Soybean fruit development and set at the node level under combined photoperiod and radiation conditions

In soybean, long days during post-flowering increase seed number. This positive photoperiodic effect on seed number has been previously associated with increments in the amount of radiation accumulated during the crop cycle because long days extend the duration of the crop cycle. However, evidence of intra-nodal processes independent of the availability of assimilates suggests that photoperiodic effects at the node level might also contribute to pod set. This work aims to identify the main mechanisms responsible for the increase in pod number per node in response to long days; including the dynamics of flowering, pod development, growth and set at the node level. Long days increased pods per node on the main stems, by increasing pods on lateral racemes (usually dominated positions) at some main stem nodes. Long days lengthened the flowering period and thereby increased the number of opened flowers on lateral racemes. The flowering period was prolonged under long days because effective seed filling was delayed on primary racemes (dominant positions). Long days also delayed the development of flowers into pods with filling seeds, delaying the initiation of pod elongation without modifying pod elongation rate. The embryo development matched the external pod length irrespective of the pod's chronological age. These results suggest that long days during post-flowering enhance pod number per node through a relief of the competition between pods of different hierarchy within the node. The photoperiodic effect on the development of dominant pods, delaying their elongation and therefore postponing their active growth, extends flowering and allows pod set at positions that are usually dominated.Facultad de Ciencias Agrarias y Forestale

Studies to elucidate some effects of Cytokinins on the reproductive potential of Vicia Faba L.

Abscission of flowers and loss of pods appear to be part of normal reproductive development in Vicia faba L. The biological processes leading to this loss of reproductive potential are yet to be elucidated, but may be mediated by a lack of an adequate cytokinin supply to the reproductive organs. External application of cytokinins was used in this study to help further understand the regulation of reproductive loss in this species. The effect of six cytokinins on the reproductive potential of broad beans, grown under controlled conditions, was studied by local application of the chemicals on every inflorescence having flowers prior to and at full petal opening. 6-(benzylamino) purine (BA) and 6-[benzylamino-9-(2-tetrahydropyranyl)] purine ([9tP]BA) were the most active compounds in preventing flower abscission, regardless of the flower position on the plant. However, this early increase in reproductive potential was eliminated due to compensatory pod-drop during their development. It was suggested in the discussion that repeated applications of these compounds may prevent abortion of the pods. In field experiments using various cultivars of V. faba L., the reproductive portions of plants were sprayed twice with cytokinins, at early flowering and at early pod-initiation. Both BA-compounds resulted in almost complete flower retention. It was the varieties for all subspecies that normally set fewer pods that showed the better response to cytokinin treatment. The response of subspecies of Vicia faba to cytokinins in descending order was major > equina > minor. At harvest, analysis of the cytokinin effects on yield components indicated a great variation in plants within each variety. Thus, recorded increases in the dry weight of harvestable organs were not statistically different from controls apart from cv. Toret, a uniform variety. Depending on the variety, consistent enhancement in fruit-set in faba bean due to BA-application was associated with increased sucrose synthase activity and/or acid invertase activity at carpels before or at pollination, measured 24h after the application of the growth substance. Subsequently, an investigation of the inter-relationships between sucrose content of the carpel and successful pod-set after application of BA was performed. Each flower was at a known stage of development. The probability of each flower achieving pod-set was also known by virtue of its position on the inflorescence. Treatment with BA 24 hours before anthesis caused all flowers to set a pod, and this was accompanied by an increase in sugar content of the carpel one day after application. Decreases in glucose and fructose content were also found, a few days later, when flower-petals collapsed. These results are fully discussed in relation to sink development in Vicia faba. In conclusion it is suggested that cytokinins strongly influence pod-set in V. faba L. The metabolism of sugar in vivo before or at pollination of the flower appears to be, at least part of the way cytokinin effects its action. To investigate this further, new methodologies need to be developed to elucidate the mode of action of cytokinin on sugar metabolism before or at anthesis of the flower and its relation to successful pod-set

Effect of heat stress on pollen development and seed set in field pea (Pisum sativum L.)

Pea (Pisum sativum L.) is a major legume crop grown in a semi-arid climate in western Canada, where heat stress often causes flower abortion and reduces yield. Heat specifically affects pollination and seed set, the processes associated with pollen fertilizing an ovule to form an embryo, and seed development. The goals of this research were to investigate the effect of heat stress on pollen development, function, and seed set, and to identify single nucleotide polymorphism (SNP) markers associated with reproductive development traits via association mapping. Heat stress reduced pollen viability, the proportion of ovules that received a pollen tube, seed number per pod, and the seed-ovule ratio in a pod when exposed to 35/18°C day/night temperatures for 4-7 days. Heat stress also reduced ovule viability with P = 0.09. High temperature reduced in vitro pollen germination by approximately 30% in CDC Sage and 55% in CDC Golden when the 10-h incubation temperature increased from 24 °C to 36 °C. Pollen wall (intine) thickness increased by 46% from 222 nm to 414 nm as a result of heat stress, and anther dehiscence failed to occur following exposure to 35/18°C day/night for 7 days. The lipid region of the pollen coat and exine of CDC Sage was more stable compared to CDC Golden, which may explain the greater robustness of CDC Sage pollen to elevated temperature. Timing of flower appearance and age of the two flowers is sequential on a nodal raceme, and nodes and flowers along the main stem are also sequential. Heat stress impacted young, barely visible floral buds in the developing inflorescence apex more than more advanced buds and open flowers. The flower abortion rate was greater when plants were exposed to heat stress and when young flower buds were visible at the first reproductive node (T1) compared to the development stage when flowers at the second reproductive node were fully open (T2). Similarly, seed-set, pod development, and seed yield were more negatively affected when high temperature exposure started at T1 compared to T2. Seed development was negatively impacted by the pollen interaction with pistil under heat stress, such as anther indehiscence and fewer ovules evidently fertilized. Heat stress accelerated seed abortion in all ovule positions within pods. In half of the cultivars tested, ovules at the pod’s medial and stylar-end positions were more likely to develop into seeds compared to basal ovules. Cultivars with small seed-size such as ‘40-10’ and ‘Naparnyk’ were able to retain the most ovules and seeds per pod compared to large seed size cultivars, and large-seeded cultivars like ‘MFR043’ aborted seeds when exposed to heat. Population structure analysis was conducted on a panel of 92 diverse pea varieties, and they clustered into three subpopulations mainly consistent with their geographical origins. Association analyses identified 60 single nucleotide polymorphisms (SNPs) significantly associated with reproductive development related traits including days to flowering (DTF), duration of flowering (DOF), number of reproductive nodes, number of pods on the main stem, pod set potential, percentage of pod set, and pollen germination reduction due to heat stress. Among these 60 marker-trait associations, 33 SNPs were associated with the onset of flowering, 8 SNPs with pod development, and 19 SNPs with the number of reproductive nodes. Twelve SNPs associated with DTF and 2 SNPs associated with DOF overlapped with the SNP markers associated with the number of reproductive nodes. However, markers associated with in vitro pollen germination were not found due to the variability in sampling 92 genotypes. The findings obtained from this research will benefit plant physiologists and plant breeders for a better understanding of successful reproductive development in field pea and other legume crops experiencing increasing temperatures due to global climate change

Yield Components and Biomass Partition in Soybean: Climate Change Vision

Long-term climate change and inter-annual climate variability are events of concern to farmers and humanity. Global warming could affect agriculture in various ways and it is anticipated that agricultural systems will face great pressure from the variability of climate factors and their extreme events, which in most cases are difficult to predict, particularly extreme events of rainfall, higher dry season, hot and cold waves and their interactions. Global warming could also have some positive effects for plants such as increasing the temperature of current cold regions and increasing carbon dioxide with its positive effect on photosynthesis, growth rates, the use of water and production. Meanwhile, there are still many questions that remain about this possible future. This chapter, brings the response of plants to future conditions through specifics alterations in its components of yield on environmental conditions with enrichment of CO2 and elevated temperature, two climatic factors, which is understood to be the factors of climatic change of greater global extent. The study of the components of yield and their alterations, can guide diverse sectors of the sciences and decision makers, in order to structure strategies of resilience in the cultivation of soybean

Genetic and environmental effects on crop development determining adaptation and yield

Slafer, Gustavo Ariel. ICREA - AGROTECNIO - Spain.Kantolic, Adriana Graciela. Universidad de Buenos Aires. Facultad de Agronomía. Buenos Aires, Argentina.Appendino, María Laura. Universidad de Buenos Aires. Facultad de Agronomía. Buenos Aires, Argentina.Tranquilli, Gabriela Edith. Instituto Nacional de Tecnología Agropecuaria (INTA). Recursos Naturales. Instituto de Recursos Biológicos. Buenos Aires, Argentina.Miralles, Daniel Julio. Universidad de Buenos Aires. Facultad de Agronomía. Buenos Aires, Argentina.Savin, Roxana. ICREA - AGROTECNIO - Spain.Crop development is a sequence of phenological events controlled by the genetic background and influenced by external factors, which determines changes in the morphology and/or function of organs (Landsberg, 1977). Although development is a continuous process, the ontogeny of a crop is frequently divided into discrete periods, for instance ‘vegetative’, ‘reproductive’ and ‘grain - filling’ phases (Slafer, 2012). Patterns of phenological development largely determine the adaptation of a crop to a certain range of environments. For example, genetic improvement in grain yield of wheat has been associated with shorter time from sowing to anthesis in Mediterranean environments of western Australia (Siddique et al., 1989), whereas no consistent trends in phenology were found where drought is present but not necessarily terminal, including environments of Argentina, Canada and the USA (Slafer and Andrade, 1989, 1993; Slafer et al., 1994a) (Fig. 12.1). Even in agricultural lands of the Mediterranean Basin where wheat has been grown for many centuries, breeding during the last century did not clearly change phenological patterns (Acreche et al., 2008). This chapter focuses on two major morphologically and hysiologically contrasting grain crops: wheat and soybean. For both species, we have an advanced understanding of development and physiology in general. Wheat is a determinate, long-day grass of temperate origin, which is responsive to vernalization. Soybean is a typically indeterminate (but with determinate intermediate variants), short-day grain legume of tropical origin, which is insensitive to vernalization. Comparisons with other species are used to highlight the similarities and differences. The aims of this chapter are to outline the developmental characteristics of grain crops and the links between phenology and yield, to revise the mechanisms of environmental and genetic control of development and to explore the possibilities of improving crop adaptation and yield potential through the fine-tuning of developmental patterns

Effects of Cultural Practices on Soybean Nectar Production

Experiments were conducted to determine the effects of cultural practices such as irrigation, planting date, and maturity group on soybean nectar production. Multiple interactions between different factors influences the amount of total sugar present in soybean flowers. Pod production was increased in later planted soybean, but later planting resulted in reduction in yield. Another study was conducted to explore the effects that variety selection had on soybean nectar production. Soybean nectar production was highly variable among varieties and was influenced further depending on their growing location. Later maturing varieties produced significantly more soybean pods. This increase in pod production was not reflected in yield, as the later maturing varieties usually yielded less

Analysis of agromorphological diversity of southern Tunisia faba bean (Vicia faba L.) germplasm

Forty two faba bean landraces (traditional farmers’ varieties) (Vicia faba L.) from southern Tunisia, belonging to 8 oasis agro-ecosystems were assessed using morphological descriptors. The studied descriptors focused on morpho-phenological and morpho-agronomical traits. The data obtained is extracted on the basis of 35 descriptors of 42 populations from 8 localities, at a rate of 30 replications (plants) per population, in totality of 1260 individuals. The data underwent an analysis of variance and a multivariate analysis. Significant differences among populations for the thirty five descriptors were observed. The multivariate analysis performed on averages of all parameters revealed eight main groups, and variation within the same oasis agro-ecosystems was extremely important. Particularly, the group of ‘Tozeur’ made up of five populations (P38, P39, P40, P41 and P42), and the group of ‘Medenine’ composed of seven populations (P19, P20, P21, P22, P23, P24 and P25) showed a special characters than the other populations especially for seedling characters. The geographical location did not seem to be the main factor structuring the variability of the studied landraces. There proved to be substantial phenotypic variability in the Tunisian faba bean germplasm.Keywords: Diversity analysis, germplasm, faba bean (Vicia faba L.), oasis agro-ecosystems, Southern Tunisi