Browsing by Author "Ramathani, I."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Detection and identification of etiological agents (Liberibacter spp.) associated with citrus greening disease in Uganda
    (African Journals Online (AJOL), 2015) Kalyebi, A.; Aisu, G.; Ramathani, I.; Ogwang, J.; McOwen, N.; Russell, P.
    Citrus Huanglongbing (HLB), commonly referred to as citrus greening, is one of the major disease challenges of citrus. In Uganda, there was limited information on Liberibacter spp., the causal organisms of HLB disease, and its psyllid vectors despite the presence of HLB symptoms on citrus. The objective of this study was to identify the Liberibacter spp. and psylla vector species responsible for HLB in Uganda. Other native plant species that could be hosts to pathogens and the psyllid vectors, but are not in the citrus genus, were also investigated. A survey was conducted in 15 citrus growing districts, and symptomatic citrus leaf samples collected, as well as citrus psyllid nymphs and adults for isothermal detection of pathogens in the laboratory. Two types of bacterial pathogens responsible for HLB were detected, namely Candidatus Liberibacter africanus (CLaf), known as the African type; and Candidatus Liberibacter asiaticus (CLas), known as the Asian type. CLaf was found in Mukono and Wakiso districts in Central Uganda and in Mbarara in Western Uganda; while CLas was found in Budaka and Tororo districts in Eastern Uganda. Citrus psyllids, which are the major known disease vectors were present in seven out of the fifteen districts. Psyllid vector identification by morphological means indicated Trioza erytreae, the African psyllid to be the insect vector. Psyllids were common on tangerines (66.7%), Sour Orange (13.3%) and Rough Lemon (13.3%); and least on Washington Navel (6.7%). Three non-citrus plants, Stephania abyssinica (Dill. & A. Rich) walp var. tomentella (Oliv.) Deils (Menispermaceae), Diospyros mespiliformis (Ebenaceae) and Ficus spp (Moraceae) were found to be alternative host plants for the psyllid.
  • Thumbnail Image
    Item
    Occurrence of Rice Yellow Mottle Virus resistance breaking isolates in Lowland Catchment Zones of Uganda
    (African Crop Science Journal, 2021) Ramathani, I.; Mukasa, S. B.; Alicai, T.; Nanyiti, S.; Lamo, J.
    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. Seventyseven (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.