Branch Angle and Leaflet Shape are Associated with Canopy Coverage in Soybean

Early canopy coverage is a desirable trait that promotes faster ground coverage, resulting in reduced soil evaporation, increased light interception, biomass production and weed suppression, all of which are important determinants of yield in soybean (Glycine max). Variation in traits comprising shoot architecture can influence canopy coverage, canopy light interception, canopy-level photosynthesis, and source-sink partitioning efficiency. However, little is known about the extent of phenotypic diversity of shoot architecture traits and their genetic control in soybean. Thus, we sought to understand the contribution of shoot architecture traits to canopy coverage and to determine the genetic control of these traits. We examined the natural variation for shoot architecture traits in a set of 399 diverse maturity group I soybean (SoyMGI) accessions to identify relationships between traits, and to identify loci that are associated with canopy coverage and shoot architecture traits. Canopy coverage was correlated with branch angle, number of branches, plant height and leaf shape. Using previously collected 50K SNP data on the SoyMGI panel, we identified QTL associated with branch angle, number of branches, branch density, leaf length/width ratio, days to flowering, maturity, plant height, number of nodes and stem termination. In many cases QTL intervals overlapped with previously described genes or QTL. Of particular note, we found QTL associated with branch angle and leaflet shape located on chromosomes 19 and 4, respectively, and these QTL overlapped with QTL associated with canopy coverage, suggesting the importance of branch angle and leaflet shape in determining canopy coverage. Taken together, our results highlight the role individual architecture traits play in canopy coverage and contribute information on their genetic control that could help facilitate future efforts in their genetic manipulation.

Quantifying the importance of a realistic tomato (Solanum lycopersicum) leaflet shape for 3-D light modelling

Background and Aims Leaflet shapes of tomato plants (Solanum lycopersicum) have been reduced to simple geometric shapes in previous functional–structural plant models (FSPMs) in order to facilitate measurements and reduce the time required to reconstruct the plant virtually. The level of error that such simplifications introduce remains unaddressed. This study therefore aims to quantify the modelling error associated with simplifying leaflet shapes. Methods Realistic shapes were implemented in a static tomato FSPM based on leaflet scans, and simulation results were compared to simple geometric shapes used in previous tomato FSPMs in terms of light absorption and gross photosynthesis, for both a single plant and a glasshouse scenario. Key Results The effect of simplifying leaflet shapes in FSPMs leads to small but significant differences in light absorption, alterations of canopy light conditions and differences in photosynthesis. The magnitude of these differences depends on both the type of leaflet shape simplification used and the canopy shape and density. Incorporation of realistic shapes requires a small increase in initial measurement and modelling work to establish a shape database and comes at the cost of a slight increase in computation time. Conclusions Our findings indicate that the error associated with leaflet shape simplification is small, but often unpredictable, and is affected by plant structure but also lamp placement, which is often a primary optimization goal of these static models. Assessment of the cost–benefit of realistic shape inclusion shows relatively little drawbacks for a decrease in model uncertainty.

Taxonomic notes on the Rhynchosia densiflora group (Phaseoleae, Fabaceae) in South Africa and its segregation from Rhynchosia section Arcyphyllum

Background: Rhynchosia section Arcyphyllum is one of the five sections of Rhynchosia as currently circumscribed. Previous studies in South Africa placed two species of Rhynchosia in this section. Some authors treated the species as a group rather than a section, to avoid phytogeographical confusion because the section is based on the North American generic name Arcyphyllum.Objectives: To formally remove the South African taxa from section Arcyphyllum and to provide diagnostic features for these taxa, a key to the subspecies, distribution maps and an illustration of their morphological features.Methods: Observations were made on herbarium specimens housed at NH, NU and PRE. Several field trips were undertaken in search of Rhynchosia connata. Morphological and anatomical features were studied and measurements of characters recorded.Results: In South Africa, the section was until now represented by two species, Rhynchosia densiflora (subsp. chrysadenia) and R. connata. These were separated primarily on stem indumentum, stipule shape, petiole length, leaflet shape and apices. However, this study revealed that there are no clear discontinuities between the two taxa apart from the lobes of the uppermost calyx lip, which are connate more than halfway in R. connata and up to halfway in R. densiflora subsp. chrysadenia. Therefore, R. connata is here relegated to varietal level as R. densiflora subsp. chrysadenia var. connata (Baker f.) Jaca Moteetee.Conclusions: Two varieties of Rhynchosia densiflora subsp. chrysadenia occur in South Africa and are treated as part of the R. densiflora group instead of section Arcyphyllum.

REVISITING THE TAXONOMIC DIVERSITY OF GUIBOURTIA IN THE NEOTROPICS (LEGUMINOSAE, DETARIOIDEAE)

Guibourtia is a genus of Leguminosae comprising ca. 15 mostly African species, but it is also represented in the Neotropics, with populations in Cuba and South America. The Neotropical populations have been treated as comprising one to several species and/or infraspecific taxa. To access the distinctiveness of these putative taxa in the Neotropics, we analyzed morphological variation in herbarium specimens. Morphological discontinuities in leaflet shape, texture, and venation, and ovary pubescence support the recognition of two geographically disjunct species: G. hymenaeifolia in Cuba and G. chodatiana in South America. Another taxon, Guibourtia confertiflora is known from only a single specimen from northeastern Brazil. It possess characteristics of both Guibourtia and the related genus Peltogyne, and in most respects, it resembles the sympatric species Peltogyne pauciflora. We tentatively exclude it from our analysis pending further study. We provide an identification key, descriptions and illustrations of all treated taxa, taxonomic comments and formalization of synonyms and lectotypifications.