Genetic control of resistance to rice yellow mottle virus disease in two rice crosses

Rice (Oryza spp; 2n=24.) production in Uganda and Africa in general, is seriously threatened by the Rice yellow mottle virus disease (RYMVD), a disease caused by Rice yellow mottle virus (RYMV) within the genus Sobemovirus; family Sobemoviridae. This study investigated the existence and distribution of resistance-breaking RYMV pathotype in the three major lowland rice catchment areas in Uganda. Four known rice accessions resistant to Rice yellow mottle virus (RYMV) namely; Gigante, Tog5672, Tog5674 and Tog5681, carrying resistant allele’s rymv1-2, rymv1-4 & RYMV3, rymv1-5 and rymv1-3, respectively, were tested for their response to different RYMV isolates. The isolates were collected from three major lowland rice catchment areas of Doho, Kibimba, and Olweny in Uganda. Out of 100 leaf samples collected from the field and assayed for RYMV and confirmed to be positive using RT-PCR, 83 isolates induced symptoms on IR64- the RYMV susceptible line. Seventy-seven (92.8%) isolates were able to overcome resistance in at least one of the four differential rice accessions, as confirmed by the presence of RYMV symptoms; while 6 (7.2%) isolates were asymptomatic. Variation in time (days) for symptom development post-inoculation (dpi) and AUDPC were observed. Symptoms appeared within 5-7 days on IR64; while it took on average 11, 18, 36, and 18 days to appear on Gigante, Tog5672, Tog5674 and Tog5681, respectively. The highest AUDPC was observed on IR64 (254.7); while the lowest was observed on Tog5681 (74.1). Two major patho-groups were observed; those that broke down resistance in Gigante only (25.3%) and Gigante & Tog5672 (33.7%). Five isolates from Doho (Budaka & Bugiri districts) and Kibimba (Butaleja district) catchment areas broke down RYMV resistance in three accessions i.e. (Tog5681, Gigante & Tog5672) and (Tog5674, Gigante & Tog5672), respectively. Resistance breaking isolates were confirmed in all the three sampled catchment zones, however, Doho and Kibimba had some unique isolates that broke down resistance in accessions carrying resistance allele rymv 1-3 and rymv1-5 in addition to rymv1-2. Results from this study showed that RYMV isolates in Uganda can break down resistance conferred by the rymv1-2 resistance gene allele. However, accessions Tog5681 and Tog5674 seem to hold stable RYMV resistance and, thus are recommended for RYMV breeding.

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Incidence and Distribution of Rice Yellow Mottle Virus Disease in Kebbi State, Nigeria

Journal of Agriculture and Ecology Research International ◽

10.9734/jaeri/2019/v20i1-230094 ◽

2019 ◽

pp. 1-7

Author(s):

I. U. Mohammed ◽

Y. A. Busari ◽

A. Muhammad ◽

R. Idris ◽

M. Adamu ◽

...

Keyword(s):

Local Governments ◽

Virus Disease ◽

Hot Spot ◽

Disease Incidence ◽

The State ◽

Mottle Virus ◽

Rice Yellow Mottle Virus ◽

Yellow Mottle ◽

Leaf Deformation ◽

Severity Of The Disease

The study was conducted to assess the incidences of Rice Yellow Mottle Virus disease (RYMVD) in Kebbi State Nigeria, a field survey was conducted in four rice-growing areas of the State. Rice fields were selected randomly at 2 km interval, severity of the disease was assess using arbitrary five-point scale and disease incidence was assessed according to the proportion of the plants showing symptoms. Thirty plants were assessed in each field visited. Symptoms occurred in varying levels of incidence. The presence of RYMV in the collected samples was confirmed using Reverse Transcription Polymerase Chain Reaction (RT-PCR). Mottle/yellowing symptom was found more on the plants assessed (46%) followed by leaf curling (21%), leaf necrosis (09%), leaf deformation (11%) and irregular patches (13%). RYMVD was found highly distributed in the State with average incidence of 54.38%. The highest incidence was recorded in in Yauri (67.50%) followed by Argungu (55.00%), Bagudo (52.50%) and the lowest was recorded in Suru (42.50%). The average symptom severity across all the four Local Governments visited was 2.8, the highest was recorded in Yauri (3.2), followed by Argungu (2.9), Bagudo (2.7) and Suru 2.3. The information obtained in this study would assist rice breeding programs to develop durable RYMV rice resistant cultivars and guide in the identification of RYMVD hot spot locations for seed multiplication trials in Kebbi State.

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Comparing patterns and scales of plant virus phylogeography: Rice yellow mottle virus in Madagascar and in continental Africa

Virus Evolution ◽

10.1093/ve/vez023 ◽

2019 ◽

Vol 5 (2) ◽

Cited By ~ 4

Author(s):

Mbolarinosy Rakotomalala ◽

Bram Vrancken ◽

Agnès Pinel-Galzi ◽

Perle Ramavovololona ◽

Eugénie Hébrard ◽

...

Keyword(s):

Plant Virus ◽

Virus Disease ◽

Continuous Process ◽

Plant Viruses ◽

Mottle Virus ◽

Rice Yellow Mottle Virus ◽

Calendar Time ◽

Long Distance ◽

Transmission Potential ◽

Yellow Mottle

Abstract Rice yellow mottle virus (RYMV) in Madagascar Island provides an opportunity to study the spread of a plant virus disease after a relatively recent introduction in a large and isolated country with a heterogeneous host landscape ecology. Here, we take advantage of field survey data on the occurrence of RYMV disease throughout Madagascar dating back to the 1970s, and of virus genetic data from ninety-four isolates collected since 1989 in most regions of the country to reconstruct the epidemic history. We find that the Malagasy isolates belong to a unique recombinant strain that most likely entered Madagascar through a long-distance introduction from the most eastern part of mainland Africa. We infer the spread of RYMV as a continuous process using a Bayesian statistical framework. In order to calibrate the time scale in calendar time units in this analysis, we pool the information about the RYMV evolutionary rate from several geographical partitions. Whereas the field surveys and the phylogeographic reconstructions both point to a rapid southward invasion across hundreds of kilometers throughout Madagascar within three to four decades, they differ on the inferred origin location and time of the epidemic. The phylogeographic reconstructions suggest a lineage displacement and unveil a re-invasion of the northern regions that may have remained unnoticed otherwise. Despite ecological differences that could affect the transmission potential of RYMV in Madagascar and in mainland Africa, we estimate similar invasion and dispersal rates. We could not identify environmental factors that have a relevant impact on the lineage dispersal velocity of RYMV in Madagascar. This study highlights the value and complementarity of (historical) nongenetic and (more contemporaneous) genetic surveillance data for reconstructing the history of spread of plant viruses.

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