Genotype X environment response of 'Matooke' hybrids (Naritas) to Pseudocercospora fijiensis, the cause of black Sigatoka in banana

Open Access Journal; Published online: 03 Jun 2021Growing bananas resistant to Pseudocercospora fijiensis, the cause of black Sigatoka, is the preferred disease control strategy for resource-poor farmers. Banana breeding programs in east Africa have developed 27 Matooke hybrids (commonly known as NARITAs) with higher yields than local landraces. To assess the response of NARITA hybrids to P. fijiensis, 22 hybrids were evaluated under natural field conditions in four locations—Kawanda and Mbarara in Uganda, and Maruku, and Mitarula in Tanzania—between 2016 and 2018 for three crop cycles. Black Sigatoka was visually assessed and the area under the disease progress curve calculated for each plant over time. Significant differences (p < 0.001) were observed between genotypes, environments, and their interaction. The highest contributor to black Sigatoka severity (39.1%) was the environment, followed by the genotype (37.5%) and the genotype Χ environment interaction (GEI) (23.4%). NARITA 2, 7, 14, 21 and 23 were resistant and the most stable hybrids across locations. If other attributes such as the yield and taste are acceptable to end-users, these hybrids can be released to farmers in the region to replace highly susceptible landraces. Mitarula was identified as an ideal site for evaluating banana against black Sigatoka and should be used as a representative location to minimize costs of disease evaluations

Distribution of Pseudocercospora species causing Sigatoka leaf diseases of banana in Uganda and Tanzania

Open Access Article; Published online: 11 Oct 2019Sigatoka leaf diseases are a major constraint to banana production. A survey was conducted in Tanzania and Uganda to assess the distribution of Pseudocercospora species and severity of Sigatoka leaf diseases. Pseudocercospora species were identified using species‐specific primers. Sigatoka‐like leaf diseases were observed in all farms and on all cultivars, but disease severity varied significantly (P < 0.001) between countries, districts/regions within countries, altitudinal ranges and banana cultivars. In all regions except Kilimanjaro, P. fijiensis, the causal agent of black Sigatoka, was the only pathogen associated with Sigatoka disease. Mycosphaerella musae was associated with Sigatoka‐like symptoms in Kilimanjaro region. Black Sigatoka disease was more severe in Uganda, with a mean disease severity index (DSI) of 37.5%, than in Tanzania (DSI = 19.9%). In Uganda, black Sigatoka disease was equally severe in Luwero district (mean DSI = 40.4%) and Mbarara district (mean DSI = 37.9%). In Tanzania, black Sigatoka was most severe in Kagera region (mean DSI = 29.2%) and least in Mbeya region (mean DSI = 11.5%). Pseudocercospora fijiensis, the most devastating sigatoka pathogen, was detected at altitudes of up to 1877 m a.s.l. This range expansion of P. fijiensis, previously confined to altitudes lower than 1350 m a.s.l. in East Africa, is of concern, especially for smallholder banana farmers growing the susceptible East African Highland bananas (EAHB). Among the banana varieties sampled, the EAHB, FHIA hybrids and Mchare were the most susceptible. Here, the loss of resistance in Yangambi KM5, a banana variety previously resistant to P. fijiensis, is reported for the first time

First report of banana bunchy top disease caused by Banana bunchy top virus in Uganda

Banana bunchy top virus (BBTV) that causes banana bunchy top disease (BBTD) is ranked among the top 100 invasive species in the world. Despite being omnipresent in the Democratic Republic of Congo (DR Congo) and South-Western Rwanda for over 2 decades, BBTV had not been reported in neighbouring Uganda. However, in 2020, banana plants with BBTD characteristic symptoms were observed in Arua City located in the North Western part of Uganda, bordering DR Congo. BBTV in these plants was confirmed using PCR and the comparison of the genomic DNA nucleotide sequence with nucleotide sequences in NCBI data base (https://www.ncbi.nlm.nih.gov/). The gDNA nucleotide sequence had 98-99% similarity with BBTV isolates form different countries in Africa, Asia, South Pacific and the USA. These results constitute the first confirmation of BBTD in Uganda. This infection is anticipated to have been introduced from DR Congo, mainly through infected planting materials. Once established, BBTD is very difficult to control on small-scale farms. It is therefore crucial to urgently understand the current spread of the virus, determine its risk to banana production in Uganda and devise proactive measures for its management

Suppression of the ubiquitin E2 gene through RNA interference causes mortality in the banana weevil, Cosmopolites sordidus (Germar)

RNA interference (RNAi) is a natural defense mechanism triggered by double-stranded RNA (dsRNA) for protection of cells against foreign parasitic nucleic acids. The RNase III enzyme Dicer processes dsRNAs into short small interfering RNAs (siRNAs) that degrade the specific mRNA. RNAi has been demonstrated in a range of organisms including coleopterans and has a potential use in crop protection against insect pests and pathogens. In this study, we explored the use of RNAi for the control of the banana weevil that is not only the most important banana pest in East Africa, but has also eluded control through cultural, chemical and biological approaches. The ubiquitin E2 gene, essential for protein catabolism was identified, amplified and transcribed into dsRNA and fed to banana weevil larva in in vitro bioassays. The dsRNA significantly retarded banana weevil larval growth and caused up to 100% mortality at 21 days. Growth inhibition and mortality increased with dsRNA concentration (10 to 100 ng µL-1), though no significant differences were observed between the 50 and 100 ng µL-1 concentrations. We for the first time demonstrate RNAi in the banana weevil. Transgenic banana plants expressing siRNA or hairpin RNA could therefore potentially be used for controlling the banana weevil

Distribution of Pseudocercospora species causing Sigatoka leaf diseases of banana in Uganda and Tanzania

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