Browsing by Browse by FOR 2020 "300209 Germplasm management"

Citrus is an important export commodity of Bhutan that is now decimated by Citrus Huanglongbing (HLB). The production and use of health tested citrus seedlings have been identified as one of the main HLB management strategies and the starting point for the establishment of a successful citrus orchard. However, the production of Health Tested Citrus Seedlings (HTCS) in Bhutan was confronted with multiple issues leading to an embargo on production since 2016. This portfolio investigated the complex issues that led to an embargo on HTCS production in Bhutan. The main aim of the portfolio was to identify issues and solutions to enable restarting of the HTCS production by engaging the stakeholders in framing workable mechanisms and the future pathways for sustaining the HTCS production. Based on the complexity and system thinking perspectives, a transdisciplinary methodological approach was employed. This included five case studies aimed at understanding the different contexts that influence the HTCS production: Firstly, the Bhutanese agricultural research and policy context deployed documentary analysis where 33 government documents were included for framework analysis. Secondly, the research and innovation system used 110 peer-reviewed articles published in the Bhutanese national journals. Thirdly, the technicalities of the HTCS production and regulatory standards used four technical guidelines or documents followed in four countries (US, Spain, Taiwan and Australia). Fourthly, the perspectives of stakeholders from focus group discussions(16 individuals participated) and individual interviews (14 stakeholders participated). Finally, institution field engagement and observations from four institutes involved in HTCS production are presented.

Our findings from the agricultural research and the policy context suggest the need for synchronisation and harmonisation of intervention programs with the actual needs of the beneficiaries. Policy dialogue, between and among policy makers, researchers, funding agencies, and local institutions were found necessary to enhance the effectiveness and efficiency of the intervention program. Likewise, the Bhutanese HTCS production had several factors (the confirmation of disease-free status, adaptation of process, use of tolerant varieties, certification of nursery trees) in deficit which were due to inadequate funds and human resource capacity. Stakeholders' perspective analysis also suggested inadequate fund, human resource capacity and infrastructure. The Bhutanese Department of Agriculture has limited authority and access to communication over the issues identified with the relevant authorities. There is a need for a direct policy dialogue between the relevant agencies to sustain HTCS production in the future.

Barley yellow dwarf (BYD) is a major virus disease which dramatically re-duces wheat yield. Introducing BYD resistance genes into commercial va-rieties has been proven to be effective in reducing damage caused by barley yellow dwarf virus (BYDV). However, only one major resistance gene is readily deployable for breeding; Bdv2 derived from Thinopyrum intermedium is deployed as a chromosomal translocation. In this study, a double haploid (DH) population was developed from a cross between XuBYDV (introduced from China showing very good resistance to BYD) and H-120 (a BYD-sensitive Chinese accession), and was used to identify QTL for BYD resistance. The population was genotyped using an Infinium iSelect bead chip array targeting 90K gene-based SNPs. The disease resistance of DH lines inoculated with BYDV was assessed at the heading stage. The infections were assessed by tissue blot immunoassay (TBIA). Three new QTL were identified on chromosomes 5A, 6A, and 7A for both symptom and TBIA, with all three resistance alleles being inherited from XuBYDV. Some DH lines with the resistance alleles from all three QTL showed high level resistance to BYD. These new QTL will be useful in breeding programs for pyramiding BYD resistance genes.

A reliable method was developed to screen cereal crops for BYDV-PAV resistance in glasshouse experiments. This also entailed the evaluation of traits associated with Barley yellow dwarf virus (BYDV) infection such as leaf discolouration, reduction in growth, biomass and yield traits, and percentage of virus-infected plants, using enzyme-linked immunosorbent assay (ELISA) and tissue blot immunoassay (TBIA). Four glasshouse experiments were conducted with eight wheat, barley and oat varieties inoculated with BYDV-PAV at the 2-leaf stage, using different numbers of viruliferous aphids and different inoculation periods and temperatures. Inoculation with 5–10 viruliferous aphids per plant for 4 days led to a high percentage of infection in susceptible varieties, indicating that this is an effective BYDV screening method when selecting for resistance in cereal crops. For barley and oat, visual evaluation of symptoms is considered adequate for assessing BYDV resistance. However, for wheat it is necessary to evaluate BYDV resistance by ELISA/TBIA tests and plant biomass (at early stage) and grain number and yield (at late stage) measurements.