Nodulation and root growth increase in lower soil layers of water‐limited faba bean intercropped with wheat

Below‐ground niche complementarity in legume–cereal intercrops may improve resource use efficiency and root adaptability to environmental constraints. However, the effect of water limitation on legume rooting and nodulation patterns in intercropping is poorly understood. To advance our knowledge of mechanisms involved in water‐limitation response, faba bean (Vicia faba L.) and wheat (Triticum aestivum L.) were grown as mono‐ and intercrops in soil‐filled plexiglass rhizoboxes under water sufficiency (80% of water‐holding capacity) and water limitation (30% of water‐holding capacity). We examined whether intercropping facilitates below‐ground niche complementarity under water limitation via interspecific root stratification coupled with modified nodulation patterns. While no significant treatment effects were measured in intercropped wheat growth parameters, water limitation induced a decrease in shoot and root biomass of monocropped wheat. Likewise, shoot biomass and height, and root length of monocropped faba bean significantly decreased under water limitation. Conversely, water limitation stimulated root biomass of intercropped faba bean in the lower soil layer (15–30 cm soil depth). Similarly, total nodule number of faba bean roots as well as nodule number in the lower soil layer increased under intercropping regardless of water availability. Under water limitation, intercropping also led to a significant increased nodule biomass (48%) in the lower soil layer as compared to monocropping. The enhanced nodulation in the lower soil layer and the associated increase in root and shoot growth provides evidence for a shift in niche occupancy when intercropped with wheat, which improves water‐limited faba bean performance.     

Chitosan as a wall material for a microencapsulated delivery system for Macrobrachium rosenbergii (de Man) larvae

Chitosan has been widely accepted as a wall material for preparing microcapsules of various purposes in human medicine. The possibility of using chitosan as a wall material for microencapsulating nutrients and drugs for aquaculture purposes, specifically to Macrobrachium rosenbergii larvae was evaluated in this study. Two types of chitosan-coated microcapsules were prepared using either acetone (MEC-A) or NaOH (MEC-N) as the cross-linking agents. They were compared with a microbound diet relative to total leaching of nutrients and free amino acids (FAA). Among the microcapsules, MEC-N showed the lowest level of total leaching of nutrients (23.3%) during 5 h of immersion in seawater and released 65% FAA after 60 min. During laboratory trials, 75% larvae had accepted the MEC-N capsule. The results of the study suggest that chitosan can be used as a wall material for preparing microcapsules to deliver drugs and nutrients to M. rosenbergii larvae.     

Mapping QTLs using a novel source of salinity tolerance from Hasawi and their interaction with environments in rice

Background

Salinity is one of the most severe and widespread abiotic stresses that affect rice production. The identification of major-effect quantitative trait loci (QTLs) for traits related to salinity tolerance and understanding of QTL × environment interactions (QEIs) can help in more precise and faster development of salinity-tolerant rice varieties through marker-assisted breeding. Recombinant inbred lines (RILs) derived from IR29/Hasawi (a novel source of salinity) were screened for salinity tolerance in the IRRI phytotron in the Philippines (E1) and in two other diverse environments in Senegal (E2) and Tanzania (E3). QTLs were mapped for traits related to salinity tolerance at the seedling stage.

Results

The RILs were genotyped using 194 polymorphic SNPs (single nucleotide polymorphisms). After removing segregation distortion markers (SDM), a total of 145 and 135 SNPs were used to construct a genetic linkage map with a length of 1655 and 1662 cM, with an average marker density of 11.4 cM in E1 and 12.3 cM in E2 and E3, respectively. A total of 34 QTLs were identified on 10 chromosomes for five traits using ICIM-ADD and segregation distortion locus (SDL) mapping (IM-ADD) under salinity stress across environments. Eight major genomic regions on chromosome 1 between 170 and 175 cM (qSES1.3, qSES1.4, qSL1.2, qSL1.3, qRL1.1, qRL1.2, qFWsht1.2, qDWsht1.2), chromosome 4 at 32 cM (qSES4.1, qFWsht4.2, qDWsht4.2), chromosome 6 at 115 cM (qFWsht6.1, qDWsht6.1), chromosome 8 at 105 cM (qFWsht8.1, qDWsht8.1), and chromosome 12 at 78 cM (qFWsht12.1, qDWsht12.1) have co-localized QTLs for the multiple traits that might be governing seedling stage salinity tolerance through multiple traits in different phenotyping environments, thus suggesting these as hot spots for tolerance of salinity. Forty-nine and 30 significant pair-wise epistatic interactions were detected between QTL-linked and QTL-unlinked regions using single-environment and multi-environment analyses.

Conclusions

The identification of genomic regions for salinity tolerance in the RILs showed that Hasawi possesses alleles that are novel for salinity tolerance. The common regions for the multiple QTLs across environments as co-localized regions on chromosomes 1, 4, 6, 8, and 12 could be due to linkage or pleiotropic effect, which might be helpful for multiple QTL introgression for marker-assisted breeding programs to improve the salinity tolerance of adaptive and popular but otherwise salinity-sensitive rice varieties.

     

Causes and feedbacks to widespread grass invasion into chaparral shrub dominated landscapes

Landscape Ecology - This study provides a unified, holistic framework for predicting the dynamics of shrub-grass conversion throughout Mediterranean-climate shrublands. This work focuses...     

Emamectin,a novel insecticide for controlling field crop pests

Emamectin is a macrocyclic lactone insecticide with low toxicity to non-target organisms and the environment, and is considered an important component in pest-management programmes for controlling field crop pests. It is a powerful compound for controlling the cotton bollworm Helicoverpa armigera (Hübner). A spray concentration of 25 mg AI litre-1 in a cotton field resulted in over 90% suppression of H armigera larvae up to day 28 after treatment, while similar mortality of the Egyptian cotton leafworm Spodoptera littoralis Boisduval, under the same conditions, was maintained for 3 days only. Emamectin is a potent compound for controlling the western flower thrips Frankliniella occidentalis (Pergande) under both laboratory and field conditions and its activity on adults was over 10-fold greater than that of abamectin. Spray concentrations of 10 and 50 mg AI litre-1 in Ageratum houstonianum Mill flowers resulted in total suppression of adults up to day 11 and of larvae up to day 20 after treatment. Under standard laboratory conditions, emamectin exhibits a considerable activity on the whitefly Bemisia tabaci (Gennadius) and the leafminer Liriomyza huidobrensis (Blanchard). Further studies are required to evaluate its potential activity on the latter pests under field conditions.     

Assessment of the response of carrot somaclones to Pythium violae, causal agent of cavity spot

Cavity spot is a major disease of carrots, causing cavities on the surface of the root. Available commercial varieties show a range of susceptibility but no significant resistance. Seed progeny from 46 tissue culture-derived carrot ( Daucus carota ) somaclones were screened for viability, then 19 selected somaclone families were sown under glasshouse conditions, along with commercial cultivars (Bertan, Nandor, Bolero and Vita Longa) as controls. Mature roots were exposed to Pythium violae in a cavity spot bioassay to determine their response as measured by disease incidence and severity. Some somaclones formed fewer lesions than the least susceptible control cultivar, Vita Longa. Seven somaclonal families that showed a range of susceptibility were sown under field conditions and the assessment was repeated. Although there was little relationship between glasshouse and field-trial results, under field conditions one of the somaclones had a mean incidence of disease, as estimated by transformed data, of 1·9 compared with 37·9 for the most susceptible somaclone and 3·5 for Bolero, the most resistant commercial cultivar. The results indicated that significant genetic variation in susceptibility to cavity spot disease was present in the somaclones.     

Temporal changes in soil carbon and nitrogen in west African multistrata agroforestry systems: a chronosequence of pools and fluxes

The conversion of forests to agroecosystems or agroforests comes with many changes in biological and chemical processes. Agroforestry, a tree based agroecosystem, has shown promise with respect to enhanced system nutrient accumulation after land conversion as compared to sole cropping systems. Previous research on tropical agroforestry systems has revealed increases in soil organic matter and total organic nitrogen in the short term. However, research is lacking on long-term system level sustainability of nutrient cycles and storage, specifically in traditional multi-strata agroforestry systems, as data on both the scope and duration of nutrient instability are inconclusive and often conflicting. This study, conducted in Ghana, West Africa, focused on carbon and nitrogen dynamics in a twenty-five year chronosequence of cacao (Theobroma cacao Linn.) plantations. Three treatments were selected as on-farm research sites: 2, 15 and 25-year-old plantations. Soil carbon (C, to a depth of 15 cm) varied between treatments (2 years: 22.6 Mg C ha⁻¹; 15 years: 17.6 Mg C ha⁻¹; 25 years: 18.2 Mg C ha⁻¹) with a significant difference between the 2- and 15- and the 2- and 25-year-old treatments (p < 0.05). Total soil nitrogen in the top 15 cm varied between 1.09 and 1.25 Mg N ha⁻¹ but no significant differences were noted between treatments. Soil nitrification rates and litter fall increased significantly with treatment age. However, photosynthetically active radiation (PAR) and soil temperature showed a significant decrease with age. No difference was found between decay rates of litter at each treatment age. By 25 years, system carbon sequestration rates were 3 Mg C ha⁻¹ y⁻¹, although results suggest that even by 15 years, system-level attributes were progressing towards those of a natural system.