Phenotypic Characterization of 16 Accessions of Sunn Hemp in Florida

Abstract

Adoption of sunn hemp (Crotalaria juncea L.) as a cover crop has been limited primarily due to the availability of seed sources, leading to high seed costs and unreliable supplies. Seed production in Florida with the commercially available sunn hemp cultivar Tropic Sun has been largely unsuccessful. An experiment was designed to evaluate 16 accessions of sunn hemp for potential commercial seed production in Florida at three planting dates (May, June, July). Vegetative and reproductive characteristics were evaluated to provide baseline information for future development of a cultivar of sunn hemp that could produce seed in Florida with desirable cover crop attributes. The results indicate that the sunn hemp accessions could be separated into two groups. Regardless of planting date, accessions in Group 1 (PI 234771, PI 248491, PI 295851, PI 337080, PI 468956, PI 561720, PI 652939) displayed desirable cover crop characteristics, such as high biomass production and leaf area. Accessions in Group 1 had a short‐day flowering response and produced few to no pods and seeds. Group 2 accessions (PI 207657, PI 250485, PI 250486, PI 250487, PI 314239, PI 322377, PI 346297, PI 391567, PI 426626) were less sensitive to photoperiod, were generally smaller plants because of earlier transition to reproductive growth, and produced more seedpods and seeds. Seed production was generally better when seeds were sown at the earliest date. It appears that in Florida, sunn hemp accessions that are capable of flowering in summer rather than fall have greater potential for seed production.Core Ideas Based on vegetative and reproductive characteristics sunn hemp accessions could be divided into two groups. Group 1 accessions produce more shoot biomass and have a short‐day flowering response. Flowering occurs in fall when effective pollinators are absent. Group 2 accessions are less sensitive to photoperiod. Group 2 accessions flower in summer when effective pollinators occur and successfully set seed.

Establishment techniques affect productivity, nutritive value and atmospheric N2 fixation of two sunn hemp cultivars

“…Even though crescent sun had significantly lower CP and IVDOM concentrations than blue leaf, both cultivars can still be regarded for their high nutritive value, which compares to the mean values of tropical legumes (Minson, 1990; Poppi & McLennan, 1995). Sunn hemp accessions tend to be diverse in terms of flowering responses and photoperiod sensitivity, which ultimately has an effect on biomass, leaf area and seed production (Cho et al, 2016). Further studies are required to characterize physiological, as well as the morphological differences in crescent sun and blue leaf, as there is a paucity of literature on these cultivars.…”

“…In recent years, however, several sunn hemp cultivars have been released throughout the world, which have also adapted to a wide range of soil types and appear to persist under sandy soils, growing best on well‐drained soils with pH from 5 to 7.5 (USDA, 1999). “Tropic Sun” has historically been the focus of commercial seed production in the continental United States (Abdul‐baki et al, 2001; Cho et al, 2016; USDA, 1983). More recently, “Blue Leaf” and “Crescent Sun” have been released in the commercial market.…”

“…There is, however, a paucity of literature regarding the agronomic characteristics of these two cultivars, especially when it comes to adequate seeding rates and whether or not seed requires inoculation. It is critical to understand the vegetative and reproductive characteristics of these plants, especially since differences exist among accessions of sunn hemp in terms of flowering responses and photoperiod sensitivity, which can affect biomass productivity (Cho et al, 2016).…”

DIVA-GIS based insight into geographical distribution and diversity spectrum of Indian sunnhemp (Crotalaria juncea L.) accessions suitable for diversified applications

“…The limited seed supply is primarily attributed to photoperiod sensitivity of the crop as it flowers only under short day conditions (White and Haun, 1965). Further, the crop reported to be a self-incompatible and cross-pollination is the preferred mode of reproduction, only large bees from the Xylocopa or Megachile genera are capable of effecting pollination (Cho et al, 2016;Hall and Avila, 2016;Thimmaiah et al, 2018). Therefore, seed yield in sunnhemp is mainly depends on two things; availability of the bee population in the locality (Free, 1993) and number of flowers per plant.…”

“…Therefore, seed yield in sunnhemp is mainly depends on two things; availability of the bee population in the locality (Free, 1993) and number of flowers per plant. The first component is largely depends on environment, while the second factor is determined by the genetic potential of the genotype where breeding interventions can be made (Abdul-baki et al, 2001;Cho et al, 2016). Genotypes which can produce more number of branches and bear more number of flowers have a favorable effect on seed yield.…”