Genetically engineered bananas resistant to Xanthomonas wilt disease and nematodes

Banana is an important staple food crop feeding more than 100 million Africans, but is subject to severe productivity constraints due to a range of pests and diseases. Banana Xanthomonas wilt caused by Xanthomonas campestris pv. musacearum is capable of entirely destroying a plantation while nematodes can cause losses up to 50% and increase susceptibility to other pests and diseases. Development of improved varieties of banana is fundamental in order to tackle these challenges. However, the sterile nature of the crop and the lack of resistance in Musa germplasm make improvement by traditional breeding techniques either impossible or extremely slow. Recent developments using genetic engineering have begun to address these problems. Transgenic banana expressing sweet pepper Hrap and Pflp genes have demonstrated complete resistance against X. campestris pv. musacearum in the field. Transgenic plantains expressing a cysteine proteinase inhibitors and/or synthetic peptide showed enhanced resistance to a mixed species population of nematodes in the field. Here, we review the genetic engineering technologies which have potential to improve agriculture and food security in Africa

Progress in understanding Pseudocercospora banana pathogens and the development of resistant Musa germplasm

Article purchased; Published online: 9 Feb 2018Banana and plantain (Musa spp.) are important food crops in tropical and subtropical regions of the world where they generate millions of dollars annually to both subsistence farmers and exporters. Since 1902, Pseudocercospora banana pathogens, Pseudocercospora fijiensis, P. musae and P. eumusae, have emerged as major production constraints to banana and plantain. Despite concerted efforts to counter these pathogens, they have continued to negatively impact banana yield. In this review, the economic importance, distribution and the interactions between Pseudocercospora banana pathogens and Musa species are discussed. Interactions are further scrutinized in the light of an emerging climate change scenario and efforts towards the development of resistant banana germplasm are discussed. Finally, some of the opportunities and gaps in knowledge that could be exploited to further understanding of this ubiquitous pathosystem are highlighted

Response of East African highland bananas to black Sigatoka and Cladosporium leaf speckle under tropical humid forest lowland conditions in West Africa

The responses of 19 East African highland (EAH) banana cultivars (AAA and AA genomes) and two reference cultivars to black sigatoka (Mycosphaerella fijiensis Morelet) and Cladosporium leaf speckle (Cladosporium musae Mason) were studied in 1993 at Onne (southeastern Nigeria) under ecological conditions of the tropical humid forest lowlands. Plants were evaluated before flowering during the rainy season when conditions were favorable for both plant growth and disease development. Disease development time was found to be the most useful variable to evaluate and distinguish the response of different Musa cultivars to black sigatoka. Black sigatoka symptoms developed on all cultivars observed into the final stage of leaf spots with dry centers, hence none was classified as resistant. On the susceptible reference cultivars 'Valery' (AAA dessert banana) and 'Agbagba' (AAB False Horn plantain) the final symptom stage of black sigatoka developed within 32 days. Sixteen of the EAH banana cultivars expressed a lower level of partial resistance with disease development times ranging from 52 to 65 days. Four EAH banana cultivars expressed a higher level of partial resistance with a disease development time longer than 65 days. A preliminary grouping was also carried out for the host response to C. musae. Two groups with different levels of host response were identified

First report of banana streak badnavirus in plantain landraces in southern Cameroon, Central Africa

Banana streak badnavirus (BSV) has been reported from Musa spp. in many parts of West Africa, including Benin, Côte d'Ivoire, Ghana, and Nigeria (1). Symptoms of BSV infection in Musa spp. are sometimes similar to and confused with those caused by cucumber mosaic virus (CMV). BSV is prevalent in areas of southern Nigeria bordering Cameroon, and the disease may also be present in other Central African countries. In June 1996, six leaf samples with viruslike yellow/chlorotic streak symptoms were collected from plantain in the four villages, Awae, M'Balmayo, Nkolfep, and Nkolfoulou, within a 60-km radius of Yaoundé, Cameroon's capital. The samples were indexed for BSV and CMV by both triple antibody sandwich indirect enzyme-linked immunosorbent assay (TAS-ELISA) and immunosorbent electron microscopy (ISEM) to ascertain the presence of these two viruses. The TAS-ELISA was performed with rabbit polyclonal antiserum (obtained from B. E. L. Lockhart, University of Minnesota) for trapping and mouse polyclonal antiserum (obtained from G. Thottappilly, IITA) for detection. Out of the six samples, one tested strongly positive (>×2 A405 of the healthy control) and four were weakly positive (×1.5 A405 of the healthy control) for BSV by TAS-ELISA. However, all six samples contained BSV particles when examined by ISEM with rabbit polyclonal antiserum (from B. E. L. Lockhart) for trapping. None of the samples tested positive for CMV. These results confirm that BSV is present in Cameroon and that BSV is likely to be the causal agent of the symptoms

A pest on Calliandra calothyrsus in Cameroon

Abstract. A beetle pest, Tragocephala guerini White (Col.: Cerambycidae) was observed damaging the branches of Calliandra calothyrsus Meissner in Cameroon, Central Africa. The pests biology and details of the damage on the host plant are described

Studies on a Nigerian isolate of banana streak badnavirus: II. Effect of intraplant variation on virus accumulation and reliability of diagnosis by ELISA

Monitoring of banana streak badnavirus (BSV) antigens and symptoms in naturally BSV‐infected plantain and banana (Musa spp.) plants showed a great variation in symptom expression, distribution and relative concentration of BSV between and within plants. Expression and distribution of symptoms was erratic within individual leaves as well as between different leaves of the same plant. The concentration of BSV antigens detected by triple antibody sandwich enzyme linked immunosorbent assay (TAS‐ELISA) varied in different plant parts including leaf lamina, midrib and pseudostem, roots and young ‘cigar' leaf. The concentration of BSV antigens was high in symptomatic tissues but was low or below the limits of detection in most asymptomatic tissues. During ‘hot dry' seasons when symptoms were not fully expressed, the concentration of BSV antigens in leaf tissues declined drastically, often below the detection limit of TAS‐ELISA. These results suggested that for more reliable detection of BSV antigens by TAS‐ELISA, it is advisable to index plants using composite tissue samples comprising as many leaves as possible for each plant and collected during cool and/or rainy seasons when symptom expression is generally severe

Symptomatology and development of banana streak badnavirus, under natural conditions in Ibadan, Nigeria

A field experiment with suckers taken from five improved plantain hybrids and one landrace with typical symptoms of banana streak badnavirus (BSV) infection was established at Ibadan (Nigeria) to investigate climatic factors affecting BSV symptom development and to identify parameters useful in genotype evaluation for BSV incidence. Weekly monitoring of individual plants for symptom incidence and severity indicated that symptom expression was more severe during the rainy season (July to October-November) than in the dry season (January to May-June). Symptoms included discrete yellow streaks on the leaves, internode shortening with rosette-like leaves, a necrotic cigar leaf and distorted (inverted) bunch. An evaluation of these symptoms and their grouping indicated that chlorotic streaks or oval to spindle-shaped lesions were predominant in most genotypes. Appearance of symptoms varied both within and between accessions. On TMPx 7002-1 and TMPx 548-9 the BSV symptoms were first observed about 80 days after transplanting (DAT), whereas for Agbagba, TMPx 548-4, TMPx 4698-1 and TMPx 2796-5, the symptoms were first observed more than 100 DAT. The final percentage of BSV-symptomatic plants was generally high (> 50%) on both the hybrids and the landrace Agbagba but TMPx 548-9 and TMPx 7002-1 had more than 80% symptomatic plants. Irrespective of genotype, symptomatic mother plants produced a higher percentage of mats where all suckers showed BSV symptoms than did asymptomatic mother plants. During the hot season, approximately 70% of the symptomatic plants and 15% of the asymptomatic plants indexed positive for BSV by enzyme-linked immunosorbent assay. Disease progress curves for temporal development of banana streak symptoms were sigmoid. The increase in incidence of symptomatic plants was best described by the Gompertz model. Statistical analysis of the parameters associated with the disease progress curves suggested that besides symptom incidence other parameters such as area under the disease progress curve and rate of symptom development were essential for evaluation of Musa accessions for BSV incidence