Detection and characterization of fungus (Magnaporthe oryzae pathotype Triticum) causing wheat blast disease on rain-fed grown wheat (Triticum aestivum L.) in Zambia

Abstract

Wheat blast caused by Magnaporthe oryzae pathotype Triticum (MoT) is a threat to wheat production especially in the warmer-humid environments. In Zambia, wheat blast symptoms were observed for the first time on wheat (Triticum aestivum L.) grown in experimental plots and five farmers' fields in Mpika district of Muchinga Province during the 2017-18 rainy season. Infected plants showed the typical wheat blast symptoms with the spike becoming partially or completely bleached with the blackening of the rachis in a short span of time. Incidence of blast symptoms on nearly all wheat heads was high and ranged from 50 to 100%. Examination of diseased plant leaves showed the presence of elliptical, grayish to tan necrotic lesions with dark borders on the leaf often mixed with other foliar diseases. A study was conducted to isolate and identify the causal pathogen(s) using classical and molecular methods and determine the pathogenicity of the detected disease causal agent. Morphobiometrical determination of causal pathogen revealed conidia with characteristic pear shaped 2-septate hyaline spores associated with M. oryzae species. Preliminary polymerase chain reaction screening of six isolates obtained from wheat blast infected samples with diagnostic primers (MoT3F/R) was conducted at ZARI, Zambia, and subsequent analysis of two isolates with MoT3F/R and C17F/R was performed at USDA-ARS, USA. Both experiments confirmed that MoT is the causal agent of wheat blast in Zambia. Further, pathogenicity tests performed with pure culture isolates from samples WS4 and WS5 produced typical blast symptoms on all the six inoculated wheat genotypes. Results of this study indicate that MoT is causing wheat blast in rain-fed wheat grown in Zambia, thus making it the first report of MoT in Zambia and Africa. This inter-continental movement of the pathogen (disease) has serious implication for wheat production and trade that needs to be urgently addressed.

Screening and Mapping for Head Blast Resistance in a Panel of CIMMYT and South Asian Bread Wheat Germplasm

“…Bread wheat grown in tropical and subtropical regions is subjected to a range of diseases, among which is wheat blast (WB). This is an emerging disease with growing impacts on wheat production in South America, South Asia, and Africa, and is a potential threat to other major wheat producers like India, United States and China ( Duveiller et al, 2016 ; Cruz and Valent, 2017 ; Tembo et al, 2020 ). The disease had been endemic in four South American countries, Brazil, Bolivia, Paraguay, and Argentina, before its outbreak in Bangladesh in 2016, affecting 15,000 ha wheat fields with yield losses of 5–51% ( Islam et al, 2016 ; Malaker et al, 2016 ).…”

“…The disease had been endemic in four South American countries, Brazil, Bolivia, Paraguay, and Argentina, before its outbreak in Bangladesh in 2016, affecting 15,000 ha wheat fields with yield losses of 5–51% ( Islam et al, 2016 ; Malaker et al, 2016 ). Soon thereafter, this disease was identified in the Muchinga Province of Zambia during the 2017–2018 rainy season, indicating its introduction into the African continent ( Tembo et al, 2020 ).…”

A single amino acid polymorphism in a conserved effector of the multihost blast fungus pathogen expands host-target binding spectrum

“…It is possible that shuttling between wild and cultivated plants, as in between E. indica and E. coracana, could have facilitated effector diversification and such cases can serve as a springboards for host range expansions and host-jumps of the blast fungus [67]. This calls for increased surveillance of wild grass hosts, especially in regions affected by emerging blast disease [69][70][71][72], in order to understand the role they play in host-driven adaptation of M. oryzae.…”

Phytosanitary Interventions for Safe Global Germplasm Exchange and the Prevention of Transboundary Pest Spread: The Role of CGIAR Germplasm Health Units

“…Some examples of introduced pests causing epidemics and pandemics with disastrous consequences for food production, livelihoods, and environmental biodiversity include the Irish potato famine in the 1840s caused by Phytophthora infestans, which was introduced from Central America into Ireland [ 11 , 15 ]. Some recent examples of devastating outbreaks caused by transboundary pest introductions into regions where the CGIAR operates include the maize lethal necrosis (MLN) epidemic in East Africa caused by maize chlorotic mottle virus (MCMV), which was introduced from East Asia [ 16 ]; the fall armyworm ( Spodoptera frugiperda ) outbreak in Africa and Asia, caused by the likely introduction of insect pest from the Americas [ 17 ]; the cassava mosaic disease outbreak in East Asia, caused by the Sri Lankan cassava mosaic virus (SLCMV), which was introduced from South Asia [ 18 ]; the banana bunchy top virus (BBTV) outbreak in the sub-region of Western Africa due the spread of the virus through planting material from the sub-region of Central Africa [ 19 ]; the expansion of banana wilt caused by the Fusarium oxysporum Tropical Race 4, which was introduced from Southeast Asia into South (India) and West Asia (Jordon and Israel), Mozambique and Colombia [ 20 ]; the outbreak of potato cyst nematode, Globodera pallida , in Kenya by the likely introduction of the pest from Europe [ 21 ]; the wheat blast outbreak in Bangladesh [ 22 ] and, more recently, in Zambia [ 23 ], caused by the Magnaporthe oryzae pathotype Triticum, introduced from South America; the spread of Candidatus Liberibacter solanacearum haplotype A and its vector, Bactericera cockerelli (potato psyllid), which is responsible for the potato Zebra chip disease and potato purple top disease, which are likely to have spread from the Central American region to Ecuador in South America [ 24 ]. The occurrence of these new pests in the territories was recognized during obvious disease outbreaks.…”