Achievements and future directions of sunflower breeding

Sunflower (Helianthus annuus L.) is among the most important oil crops in the world. Due to its low to moderate production requirements, high oil quality, protein content, and utilization of all plant parts, it is grown on about 14 million ha. The major sunflower-producing countries in the world are the Soviet Union, Argentina, China, the United States, France, Spain, Romania, Turkey and Hungary. Sunflower became an oil crop around the end of the 19th century, when ‘popular selection’ was practiced in several parts of Russia to improve sunflower populations grown at that time.

The most important contributions to the development of sunflower were made by Pustovoit and Jdanov in the Soviet Union, who increased the oil concentration in sunflower seed above 500 g kg⁻¹. Leclercq of France discovered the first usable sourccytoplasmic male sterility in a cross H. petiolaris Nutt. × H. annuus L. and Kinman of the United States developed fertility restorer lines RHA 265 and RHA 266 which allowed practical development of sunflower hybrids.

When starting a breeding program, it is useful to design a model of the desired hybrid and then strive to develop the envisaged model as closely as possible. It is also advisable to direct breeding efforts toward a limited number of economically important traits. These should include: (1) components of seed and oil yield: the number of seeds per plant, test weight, 1000-seed weight, low husk content and high oil concentration in the seed; (2) architecture of the sunflower plant: plant height, head size and shape, angle of the head, leaf area and leaf canopy; (3) increased harvest index: oil quality, protein concentration and quality, early maturation, short stem and uniform height; and (4) resistance to diseases and drought using wild sunflower species.

Mass selection, a method of selecting desirable plants from a population on the basis of phenotypic traits, is still in effective method in sunflower breeding. Recurrent selection appears to be a promising method of increasing the frequency of desirable genotypes in a source population.

Genetic variability of the cultivated sunflower may be increased by interspecific hybridization with wild sunflower species. The inclusion of wild species programs is difficult because of differences in chromosome number (2n, 4n, 6n) and incompatibility. These obstacles have been overcome by embryo culture and other tissue culture techniques. Generally, the use of new technologies in sunflower breeding is imperative, particularly in regard to the introduction of resistance genes to diseases and insect pests.     

The effect of water stress on the yielding capacity of potato crops and subsequent performance of seed tubers

Summary The effect of water stress on yielding capacity of potatoes was studied in 3 years using four different levels of soil water potential (0.7, 1.9, 3.4 and 7.8 atm.) in experiments in specially adapted structures that excluded uncontrolled water supply. Seed tubers from these crops were planted in the following years to investigate effects of water stress on their subsequent performance. Limited soil moisture availability decreased yield and the number and size of tubers. The growing period was shortened by 1–4 weeks and dormancy period by 2–8 weeks. In the following year, seed produced under conditions of moisture stress gave plants with 20% fewer stems. 24–33% less yield, 18–22% fewer tubers and 19–22% fewer large tubers than plants from seed produced under abundant water supply. It is concluded that the yield potential of seed tubers can be improved by careful attention to the availability of soil moisture during their production.     

High altitude population of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> is more plastic and adaptive under common garden than controlled condition

Background

Population differentiation and their adaptation to a particular environment depend on their ability to respond to a new environment. This, in turn is governed to an extent, by the degree of phenotypic plasticity exhibited by the populations. The populations of same species inhabiting different climatic conditions may differ in their phenotypic plasticity. Himalayan populations of Arabidopsis thaliana originating from a steep altitude are exposed to different climatic conditions ranging from sub-tropical to temperate. Thus they might have experienced different selection pressures during evolution and may respond differently under common environmental condition.

Results

Phenotypic plasticity and differentiation of natural populations of A. thaliana grown under common garden and controlled conditions were determined. A total of seventeen morphological traits, their plasticity, association between traits and environment were performed using 45 accessions from three populations. Plants from different altitudes differed in phenotypes, their selection and fitness under two conditions. Under both the conditions lower altitude population was characterized by higher leaf count and larger silique than higher and middle altitude population. Flowering time of high altitude population increased while that of low and medium altitude decreased under controlled condition compared to open field. An increase in seed weight and germination was observed for all the population under open field than controlled. Rosette area was under divergent selection in both the condition. The heritability of lower altitude population was the highest under both the conditions, where as it was the least for higher altitude population further indicating that the high altitude populations are more responsive towards phenotypic changes under new environmental conditions. Ninety-nine percent of variability in traits and their plasticity co-varied with the altitude of their origin. The population of high altitude was more plastic and differentiated as compared to the lower altitude one.

Conclusions

Arabidopsis thaliana population native to different altitudes of the west Himalaya responds differently when grown under common environments. The success of high altitude population is more in common garden than the controlled conditions. The significant variability in phenotype and its association with altitude of origin predicts for non-random genetic differentiation among the populations.

     

Role of functionally dominant species in varying environmental regimes: evidence for the performance-enhancing effect of biodiversity

ABSTRACT: BACKGROUND: Theory suggests that biodiversity can act as a buffer against disturbances and environmental variability via two major mechanisms: Firstly, a stabilising effect by decreasing the temporal variance in ecosystem functioning due to compensatory processes; and secondly, a performance enhancing effect by raising the level of community response through the selection of better performing species. Empirical evidence for the stabilizing effect of biodiversity is readily available, whereas experimental confirmation of the performance-enhancing effect of biodiversity is sparse. RESULTS: Here, we test the effect of different environmental regimes (constant versus fluctuating temperature) on bacterial biodiversity-ecosystem functioning relations. We show that positive effects of species richness on ecosystem functioning are enhanced by stronger temperature fluctuations due to the increased performance of individual species. CONCLUSIONS: Our results provide evidence for the performance enhancing effect and suggest that selection towards functionally dominant species is likely to benefit the maintenance of ecosystem functioning under more variable conditions.     

Soil Weed Seed Banks and Weed Management

Abstract

Studies of soil weed seed banks are of relatively recent origin considering their importance as sources of diversity and continued occupation of many types of habitats, including agroecosystems. The management of weed seed banks is based on knowledge and modification of the behavior of seeds within the soil seed bank matrix. The behavior of seeds defines the phenotypic composition of the floral community of a field. Selection and adaptation over time have led to the highly successful weed populations that exploit resources unused by crops. The weed species infesting agricultural seed banks are those populations that have found successful trait compromises within and between the five roles of seeds: dispersal and colonization, persistence, embryonic food supply, display of genetic diversity, and as a means of species multiplication. Diverse weed seed populations provide seed banks the opportunity to exploit any change in conditions to ensure their enduring survival and spread. The soil seed bank matrix is the spatial arrangement of environmental and physical factors over time. The behavior of soil seed banks at any level of biological, spatial, or temporal organization is a consequence of the accumulated, emergent behavior at lower levels of organization. Weed seed behavior arises from their sensitivity to environmental conditions within the physical structure of the soil seed bank. This sensitivity is reflected in changes of short duration (e.g., germination), during the annual life cycle, over multiple years (e.g., population shifts), and over evolutionary time. Understanding the processes that drive and control seed behavior will allow us to manipulate and manage weed seed banks in an economic and sustainable manner. This knowledge will allow us to implement improved, more informed, weed management systems and strategies. Important weed bank management strategies include prevention of seed introduction on farm, acquisition of weed biology information (including predictive tools), decision making about weed seed infestation levels and their implementation (eradication, reduction, tolerance), weed seed population shifts (within the seed bank, between species, increased diversity), and manipulations encouraging beneficial weed species. Environmental modification and changes in cropping systems can also be of considerable strategic importance in weed management.     

Long-term approaches for the control of Striga in cereals: field management options

Farmers in Africa have limited resources to invest in Striga control practices and longer term, low-input approaches are needed. Long-term Striga control approaches focus on controlling the production of new Striga seeds and on reducing the number of seeds in the soil. Several seasons of hand weeding are required before the beneficial effect on the cereal crop can be observed. Rotations with trap crops can reduce Striga seed banks but selection of a rotation crop should be based on socio-economic factors such as market value in addition to whether or not it can stimulate Striga seeds to germinate. Striga seed banks can be readily reduced in suppressive soils. Organic matter and fertilizer additions may help induce suppressiveness. Extension of long-term Striga control approaches requires intensive interaction with farmers.     

The effectiveness of using a minituber crop for selection of agronomic characters in potato breeding programmes

Summary Performance of 20 potato genotypes was studied for seven agronomic characters in crops raised from minitubers and normal seed tubers. Correlation coefficients were computed between minituber crop and normal seed crop in order to study the selection efficiency at minituber crop level. The performance of normal seed crop was significantly better than the minituber crop for various characters including tuber yield and its components. Correlation coefficients between minituber and normal seed crop were significant for various characters except number of stems and number of tubers. Highest correlation coefficient (r=0.86) was for tuber yield followed by average tuber weight (r=0.67) and number of nodes (r=0.63). The results suggest that selection for tuber yield can be practised at the minituber crop level in potato breeding programmes     

When and where a seed mix refuge makes sense for managing insect resistance to Bt plants

Planting of a separate structured refuge for Bt crops as part of an insect resistance management (IRM) strategy to delay resistance evolution is the most common method of refuge deployment but this strategy depends on growers planting a refuge. A seed mix refuge interspersed with a pyramided Bt product is an alternative strategy that addresses the risk of growers not planting a refuge. However, concerns exist regarding how larval movement between Bt and non-Bt plants might influence resistance evolution in a seed mix field. To understand when seed mixes are an appropriate IRM strategy, a deterministic model run probabilistically was used to examine the evolution of Bt resistance in seed mix and structured refuges under varying levels of Bt efficacy, pest fitness, refuge size, larval movement, movement penalty and grower compliance. Results from modeling simulations show that the addition of a second and third Bt toxin can delay resistance evolution longer than a single toxin, making a seed mix refuge strategy a viable option where refuge compliance is a concern. In seed mixes, resistance was shown to evolve faster compared to a responsibly implemented structured refuge and evolved fastest in seed mixes when larval movement rates were high. However, when mortality from larval movement was included in model simulations, the selection pressure from Bt was reduced and two or three Bt-pyramids with a 5% seed mix refuge were at least as durable as the same products with a 5% structured refuge, depending upon refuge compliance. These simulations show that, across a range of conditions, seed mix refugia provide an effective alternative IRM tactic for delaying resistance evolution. Under some conditions use of seed mix refugia may be a superior IRM tactic leading to longer delays to resistance, and greater durability, compared to structured refugia and is a risk adverse tactic in situations when no refuge is planted.     

Gum and protein enrichment from sicklepod (Cassia obtusifolia) seed by fine grinding and sieving

Sicklepod (Cassia obtusifolia) is a weed species that has contaminated soybean and other crops. Although sicklepod continues to be a problem weed, the advent of herbicide-resistant soybeans has reduced the problem somewhat in the last few years. Sicklepod seed contains a gum of commercial interest in addition to protein and fat. An inexpensive process to enrich gum and protein contents of sicklepod seed is desirable for increased utilization and further processing. This study was conducted to determine whether fine grinding and sieving of sicklepod seed into separate fractions according to particle size could enrich gum and protein. Sicklepod seed was finely ground in a pin mill at different speed, and the resulting ground seed was separated into various fractions according to particle size. Gum content increased with particle size, and protein content decreased with particle size. Fine grinding and sieving of sicklepod seed can enrich gum in the fraction with largest particle size and can enrich protein in the fraction with smallest particle size. Fine grinding and sieving of sicklepod seed can make further processing more economical.     

花生野生种及其在花生抗病中的利用

花生是世界上重要的油料作物之一。与栽培种相比,花生野生种具有较高的遗传多样性,能够适应一系列复杂环境,是抵抗生物胁迫和非生物胁迫的重要基因来源。多项研究表明,花生野生种对根结线虫病、晚斑病和锈病具有较高抗性。本文综述了野生花生的种类以及花生栽培种起源种相关研究进展,总结了野生花生对花生病害的抗性以及在育种中应用。结合花生基因组学最新研究,展望了花生野生资源的利用前景。     

The intrinsic plasticity of farm businesses and their resilience to change. An Australian example

This paper examines the idea that plasticity in farm management introduces resilience to change and allows farm businesses to perform when operating in highly variable environments. We also argue for the need to develop and apply more integrative assessments of farm performance that combine the use of modelling tools with deliberative processes involving farmers and researchers in a co-learning process, to more effectively identify and implement more productive and resilient farm businesses.In a plastic farming system, farm management is highly contingent on environmental conditions. In plastic farming systems farm managers constantly vary crops and inputs based on the availability of limited and variable resources (e.g. land, water, finances, labour, machinery, etc.), and signals from its operating environment (e.g. climate, markets), with the objective of maximising a number of, often competing, objectives (e.g. maximise profits, minimise risks, etc.). In contrast in more rigid farming systems farm management is more calendar driven and relatively fixed sequences of crops are regularly followed over time and across the farm. Here we describe the application of a whole farm simulation model to (i) compare, in silico, the sensitivity of two farming systems designs of contrasting levels of plasticity, operating in two contrasting environments, when exposed to a stressor in the form of climate change scenarios;(ii) investigate the presence of interactions and feedbacks at the field and farm levels capable of modifying the intensity and direction of the responses to climate signals; and (iii) discuss the need for the development and application of more integrative assessments in the analysis of impacts and adaptation options to climate change.In both environments, the more plastic farm management strategy had higher median profits and was less risky for the baseline and less intensive climate change scenarios (2030). However, for the more severe climate change scenarios (2070), the benefit of plastic strategies tended to disappear. These results suggest that, to a point, farming systems having higher levels of plasticity would enable farmers to more effectively respond to climate shifts, thus ensuring the economic viability of the farm business. Though, as the intensity of the stress increases (e.g. 2070 climate change scenario) more significant changes in the farming system might be required to adapt. We also found that in the case studies analysed here, most of the impacts from the climate change scenarios on farm profit and economic risk originated from important reductions in cropping intensity and changes in crop mix rather than from changes in the yields of individual crops. Changes in cropping intensity and crop mix were explained by the combination of reductions in the number of sowing opportunities around critical times in the cropping calendar, and to operational constraints at the whole farm level i.e. limited work capacity in an environment having fewer and more concentrated sowing opportunities. This indicates that indirect impacts from shifts in climate on farm operations can be more important than direct impacts from climate on the yield of individual crops. The results suggest that due to the complexity of farm businesses, impact assessments and opportunities for adaptation to climate change might also need to be pursued at higher integration levels than the crop or the field. We conclude that plasticity can be a desirable characteristic in farming systems operating in highly variable environments, and that integrated whole farm systems analyses of impacts and adaptation to climate change are required to identify important interactions between farm management decision rules, availability of resources, and farmer's preference.     

大豆高世代品系再选择方法的探讨

对两个大豆高世代品系进行再选择。研究了几个主要性状的遗传变异和选择潜力,探讨了性状再选择的可能性。分析了两个品系中８个性状和３个产量性状的综合遗传变异度。在一定选择压下同时进行多性状选择的遗传进状选择的遗传进展进行估计,应用多元正态分布函数的近似计算,估计了多性状综合选择时所需基础群体的规模。为作物育种中多性状遗传进度及群体规模估计提出了新的设想。结果表明,南农８８－４８在６００－１０００株供选群     

Erratum to: Feeding preferences of the Asian elephant (Elephas maximus) in Nepal

Background

The relationships between group size, survival, and longevity vary greatly among social species. Depending on demographic and ecological circumstances, there are both positive and negative effects of group size variation on individual survival and longevity. For socially foraging species in particular there may be an optimal group size that predicts maximum individual survival that is directly related to the potential for information transfer, social coordination, and costs of conspecific interference. Our aim was to investigate this central aspect of evolutionary ecology by focusing on a socially foraging bat, Molossus molossus. This species optimizes foraging success by eavesdropping on the echolocation calls of group members to locate ephemeral food patches. We expected to find the highest survival and longest lifespans in small groups as a consequence of a trade-off between benefits of information transfer on ephemeral resources and costs of conspecific interference.

Results

In a mark-recapture study of 14 mixed-sex M. molossus social groups in Gamboa, Panama, spanning several years we found the expected relatively small and intermediate, but stable groups, with a mean size of 9.6 ± 6.7 adults and juveniles. We estimated survival proxies using Cox proportional hazard models and multistate-mark recapture models generated with recapture data as well as automated monitoring of roost entrances in a subset of the groups. Median survival of females was very short with 1.8 years and a maximum estimated longevity of 5.6 years. Contrary to our expectations, we found no relationship between variation in group size and survival, a result similar to few other studies.

Conclusions

Strong selection towards small group size may result from psychoacoustic and cognitive constraints related to acoustic interference in social foraging and the complexity of coordinated flight. The short lifespans were unexpected and may result from life at the energetic edge due to a highly specialized diet. The absence of a relationship between group size and survival may reflect a similar but optimized survival within the selected range of group sizes. We expect the pattern of small group sizes will be consistent in future research on species dependent on social information transfer about ephemeral resources.

     

Branch development responses to planting density and yield stability in soybean cultivars

The objective of this study was to elucidate variability among soybean cultivars in yield response at different planting densities in reference to branch development. We investigated the main stem and branch seed yield and the branching characteristics of determinate Hokkaido and indeterminate US cultivars at the Rakuno Gakuen University in Ebetsu. In 2009 and 2010, two Japanese and two US cultivars were grown at three densities from 9.5 to 20 plants m^?2. In 2011 and 2012, three cultivars from each region were cultivated at three densities from 8.3 to 22.2 plants m^?2. The seed yields of the US cultivars at densities of 16.7 plants m^?2 or less were markedly higher than those of the Hokkaido cultivars, showing that their yield is less sensitive to lower planting density than Hokkaido cultivars. The difference in yield in response to planting density among cultivars was closely associated with a larger increase in branch seed yield with lower planting density, which effectively compensated for the decrease in main stem number per unit land area. The variability of branch development in response to planting density (branching plasticity) was quantified by correlating branch performance with plant spacing (land area per plant). Some US cultivars exhibited greater branching plasticity than Japanese cultivars with similar growth duration. Results of this study suggest soybean cultivar differs in responsiveness to varied planting density through different branching plasticity.     

A crop model component simulating N partitioning during seed filling in pea

Seed N concentration is one of the main quality parameters in grain legume crops. Since few studies have aimed at modelling both seed and vegetative parts N concentrations, our objective was to model N partitioning between vegetative parts and filling seeds for pea (Pisum sativum L.) in field situations where both N nutrition and the plant genotype varied. A crop model component predicting the time courses of vegetative and seed N concentrations was built using knowledge concerning N partitioning during the seed filling period, which include a previously demonstrated relationship between the rate of individual seed N accumulation and the N availability within plants. A greenhouse experiment where assimilate availability was non-limiting was conducted with two genotypes. This experiment demonstrated the genotypic variability of one of the crop model component parameters, the maximum rate of individual seed N accumulation (SNR_max), allowing introduction of this parameter in the crop model component for the studied genotypes. Field experiments spanning 3 years and comprising various crop N nutrition and four genotypes were conducted to evaluate the crop model component. Observed seed and vegetative parts N concentrations ranged at harvest from 19.3 to 39.1 mg g⁻¹ and from 3.6 to 18.4 mg g⁻¹, respectively. N partitioning was well-simulated by the crop model component except when crops had deficient N nutrition. These results suggest that the parameter “NC_n-remob” (proportion of N in vegetative parts which is not available for remobilization to filling seeds), which is taken as constant in the crop model component, could depend upon the crop nutrition level. A sensitivity analysis highlights the need for a precise calibration of the parameters “NC_n-remob” and “SNR_max”. When the crop N nutrition level and further genotypic variability of these parameters are incorporated in the proposed crop model component, it will become a useful part of a pea crop model predicting yield and seed N concentration.     

Estimation of genetic parameters for characters related to potato propagation by true seed (TPS) in an andigena population

Genetic variances were estimated for a population ofSolarium tuberosum L. subsp.andigena, selected for adaptation to north temperate climatic conditions. Estimates for 15 traits, including some unique to true seed (TPS) propagation, were obtained from trials conducted under short day conditions in Peru. Only non-additive variance was found for yield, but heritability estimates were relatively high for tuber number and tuber size. The results indicated that yield could be increased through selection utilizing additive variance for the component traits, especially tuber size. Estimates of genetic variability for tuber uniformity were low. TPS yield was positively correlated with most other traits except tuber number.     

Cost of resistance to trematodes in freshwater snail populations with low clonal diversity

Background

The persistence of high genetic variability in natural populations garners considerable interest among ecologists and evolutionary biologists. One proposed hypothesis for the maintenance of high levels of genetic diversity relies on frequency-dependent selection imposed by parasites on host populations (Red Queen hypothesis). A complementary hypothesis suggests that a trade-off between fitness costs associated with tolerance to stress factors and fitness costs associated with resistance to parasites is responsible for the maintenance of host genetic diversity.

Results

The present study investigated whether host resistance to parasites is traded off with tolerance to environmental stress factors (high/low temperatures, high salinity), by comparing populations of the freshwater snail Melanoides tuberculata with low vs. high clonal diversity. Since polyclonal populations were found to be more parasitized than populations with low clonal diversity, we expected them to be tolerant to environmental stress factors. We found that clonal diversity explained most of the variation in snail survival under high temperature, thereby suggesting that tolerance to high temperatures of clonally diverse populations is higher than that of populations with low clonal diversity.

Conclusions

Our results suggest that resistance to parasites may come at a cost of reduced tolerance to certain environmental stress factors.

     

Yield stability of induced-early-maturing mutants of mungbean (Vigna radiata) and their use in a multiple-cropping system

The performance of seven mutants of mungbean along with parental types was studied at 41 different sites in three summer crop seasons from 1980 to 1982. The performance of mutants was also studied in spring in the fallow period preceding cotton, and in early summer in the fallow period between wheat harvest and rice/maize planting, to assess their suitability of growing as a catch-crop in these fallows.

The mutants yielded significantly higher and matured 2–4 weeks earlier than parental types, leaving sufficient time to sow the succeeding crops. The mutants were characteristically short-statured, and superior to their parents with respect to number of pods per plant, seed weight, harvest index and productivity per day, but similar in numbers of seeds per pod and seed protein content.

The stability of yield was estimated through regression analysis. Significant genotypic differences were observed among mutants and varieties. Some mutants were widely adapted whereas others performed better in favourable environments. The parental types tended to respond well under poor environments.

Owing to their higher yield potential, early and uniform maturity, and wide adaptability, four mutants were approved as commercial varieties in 1986. These mutants yield 30–50% higher than the parents, mature in 55–70 days, and are suited to both summer and spring crop seasons. Of these four mutants, two can be grown in the fallow period between wheat harvest and rice/maize planting. Because of their determinate plant type, non-shattering pod and top fruit-bearing habit, these mutants are also amenable to intercropping practices and mechanised harvesting operations.

The role of induced mutations for the improvement of mungbean is discussed.     

Optimisation of sample size for the detection of latent infection byRalstonia solanacearum in potato seed tubers in the highlands of Peru

Summary A sampling strategy was evaluated in the Andean highlands of Peru to optimise the detection ofRalstonia solanacearum in seed tubers harvested from symptomless crops. A sensitive and specific serological method developed at CIP was used to detect the pathogen in latently infected tubers. Optimum sample size was evaluated for symptomless crops after analysing various numbers of composite samples and using a binomial distribution model to calculate the detection probabilities.R. solanacearum was detected in all lots from fields with visible symptoms, so validating the detection technique. About half of the seed lots from apparently healthy fields at altitudes of up to 3,100 m were found positive for the pathogen.R. solanacearum was detected with 99% probability in samples of 350 tubers from seed lots from symptomless crops. This number of seed tubers could feasibly be processed in a seed-health test without incurring too high a cost for labour and materials.