Wheat spike blast: genetic interventions for effective management.

The fundamental concepts of the genetics, race classification and epidemiology of the Wheat spike blast causing fungus Magnaporthe oryzae pathotype Triticum (MoT) are still evolving despite of its discovery in 1985 in Brazil for the first time. The fungus seems to defy the research progress that is being made globally by continuously evolving into pathotypes which have already overcome the much celebrated 2NS resistance in wheat lines as well as few of the initially effective fungicides. The compartmentalized i.e. two speed genome of the MoT, conferring the fungus an evolutionary advantage, has emerged as a challenge for the wheat spike blast researchers complicating its already difficult management. The airborne fungus with a range of alternative hosts is finding new geographical niches situated on different continents and is a matter of great apprehension among the nations whose food security is primarily dependent on wheat. The wheat blast outbreak in Bangladesh during 2016 was attributed to an isolate from Latin America escaping through a seed import consignment while the latest Zambian outbreak is still to be studied in detail regarding its origin and entry. The challenges in dealing wheat spike blast are not only on the level of genetics and epidemiology alone but also on the levels of policy making regarding international seed movement and research collaborations. The present review deals with these issues mainly concerning the effective management and controlling the international spread of this deadly disease of wheat, with a particular reference to India. We describe the origin, taxonomy, epidemiology and symptomology of MoT and briefly highlight its impact and management practices from different countries. We also discuss the advances in genomics and genome editing technologies that can be used to develop elite wheat genotypes resistant against different stains of wheat spike blast.

Karnal Bunt: A Re-Emerging Old Foe of Wheat.

Wheat (Triticum aestivum L.) crop health assumes unprecedented significance in being the second most important staple crop of the world. It is host to an array of fungal pathogens attacking the plant at different developmental stages and accrues various degrees of yield losses owing to these. Tilletia indica that causes Karnal bunt (KB) disease in wheat is one such fungal pathogen of high quarantine importance restricting the free global trade of wheat besides the loss of grain yield as well as quality. With global climate change, the disease appears to be shifting from its traditional areas of occurrence with reports of increased vulnerabilities of new areas across the continents. This KB vulnerability of new geographies is of serious concern because once established, the disease is extremely difficult to eradicate and no known instance of its complete eradication using any management strategy has been reported yet. The host resistance to KB is the most successful as well as preferred strategy for its mitigation and control. However, breeding of KB resistant wheat cultivars has proven to be not so easy, and the low success rate owes to the scarcity of resistance sources, extremely laborious and regulated field screening protocols delaying identification/validation of putative resistance sources, and complex quantitative nature of resistance with multiple genes conferring only partial resistance. Moreover, given a lack of comprehensive understanding of the KB disease epidemiology, host-pathogen interaction, and pathogen evolution. Here, in this review, we attempt to summarize the progress made and efforts underway toward a holistic understanding of the disease itself with a specific focus on the host-pathogen interaction between T. indica and wheat as key elements in the development of resistant germplasm. In this context, we emphasize the tools and techniques being utilized in development of KB resistant germplasm by illuminating upon the genetics concerning the host responses to the KB pathogen including a future course. As such, this article could act as a one stop information primer on this economically important and re-emerging old foe threatening to cause devastating impacts on food security and well-being of communities that rely on wheat.

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.