plants were selected from other lines with low crop yieldpotential, thus leading to 15 2nd generation lines. In addition, five different intensitiesof selection were applied to form an equal number of 1st generation populations. In2008-09, progeny evaluation of the 2nd generation lines was conducted in an R-21experiment. At the same time, the 1st generation selections were evaluated in densestand conditions according to the randomized complete-block (RCB) design at anearby field. Based on coefficient of yield within the ring 11 plants were selected thatled to 11 3rd generation lines and one new population consisting of 2nd generationsline seeds. In 2010-11, progeny evaluation of the 3rd generation selections wasconducted in an R-13 experiment, while nearby 2nd generation selections wereevaluated in dense stand conditions, in a RCB experiment.During the first year of experimentation, the severe infection by seed-borneviruses resulted in low yield as well as unsatisfactory results for the rest of theparameters calculated. Several plants in the field exhibited viral-disease-like symptoms and a vast number of them died. This didn’t allow the application of thebreeding selection criteria, so that the selection was only based on the absolute plantyield. ELISA tests detected only the PSbMV in the original population.The selection of symptomless plants from the original population in the absenceof competition proved an efficient method for improving the sanitary status of theplanting stock, since the 2nd generation populations yielded higher compared to theoriginal population by 16% in the absence of competition and 5,7% in farming densitycondition. Moreover, a significant positive linear correlation was found between thenumber of the selected plants and the number of them found positive for the BYMV.The 1st generation lines 8, 2 and 15 were selected in the absence of competitiondue to their high crop yield potential and were used to derive the 2nd generation lines.Lines with low coefficient of homeostasis were positive for virus presence. On theother hand, line 8 and the lines deriving from this had high coefficient of homeostasisand escaped virus infection. The coefficient of homeostasis seems to be an effectivecriterion for revealing a putative presence of seed borne virus infection in the linesunder evaluation. The importance of this criterion is moreover demonstrated by theselection of line 15 according to its value that later produced promising 2nd and 3rdgeneration lines.Four 2nd generation lines deriving from line 8 yielded significantly higher than theoriginal population in the absence of competition by 81 to 139%. The application ofthe ECYP as line selection criterion proved efficient for the identification of highyielding and free from virus infection genotypes. In contrast, lines selected only fortheir high yield regardless of their crop yield potential failed to exhibit stability ofperformance.The 3rd generation selections had low CV most probably due to the improvementof the planting material sanitary status, since seed-borne viruses were successfullyremoved and possibly tolerant/resistant to viral diseases genotypes resulted in lowpressure from virus infections. The crop yield potential recorded in this generationcompared to the progress observed in the previous generations indicates that geneticstability has been achieved.The lines which were distinguished due to crop yield potential (ECYP), respondedpositively to the selection and progeny behavior showed that the equation can be a powerful tool for creating inbred lines that are characterized by stability and highproductivity. Eventually, the application of the honeycomb method selection resultedin lines with satisfactory performance under farmer’s conditions, since three 2ndgeneration lines had higher yield compared to the original population by 22 to 24%.Under typical plant density conditions, the 1st generation heterogenouspopulations showed higher yield than the original population compared to the linesby 7,2 and 5,6% respectively. In contrast, the 2nd generation lines yielded higher thanthe populations by 9,4 and 5,7% compared to the original population respectively.Thus, the answer to the question whether monogenotype or polygenotype varietiesshould be recommended for cultivation requires further investigation.

Relationships of grain carbon isotope discrimination (Δ) and ash content with yield and quality in dry bean

SUMMARYDry bean (Phaseolus vulgaris L.) is a traditional crop of north-western Macedonia, Greece, where two landraces (plaki Prespas and Chrisoupoli) in particular are grown. The aim of this study was to test whether the grain carbon isotope discrimination (Δ) and ash content (ASH) are related to grain yield (GY), protein content (PC) and mean grain weight (MGW) in dry bean. As a part of a honeycomb selection programme, 21 genotypes (19 lines derived via intra-landrace honeycomb selection for single plant yield at low density plus the two original populations) were grown at two densities, 1·2 and 4·8 plants/m2 under non-limiting water conditions in a glasshouse and in the field. Genotypes differed significantly for Δ, ASH and PC under the low density. In the dense stand, genotypes differed significantly only for ASH and PC. The environment (glasshouse or field conditions) affected all the traits significantly. Neither Δ nor ASH showed strong or consistent relationships with GY and thus, they cannot serve as reliable, indirect selection criteria for GY. Strong, negative relationships between Δ and PC were found especially in the dense stand, confirming analogous results in C3 cereals. Inconsistent genotypic ranking for grain physiological traits under the different densities and environments was indicative of large genotype×environment interaction. Genotypes performed consistently for GY and MGW under both densities, showing the strong stability of these traits.

Variability within cotton cultivars for yield, fibre quality and physiological traits

SUMMARYSelection within elite cotton cultivars is ineffective; it is believed that they are genetically homogeneous. Research in other crops, however, has verified significant intra-cultivar variation based either on phenotypic differentiation or molecular analysis techniques. The present study primarily investigated possible intra-cultivar variation for seedcotton yield. Honeycomb selection within three elite cotton cultivars, on the basis of single-plant seedcotton yield and under the ultra-low density of 1·2 plants/m2, was performed. From each cultivar, six selfed (hand-pollinated) plants were selected and seed of each selected plant constituted a separate line. The 18 first generation lines were evaluated in three locations at a density of 1·2 plants/m2. Within each line, the 10 selfed plants which yielded the highest were selected. Mixed seed from these selected plants constituted the respective second generation line. Offspring performance of the 18 second generation lines was also tested in three locations at a density of 1·2 plants/m2. The results were indicative of intra-cultivar variation, since significant differentiation between lines of each cultivar was found for seedcotton yield per plant, averaged across two years and three locations. Additionally, significant intra-cultivar variation was found for fibre quality properties (length and micronaire, but not strength and uniformity) averaged across two years in a single location, as well as for physiological traits (leaf carbon isotope discrimination, ash content and K concentration) averaged across two years and three locations. In comparison with the original cultivars the second generation lines had higher seedcotton yields supporting the existence of exploitable genetic variation. The conclusion was that honeycomb selection in the absence of competition could be an effective technique in breeders' seed treatment in order to avoid gradual degeneration and beneficially exploit any latent or newly developed genetic variation.

Rice F1 hybrids: the breeding goal or a costly solution?

Whether to develop inbred cultivars or F1 hybrids is a dilemma faced by many rice (Oryza sativa L.) breeders. This could be partially answered if one could select superior recombinant inbred lines with an equal yielding ability and good quality traits from commercial F1 hybrids. Thus, it was attempted in this study to select superior inbred lines from 2 commercial F1 hybrids after application of honeycomb selection and panicle-to-row selection. The 2 F2 populations were advanced to F6 generation by both methods and, finally, 5 F5:6 lines with high yield potential and good grain quality were selected from each population and selection method and were tested in a randomised complete block design for 2 years in Kalochori, Thessaloniki, Greece. In each case the respective F1 hybrid and the check cultivar Strymonas were used as checks. Fourteen of the 20 lines selected by honeycomb selection and panicle-to-row selection from both populations exhibited a yielding ability that was not significantly different from the yield of the F1 hybrids in both years. Three of them, however, in 1 of the 2 years, had a significantly higher grain yield than the corresponding F1 hybrid. In addition, 6 of the above lines exhibited significantly higher values for more than 1 of the 4 quality traits (total milling yield, grain vitreosity, grain length, and grain length/width ratio) and they were not inferior for the remaining ones. It was concluded that application of combined selection for yield and quality could lead to the isolation of recombinant inbred lines with equal yielding ability and quality equal to or higher than the F1 hybrids. This, together with the higher cost associated with hybrid technology, indicates that the long-term goal of a rice-breeding program should be the production of superior inbred lines, unless hybrid production cost is low and quality is not critical for the particular market.

The effects of the genotype by environmental interaction on the fixation of heterosis in tomato

Continuous honeycomb selection and testing in the absence of competition in a single environment, resulted in the isolation of recombinant inbreds in tomato that outperformed the hybrid only in that particular environment. Alternating selection and testing in two environments (open field v. glasshouse) reduced selection efficiency, by preventing exploitation of the whole constellation of genes contributing to heterosis. Selection in the F2 generation was most critical, as evidenced by the appearance of recombinant lines outperforming the hybrid as early as in the F3 generation. Exploitable genetic variation existed in advanced generations and even after the point of achieving theoretical homozygosity (F7 generation). In the future, and in order to fully exploit the unique possibilities offered by the honeycomb methodology (control of soil heterogeneity, high selection pressures, crop yield components), selection for reduced GE interaction should be practiced simultaneously over the target environments of adaptation.

Comparative efficiency of three selection methods in Dactylis glomerata L. and Agropyron cristatum L.

Two populations, one non-improved of Dactylis glomerata and one improved of Agropyron cristatum were selected in an isolated spaced plant environment (80 cm) by three selection procedures: (1) Mass honeycomb selection (MHS), (2) pedigree honeycomb selection (PHS) and (3) pedigree honeycomb selection-combined criterion (PHS-CC). The third procedure is a between-families selection based on increased family mean and reduced family coefficient of variation (CV). Response to selection assessed in sward trials in the first and second harvest year was effective for the three procedures, which ranked PHS-CC > PHS > MHS. Evaluation was based on consistent efficiency as measured by both cloned and half-sib families. The precision of assessing progeny performance under sward conditions on the basis of single plant evaluation in the isolation environment, increased with a reduction in competition among plants, the use of moving-ring selection, and the application of high selection pressures (1·6%). The efficiency of selection between unimproved families increased when families were selected concurrently for high family mean and reduced family coefficient of variation.

The effect of honeycomb selection for grain yield on a maize population

SUMMARYStarting with the F2 generation of a single-cross hybrid, a maize population was improved from cycle 0 (= F2) to cycle 4 by mass honeycomb selection and from cycle 5 to cycle 8 by pedigree honeycomb selection. Seven half-sib families were derived from cycle 8. The grain yield of these, their corresponding S1 lines, testcrosses with B73 and diallel crosses were studied. The results showed (i) that the seven half-sib families contained half the percentage of the load of deleterious genes present in the F2 generation, (ii) that four of them outyielded their corresponding single-cross hybrids, (iii) that they could constitute an open-pollinated variety, which could be used as a source population and (iv) that they revealed different patterns for general and specific combining ability. Honeycomb selection for grain yield was successful in favouring the existing additive genetic variation in the derived families.