Changes in morphological and physiological traits associated with recurrent selection for grain yield in maize

Summary Experiments were conducted during the growing seasons of 1975 and 1976 to determine changes in morphological and physiological traits associated with recurrent selection for grain yield in maize (Zea mays L.). Four variety hybrids, BSSS(R)CO x BSCB1(R)CO, BSSS(R)C7 x BSCB1(R)C7 [from a reciprocal recurrent selection program involving Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic #1 (BSCB1)], BS12CO x B14A, and BS12C6 x B14A [from a half-sib selection program involving the open-pollinated variety Alph (BS12) and the inbred tester B14A] were grown at 59 300 and 98 800 plants/ha near Ames, Iowa We obtained data on CO₂-exchange rate (an estimate of photosynthetic rate), grain yield, grain-yield components, flowering dates, maturity traits, light interception and use, shelling percentage, harvest index, and various other plant traits.CO₂-exchange rate did not change appreciably with recurrent selection for yield. Grain yield per hectare and per plant were larger for the improved than unimproved hybrids. Grain-yield components did not change significantly with recurrent selection. Kernel weight of BSSS(R)C7 x BSCB1 (R)C7, however, was larger than that of BSSS(R)C0 x BSCB1(R)C0. Pollen-shed-to-silking interval was shorter for the improved than the unimproved hybrids, and grain-filling duration was longer in C7 x C7 than in C₀ x C₀ of the reciprocal recurrent selection program. Furthermore, improved hybrids were characterized by smaller tassels and more upright canopies. Usually, plant traits and leaf-area-related traits were similar for all hybiids.Although dry-matter productivity was similar for all hybrids, those that were improved by recurrent selection produced more grain per unit leaf area and per unit light interception. Also, BS12C6 x B14A was characterized by a higher harvest index than BS12CO x B14A.We concluded that the source (i.e., photosynthetic capacity) was not limiting grain yield in BSSS(R) x BSCB1(R) and BS12. Increased grain yields that resulted from recurrent selection were consequences of longer grain-filling duration for BSSS(R) x BSCB1(R) and increased translocation of photosynthate from source to sink for both BSSS(R) x BSCB1(R) and BS12.Journal Paper J-8953 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, Iowa. Project No. 2152.     

A factor analysis of plant variables associated with architecture and seed size in dry bean

Summary A knowledge of the biological and functional relationships among traits would be of benefit to plant breeders in the choice of traits to use for increasing efficiency of selection in a breeding program. Principal factor analysis was used to identify biological and functional relationships among dry bean (Phaseolus vulgaris L.) traits in segregating populations of a phenotypic recurrent selection program designed to introduce upright architecture into medium-sized dry bean.Two biological interpretations were assigned to factors extracted in the analysis of four seed/pod traits. The first was a size factor, loaded with seed weight and pod width, and the second a number factor, which was loaded with number of seeds per pod and pod length. Similarly, three factors were extracted from the analysis of fifteen architectural traits. The first factor was interpreted as an elongation factor, and was loaded with internode length measurements, while the second factor was interpreted as a structural factor, and was further divided into two subclasses namely, sturdiness factor and profile factor. The sturdiness factor comprised hypocotyl diameter and hypocotyl length, while the profile factor comprised branch angle and number of basal branches. The third factor which was called a reproductive factor was loaded with pod distribution traits and the number and location of nodes on which pods were borne.     

Morpho-physiological traits to complement grain yield selection under semi-arid Mediterranean conditions in each of the durum wheat types mediterraneum typicum and syriacum

Summary Some 238 landraces from Algeria and Tunisia representative of the mediterraneum typicum durum wheat type and 265 landraces from Syria and Jordan representing the syriacum type were grown in a semi-arid Mediterranean environment of Northern Syria characterized by moderate drought stress. The germplasm types were compared for mean value, level of variation and relationships with grain yield of various morpho-physiological traits possibly usable for indirect selection of best yielding materials. The syriacum germplasm showed higher yield mainly due to greater earliness of cycle, slightly longer grain filling period, shorter stature, lower early growth vigour and higher drought tolerance expressed by a visual score recorded in another, more stressful environment in the region. It also showed lower variation for all morpho-physiological characters except plant glaucousness, for which it was more variable. The wheat types differed not only for architecture but also for optima of individual morpho-physiological traits required to maximize the yield response in the given environment. Higher yield of syriacum materials was attained at same heading and three to four days delayed maturity with respect to average phenology of three well-adapted control cultivars, and it was favoured by increasing number of kernels per spike, early vigour and drought tolerance. Higher yield of mediterraneum typicum landraces was related to heading and maturity dates approaching those of the control cultivars and to increasing kernel weight, early vigour and drought tolerance. Plant stature hardly affected the yield. Both absent and strong glaucousness could confer a yield advantage in syriacum materials.     

Decentralized selection and participatory approaches in plant breeding for low-input systems

Heterogeneous environments make it difficult to apply consistent selection pressure because often it is difficult to identify a single or a few superior genotypes across all sets of conditions. However, when the target system is characterized by heterogeneity of environmental stress, varieties developed in high-yielding conditions may fail to satisfy farmers’ needs. Although this type of system is often found in marginal environments of developing countries, heterogeneous environmental conditions are also a feature of organic and low-external-input systems in developed countries. To meet the needs of these systems, breeding programs must decentralize selection, and although decentralized selection can be done in formal breeding programs, it is more efficient to involve farmers in the selection and testing of early generation materials. Breeding within these target systems is challenging, both genetically and logistically, but can identify varieties that are adapted to farming systems in marginal environments or that use very few external inputs. A great deal has been published in recent years on the need for local adaptation and participatory plant breeding; this article reviews and synthesizes that literature.     

Trial heterogeneity and variance models in the genetic evaluation of potato tuber yield

Genetic evaluation aims to identify genotypes with high empirical breeding values (EBVs) for selection as parents. In this study, 2157 potato genotypes were evaluated for tuber yield using 8 years of early‐stage trial data collected from a potato breeding programme. Using linear mixed models, spatial parameters to target greater control of localised spatial heterogeneity within trials were estimated and variance models to account for across‐trial genetic heterogeneity were tested. When spatial components improved model fit, correlations of errors were mostly small and negative for marketable tuber yield (MTY) and total tuber yield (TTY), suggesting the presence of interplot competition in some years. For the analysis of multi‐environment trials, a variance model with a simple correlation structure (with heterogeneous variances) was the most favourable variance structure fitted for TTY and PTY (per cent marketable yield). There was very little difference in model fit when comparing a factor analytic structure of order 2 (FA2) with either FA1 or simple correlation structures for MTY, indicating that simple variance models may be preferable for early‐stage genetic evaluation of potato yield.     

Genetic progress after four cycles of recurrent selection for yield and grain traits in common bean

The objective of this study was to evaluate the genetic progress after four cycles of recurrent selection in common bean. The base segregating population was obtained from 10 parents, and derived the S_0:1 and S_0:2 families that were evaluated. The S_0:3 families with higher grain yield and grain color, like the standard carioca were selected, and were intercrossed to generate the population of the following cycle. This process was repeated for four cycles. The best families were evaluated in each cycle by many generations and locations, and the five best lines of each cycle were identified. The 20 lines thus obtained were evaluated in two growing seasons, sown in July and November 2002. The grain yield (kg/ha) and grain type (scale of scores) were evaluated. Genetic progress was confirmed for both traits. The mean annual gain with selection for the grain type was 10.5% and 5.7% for grain yield, with no evidence of variability reduction in the population. These results show that recurrent selection is a good alternative for improving common bean quantitative traits.     

Indonesian mungbean landraces II. Comparison of performance,components of variance and selection for grain yield under wide row-spacing in monoculture and when intercropped with maize

Summary The possibility of testing mungbean for grain yield in monoculture in single wide-spaced row plots as an alternative to selection in intercropping with maize was investigated. Results indicated no significant genotype x planting pattern interactions and genetic correlation coefficients between grain yields in the two planting patterns were, in most cases, close to unity. It was concluded that, as far as the mungbean component in the mixture is concerned, yield selection in either of the two planting patterns is justified. Effects of single-plant and progeny selection on mungbean characteristics were also studied empirically. Lines derived from single-plant selection in monocropping or intercropping showed differences in yield, number of pods per plant and seed weight. Except for seed weight, no differential effects of progeny selection in monoculture or intercropping were observed for any characteristic.     

Comparing farmers and breeders rankings in varietal selection for low-input environments: A case study of rainfed rice in eastern India

A number of breeding institutions developed a project to assess importance of participatory plant breeding approaches for rainfed rice improvement in eastern India. The results of the first two years of participatory varietal selection are reported here. The objective was to evaluate the respective effects of participation of farmers in varietal evaluation and decentralization of varietal testing from breeding stations to farmers' fields on varietal ranking. Fields representing various hydrological situations were chosen in two to three villages at four rainfed lowland sites and one upland site. Sets of 15 to 25 varieties were tested both in farmers' fields and on-station in 1997 and 1998 and ranked by both farmers and breeders. The effect of participation was judged by comparing the rankings attributed by farmers and breeders to a given set of material in a given trial. The effect of decentralization was determined through comparisons between individual breeders' rankings across trials. Farmers' rankings were not randomly allocated, but agreement within the farmers' group was not always very strong. Except at one site, concordance among breeders' ranking was high, but, because of the limited number of breeders involved, it was seldom significant. In about two-thirds of the trials, there was a good agreement between farmers' and breeders' mean rankings. The consensus was particularly strong when severe constraints induced contrasting behavior in the genotypes. The decentralization effect appeared to be moderate, but variations due to a breeder effect were recorded. The part of genotype by environment interactions for grain yield due to location within one site and year was evaluated through various methods, showing more effect of G × E interactions at some sites than at others. Crossover interactions inducing changes in ranks represented a limited part of the yearly G × E interactions at all sites. Both farmer participation and decentralization of varietal testing in farmers' field would help in best matching the varieties to the needs, although their combined contribution would be more useful in some sites than in others. This revised version was published online in August 2006 with corrections to the Cover Date.     

Assessment of soybean yield with altered water-related genetic improvement traits under climate change in Southern Brazil

Water deficit is a major factor responsible for soybean yield gap in Southern Brazil and tends to increase under climate change. An alternative to reduce such gap is to identify soybean cultivars with traits associated to drought tolerance. Thus, the aim of this study was to assess soybean adaptive traits to water deficit that can improve yield under current and future climates, providing guidelines for soybean cultivar breeding in Southern Brazil. The following soybean traits were manipulated in the CSM-CROPGRO-Soybean crop model: deeper root depth in the soil profile; maximum fraction of shoot dry matter diverted to root growth under water stress; early reduction of transpiration under mild stress; transpiration limited as a function of vapor pressure deficit; N₂ fixation drought tolerance; and sensitivity of grain filling period to water deficit. The yields were predicted for standard and altered traits using climate data for the current (1961–2014) and future (middle-century) scenarios. The traits with greater improvement in soybean yield were deeper rooting profile, with yield gains of ≈300 kg ha⁻¹, followed by transpiration limited as a function of vapor pressure deficit and less drought-induced shortening of the grain filling period. The maximum fraction of shoot dry matter diverted to root and N₂ fixation drought tolerance increased yield by less than 75 kg ha⁻¹, while early reduction of transpiration resulted in a small area of country showing gains. When these traits were combined, the simulations resulted in higher yield gains than using any single trait. These results show that traits associated with deeper and greater root profile in the soil, reducing transpiration under water deficit more than photosynthesis, creating tolerance of nitrogen fixation to drought, and reducing sensitivity of grain filling period to water deficit should be included in new soybean cultivars to improve soybean drought tolerance in Southern Brazil.     

Feasibility of selection for traits associated with cold tolerance in rice under rapid generation advance method

Summary Variability of the hybrid population can be preserved through generations during the process of rapid generation advance (RGA). Effective selection can be done in an early generation for those traits having high heritability value like growth duration and plant height. But selection is not advantageous for traits having low heritability. Thus, selection for panicle exsertion, cold tolerance at seedling stage and panicle length would not be wise during the early generations. However, in the low temperature areas growth duration and plant height are two important factors which determine varietal suitability. As selection of these two characters are possible through RGA, it should be a standard parctice during RGA to eliminate the plants with long growth duration and select plants with optimum plant height.     

Collaborative and consultative participatory plant breeding of rice for the rainfed uplands of eastern India

We describe a participatory plant breeding (PPB) programme in rice for the rainfed uplands of eastern India. Collaborative participation (farmers grew and selected in segregating materials in their fields) and consultative participation (farmers selected among progenies in researchers' plots) were used. The PPB was started with only two crosses and, of these, Kalinga III/IR64 was the most successful and produced two released varieties: Ashoka 200F from collaborative breeding and Ashoka 228 from consultative breeding. Both yielded significantly more than control varieties, including Kalinga III, in research trials and in participatory trials in farmers' fields. Qualitative data from participatory trials was highly informative, statistically analysable, and cheaper to obtain than quantitative data. In low-yielding research-station and on-farm trials the two new upland varieties showed no significant genotype × environment interaction with the check varieties. However, in higher-yielding All India Coordinated Rice Improvement Project trials, both varieties were more adapted to low yielding environments than the national check variety. Farmers liked the varieties for their early maturity, improved lodging resistance, higher fodder and grain yield, long-slender grains and excellent cooking quality. Before certified seed production, farmer groups have produced large quantities of seed that have spread widely through informal channels. The returns from PPB, compared to conventional breeding, were higher because it cost less, the genetic gains per year were higher, and the benefits to farmers were realised earlier. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification of QTLs associated with spring vegetative budbreak time after dormancy release in pear (Pyrus communis L.)

Dormancy release is greatly affected by chilling unit (CU) accumulation. Lack of CU has a major impact on spring vegetative budbreak (VB). To understand the genetic mechanism governing the chilling requirement (CR), we conducted a QTL analysis of VB date in F₁ population, derived from a cross between ‘Spadona’ (low CR) and ‘Harrow Sweet’ (high CR). Using a unique methodology of tree mobility, replicates of the same genotypes were exposed during the winter, over two consecutive years, to climates that differ greatly in their CU and to the same heat conditions to induce VB, in order to evaluate CR genetic impact and to distinguish it from the heat factor. Broad‐sense heritability within locations ranged from 0.62 to 0.66. Due to a strong impact of GxE interaction, it was reduced to 0.46 for the overall mean. We examined the previously discovered apple QTLs detected in linkage groups (LG) 9 and 8, based on the synteny between the species. Our analysis confirms significant QTLs in LG8 (R² = 12%–24%) and LG9 (R² = 20%–38%) for all locations and years     

Genomic regions associated with grain yield and aspects of post-flowering drought tolerance in pearl millet across stress environments and tester background

A pearl millet mapping population from a cross between ICMB841 and 863B was studied for DNA polymorphism to construct a genetic linkage map, and to map genomic regions associated with grain and stover yield, and aspects of drought tolerance. To identify genomic regions associated with these traits, mapping population testcrosses of 79 F₃ progenies were evaluated under post-flowering drought stress conditions over 2 years and in the background of two elite testers. A significant genotype × drought stress treatment interaction was evident in the expression of grain and stover yield in drought environments and in the background of testers over the 2 years. As a result of this, genomic regions associated with grain and stover yield and the aspects of drought tolerance were also affected: some regions were more affected by the changes in the environments (i.e. severity and duration of drought stress) while others were commonly identified across the drought stress environments and tester background used. In most instances, both harvest index and panicle harvest index co-mapped with grain yield suggesting that increased drought tolerance and yield of pearl millet that mapped to these regions was achieved by increased partitioning of dry matter from stover to the grains. Drought stress treatments, years and testers interactions on genomic regions associated with grain and stover yield of pearl millet are discussed, particularly, in reference to genetic improvement of drought tolerance of this crop using marker-assisted selection.     

Optimising potato breeding. I. The genotypic,environmental and genotype-environment coefficients of variation for tuber yield and other traits in potato (Solanum tuberosum L.) under different experimental conditions

Summary Coefficients of variation for genotypic differences, genotype-location, genotype-year and genotype-location-year interaction were computed from reported data of potato trials in order to use them in a decision support system. The obtained coefficients of variation not only varied considerably between traits, but also between trials within traits. It is argued that only parameter values representative for the pertaining breeding situation should be used for optimising a selection programme.