Mix and manage: Cultivar mixtures can maintain yield under high wheat blast disease pressure.

Originating in South America, wheat blast disease has spread to both Asia and Africa and is considered a significant threat to food security. Bangladesh experienced the first outbreak of wheat blast outside of the Americas in 2016. Shortly thereafter, the blast-resistant variety BARI Gom 33 was released. Seeds of this variety are however not as widely available as required, although the disease threat remains. While varietal mixtures have been shown to mitigate some symptoms and yield losses associated with other fungal diseases in wheat, there is a complete research gap on this topic as it pertains to wheat blast. As such, we evaluated the potential of using BARI Gom 33 as a component of a variety mixture under high disease pressure in Bangladesh. During three cropping seasons, blast symptoms and yield were determined in a field experiment for the highly blast-susceptible variety BARI Gom 26, the moderately susceptible BARI Gom 30, the resistant BARI Gom 33, and seven mixture combinations of the three varieties using artificial inoculation to increase disease pressure. In addition to wheat blast, Bipolaris leaf blight (BpLB) symptoms were observed and evaluated. While yields of the susceptible varieties were severely affected by blast even after fungicide application, disease-inflicted yield loss without fungicide was only 15% for sole BARI Gom 33 and did not differ significantly from yield losses in BARI Gom 33 and BARI Gom 30 mixtures. Furthermore, in the mixture containing 67% BARI Gom 33 and 33% BARI Gom 30, blast incidence and severity were reduced by 25% and 16%, respectively, in comparison to weighted values in sole stands. Conversely, mixing varieties tended to increase the symptoms of BpLB. Under high wheat blast pressure, fungicide protection against blast was relatively weak, underscoring the importance of resistant varieties. Although variety mixtures did not increase yield, the yield advantage of BARI Gom 33 was maintained when its seeds were mixed with the less resistant BARI Gom 30. This study confirms recommendations that farmers should use BARI Gom 33 as a first line of defense against wheat blast in Bangladesh. Yet where farmers cannot access sufficient BARI Gom 33 seed for planting, our data suggest that agricultural extension services can recommend this variety with non-resistant cultivars as interim strategy without significant risk of yield loss.

A prospective, interventional study comparing the outcomes of macular hole surgery in eyes randomized to C3F8, C2F6, or SF6 gas tamponade.

PURPOSE: Analysis of outcomes of macular hole (MH) surgery using 12% C3F8, 16% C2F6, or 18% SF6 as randomized gas tamponading agent. METHODS: This is a prospective, randomized, interventional study of 159 eyes with idiopathic MH undergoing 23/25G pars-plana vitrectomy with internal limiting membrane peeling and gas tamponade. Eyes were stratified into two groups: Group I (MH < 800 µ) and group II (MH > 800 µ) according to MH apical diameter. Eyes in group I were randomized to receive either 18% SF6, 16% C2F6, or 12% C3F8. Eyes in group II were randomized to either 16% C2F6 or 12% C3F8. Clinical details, MH parameters on optical coherence tomography, surgical details and complications were analyzed. Outcome measures were type of hole closure (I/II), best corrected visual acuity, intraocular pressure, and cataract progression. RESULTS: In Group I (n = 139), type 1 closure was achieved in 107 (77%) eyes. Type 1 closure rates in group I per gas tamponade were as follows: SF6 (70%), C2F6 (80%), C3F8 (78%) (p = 0.503, chi-square test for independence). There was no statistical difference in MH closure rates between SF6 and C2F6 (p = 0.134), SF6 and C3F8 (p = 0.186), and C2F6 and C3F8 (p = 0.373). In Group II (n = 20), type 1 closure was achieved in 12 (60%) eyes. Type 1 closure rates in group II per gas tamponade were as follows: C2F6 (75%), C3F8 (50%) (p = 0.132, Two proportion Z test). Mean follow-up after surgery was 2.66 ± 2.74 months. CONCLUSION: Given the similar outcomes of using 18% SF6, 16% C2F6, or 12% C3F8 in idiopathic macular hole surgery, the advantage of using a shorter acting tamponade translates into earlier recovery and rehabilitation.

Association Mapping of Seedling Resistance to Tan Spot (Pyrenophora tritici-repentis Race 1) in CIMMYT and South Asian Wheat Germplasm.

Tan spot caused by Pyrenophora tritici-repentis (Ptr) is an important disease of wheat in many wheat producing areas of the world. A genome wide association study (GWAS) was conducted using 11,401 SNP markers of the Illumina Infinium 15K Bead Chip with whole genome coverage to identify genomic regions associated with resistance to tan spot in a diverse panel of 184 wheat genotypes originating from South Asia and CIMMYT. The GWAS panel was phenotyped for seedling resistance to tan spot with Ptr race 1 in two greenhouse experiments. Besides CIMMYT germplasm, several lines from South Asia (India, Bangladesh and Nepal) showed good degree of resistance to tan spot. Association mapping was conducted separately for individual experiments and for pooled data using mixed linear model (MLM) and Fixed and random model Circulating Probability Unification (FarmCPU) model; no significant MTAs were recorded through the MLM model, whereas FarmCPU model reported nine significant MTAs located on chromosomes 1B, 2A, 2B, 3B, 4A, 5A, 5B, 6A, and 7D. The long arms of chromosomes 5A and 5B were consistent across both environments, in which the Vrn-A1 locus was found in identified region of chromosome 5A, and MTA at IACX9261 on 5BL appears to represent the resistance gene tsn 1. MTAs observed on chromosomes 1B, 2A, 2B, 3B, 4A, 6A, and 7D have not been reported previously and are likely novel.