*E-mail: rkrishnaroy666@gmail.com (corresponding author- Roy)

The emerging wheat blast disease caused by the fungus Magnaporthe oryzae pathotype Triticum (MoT) is becoming a serious constraint to global wheat production. The disease was initially detected in Brazil in 1985, and later observed in several South American countries as well as in South Asia (2016) and Southern Africa (2018). This emerging and expanding disease urgently needs intensive research on different aspects of pathogen biology to mitigate the threat of wheat blast. Several strategic research activities on wheat blast pathology were undertaken by Bangladesh Wheat and Maize Research Institute (BWMRI) in the last 8 years (2017 to 2024).

These include study of pathogen biology, field survey and monitoring, long-term preservation of isolates, disease epidemiology, fungal virulence, identification of alternative hosts and cross infection, prevalence and survivability of MoT on wheat seeds/straw, infection assays, fungal morphology, molecular identification, and genetic diversity of MoT. Our results show that wheat blast spread from 8 to 29 districts in Bangladesh within the period of 2016 to 2024. To date, around 400 isolates of MoT have been isolated from wheat and other hosts, and all the isolates are preserved in deep freezers. Conditions have been optimized to develop pure cultures of the pathogen, namely: temperature (29oC), light regime (continuous fluorescence light), media (OMA/PDA), and pH (6.5-7.0).

Our study revealed that high temperature (27-29oC) and high humidity (>80%) along with high leaf wetness (>24hrs) is conducive for wheat blast outbreak under field conditions. Several grass weeds (Eleusine, Digitaria, Panicum, Pennisetum etc.) were identified as suspected alternative hosts for the disease. Survival rates on seed and wheat straw were also tested. Survival on wheat seeds was 1.5-2 years and on straw 2-3 months. Seed could serve as sources of infection for future seasons.

Regarding seed to seedling transmission, MoT can move from the coleoptiles, or even sometimes from the secondary roots to the first leaves. Cross infection studies demonstrated that MoT can infect some other cereal crops (durum, triticale, barley, and oat) and at least two grass species (Eleusine and Pennisetum) under laboratory conditions.

Electron microscopy studies indicated that MoT can infect and colonize the rachis within 72hrs after infection. Morphological and molecular characterization have been completed for around 290 isolates. Morphological and molecular variations among the isolates were observed over space and time. Results from these research activities at BWMRI in Bangladesh have resulted in increased understanding, and subsequent management strategies needed for MoT.