Selection of Diploid and Tetraploid Banana Hybrids Resistant to Pseudocercospora fijiensis

Black Sigatoka, a disease caused by the fungus Pseudocercospora fijiensis, can lead to the complete loss of banana and plantain production in the absence of chemical control. The development of resistant cultivars is the focus of many banana breeding programs and is an alternative to the use of fungicides. In order to define a refined method of selection in genetic breeding programs, this study evaluated 23 improved diploids, seven tetraploids, and two commercial cultivars in the presence of P. fijiensis. Four selection criteria were considered: means of the disease severity index (ID) and area under the disease progress curve (AUDPC) estimated over the total period of the experiment, only in summer, only in winter, and the emission and harvesting of bunches. The selection of genotypes was more effective in the winter, and the evaluation of four leaves no. 3 emitted after six months of growth was efficient at differentiating the resistant and susceptible genotypes. For the improved diploids and tetraploid hybrids, DI varied from 0.0 to 48.8 and from 15.1 to 63.5, respectively, and the AACPD for the improved hybrids and tetraploid hybrids varied from 0.0 to 2439.5 and 1000.2 to 3717.7, respectively. The tetraploid hybrid of the Prata-type CNPMF0906 and the commercial cultivar, which is a hybrid of the BRS Princesa Silk type, showed quantitative resistance and can be used by banana producers. Results suggest that the guidelines adopted for the selection of genotypes resistant to black Sigatoka may include methodologies that reduce the evaluation time. In addition, new sources of resistance to the disease and the influence of its genetic inheritance in future crosses were found.

A polyketide synthase gene cluster required for pathogenicity of Pseudocercospora fijiensis on banana

Pseudocercospora fijiensis is the causal agent of the highly destructive black Sigatoka disease of banana. Previous research has focused on polyketide synthase gene clusters in the fungus, given the importance of polyketide pathways in related plant pathogenic fungi. A time course study of expression of the previously identified PKS7-1, PKS8-2, and PKS10-2 gene clusters showed high expression of all three PKS genes and the associated clustered genes in infected banana plants from 2 weeks post-inoculation through 9 weeks. Engineered transformants silenced for PKS8-2 and PKS10-2 were developed and tested for pathogenicity. Inoculation of banana plants with silencing transformants for PKS10-2 showed significant reduction in disease symptoms and severity that correlated with the degree of silencing in the conidia used for inoculation, supporting a critical role for PKS10-2 in disease development. Unlike PKS10-2, a clear role for PKS8-2 could not be determined. Two of four PKS8-2 silencing transformants showed reduced disease development, but disease did not correlate with the degree of PKS8-2 silencing in the transformants. Overall, the degree of silencing obtained for the PKS8-2 transformants was less than that obtained for the PKS10-2 transformants, which may have limited the utility of the silencing strategy to identify a role for PKS8-2 in disease. Orthologous PKS10-2 clusters had previously been identified in the related banana pathogens Pseudocercospora musae and Pseudocercospora eumusae. Genome analysis identified orthologous gene clusters to that of PKS10-2 in the newly sequenced genomes of Pseudocercospora fuligena and Pseudocercospora cruenta, pathogens of tomato and cowpea, respectively. Our results support an important role for the PKS10-2 polyketide pathway in pathogenicity of Pseudocercospora fijiensis, and suggest a possible role for this pathway in disease development by other Pseudocercospora species.

Yield and Fruit Quality Traits of Two Banana Cultivars Grown at Two Locations in Puerto Rico under Black Leaf Streak Disease Pressure

Banana (Musa acuminata AAA) is the most exported fruit worldwide and represents a major source of revenue for Central American and South American countries as well as the Caribbean region, among others. Black leaf streak disease (BLSD) or black sigatoka, caused by Pseudocercospora fijiensis (formerly Mycosphaerella fijiensis), is responsible for significant losses to this crop due to the high susceptibility of the most economically important cultivars. BLSD does not immediately kill banana plants, but it causes severe leaf necrosis that results in reduced photosynthetic area, thereby adversely impacting bunch weight and fruit production. Without cultural and chemical control, yields can be reduced by 20% to 80%, depending on severity. This study evaluated ‘FHIA-17’, a BLSD-resistant synthetic hybrid (AAAA), against ‘Grand Nain’, a standard commercial cultivar with no BLSD tolerance, at two locations in Puerto Rico on Ultisol (Corozal site) and Oxisol (Isabela site) soils where BLSD was not managed. Significantly lower bunch yield (45,990 kg·ha−1) and significantly fewer fruit (220,671 fruit/ha) were obtained at Corozal than at Isabela (53,755 kg·ha−1; 380,241 fruit/ha). Lower production at Corozal was the result of higher severity of BLSD at this location than at Isabela and to soil factors interfering with optimum nutrient uptake. Average fruit production of ‘FHIA-17’ was significantly higher than that of ‘Grand Nain’ at both locations, with bunch yields of 68,105 and 72, 634 kg·ha−1 at Corozal and Isabela, respectively. Fruit of the third-upper hand was significantly longer for ‘FHIA-17’ at Corozal but not different at Isabela; however, ‘FHIA-17’ fruit in this hand were of significantly greater diameter. Fruit in the last hand of ‘FHIA-17’ were significantly longer than in ‘Grand Nain’ at Corozal, but of significantly greater diameter at both locations. At both locations, the mean fruit weight was significantly higher in ‘FHIA-17’ than in ‘Grand Nain’. The number of functional leaves present at flowering and at harvest was significantly higher in ‘FHIA-17’ than in ‘Grand Nain’ at both locations, indicating more availability of photosynthetic area in ‘FHIA-17’ during the fruit-filling period. The harvest cycle of ‘FHIA-17’ was significantly longer than for ‘Grand Nain’. It took 315 and 204 more days in Corozal and Isabela, respectively, to harvest three cycles (mother crop and two ratoon crops) of ‘FHIA-17’ than for ‘Grand Nain’. No significant differences were found for starch and soluble sugars in green unripe or fully mature fruit among cultivars. In this long-term study, ‘FHIA-17’ showed to have good production and resistance against BLSD and is a viable alternative to current commercial cultivars. Its relative advantage of reduced production costs by not needing fungicide applications should be weighed against its longer harvest cycle to produce a fruit bunch.

The Effects, Distribution and Management Options for Major Banana Diseases in Tanzania

Emergences of Fusarium wilt, Bacterial wilt and Black Sigatoka diseases have caused banana yield loss of up 100% in Tanzania. Though there have been accumulated empirical data on yield decline due to diseases, lack of disease knowledge and selection of appropriate control methods has been a limiting factor in improving banana production. Therefore, this review focused on identifying different management options for major banana diseases, for purpose of providing reference and decision making tools to farmers, extension officers, researchers and decision makers. Using online resources, we identified several methods which are affordable, applicable and reliable for disease management in the country. These includes sanitation, intercropping, crop rotation, prevention, irrigation, drainage improvement, quarantine, use of silicon/calcium and awareness campaigns. Other method was biological control, which need further research on its applicability and impact on the environment. Moreover the use of resistant cultivars though being important, there is little achievement which have been made on breeding for resistance, because banana are polyploidy, parthenocarpic, have long generation time, loss of resistance and poor acceptability of new cultivars. We also found that, no single method is perfect for management of diseases; this is due to the fact that, in agricultural system, disease challenges rarely occur singly. So the approach to disease management should be pragmatic and geared towards integration of several appropriate methods. We hereby conclude that, researches should focus on identifying the best and feasible combination of control methods that can be used by Smallholder farmers.

The Status of Banana Production in Tanzania; a Review of Threats and Opportunities

The word “banana” refers to a crop that cuddles a number of species commonly known as Musa spp. In Tanzania, the crop is the fourth most important crop for food and income generation for more than 30 percent of the total population. In East Africa, Tanzania is the second banana producer after Uganda. The country has the highest world’s consumption rate between 280-500 kg per person. Despite the crop’s importance its production has declined from 18 t/ha in the 1960s to 5-7 t/ha/year in 2016. This review examined the status of banana production by identifying threats and opportunities with the aim of providing readily available resource for Researchers and Agriculture Extension Officers for better banana production. Through online resources, the review identified the challenges impeding banana production and ascertaining prevailing opportunities. Banana production in Tanzania is faced with many challenges including major pests (weevil and nematode) and diseases (fusarium wilt disease, black sigatoka, and banana xanthomonas wilt disease), poor soil fertility, moisture stress, poor management practices, lack of improved banana varieties and many social economic factors. The review identified that, since 1990s there are few introduced improved banana varieties and that most of these varieties are faced with low consumer’s acceptability. Again the country is faced with shortage of banana breeding centers that could produce desirable banana hybrid cultivars. This review also identified the lack of banana information resources and research platforms that involves all banana stakeholders, making targeting of varietal attributes to consumer preferences very difficult. Therefore, in order to improve production there must be an inter-link among different research disciplines, involving governmental and non-governmental organizations, coming together and seek solutions to current and future problems for sustainable production of banana.

Fungitoxic Potentialities of NECO 50 EC in an Integrated Black Sigatoka Management Strategy in Industrial Dessert Banana Plantation

Black leaf streak disease (BLSD) is the major constraint on banana production around the world. In Côte d'Ivoire, this disease is found in all banana-growing areas and its management involves the use of large volumes of agrochemicals. This mode of production is increasingly denounced by consumers from regarding fruit contamination by phytopharmaceuticals. The objective of this study is to promote the use of NECO 50 EC, a plant extract-based biofungicide in an integrated black Sigatoka management system. The fungitoxic effect of NECO 50 EC was assessed in vitro on Mycosphaerella fijiensis conidia germination and the evolution of black leaf streak disease symptoms under natural infestation. NECO 50 EC was applied over a surface area of 25 ha at a rate of 0.3 l/ha. Its weekly effect on the evolution of the rank of the youngest leaf affected (YLA), the rank of the youngest necrotic leaf (YLN), the number of functional leaves at flowering (NFLF) and the number of functional leaves at harvest (NFLH) was determined and then compared to those of a morpholine (Volley 88 OL) applied over a surface area of 25 ha at a dose of 0.5 l/ha. NECO 50 EC showed an anti-germinating effect on Mycosphaerella fijiensis conidia at low doses, useful in reducing disease spreading. Its application in banana tree plantations reduced disease pressure on the plots. It ensured the protection of new leaves generated (YLA > 4), favored ranks of YLN greater than 9. More than 14 leaves were counted at flowering and more than 7 leaves at harvest were observed. NECO 50 EC, a plant extract-based biological fungicide, may be an effective alternative for black leaf streak disease control in industrial banana tree plantations.

Black Sigatoka Classification Using Convolutional Neural Networks

In this paper we present a methodology for the automatic recognition of black Sigatoka in commercial banana crops. This method uses a LeNet convolutional neural network to detect the progress of infection by the disease in different regions of a leaf image; using this information, we trained a decision tree in order to classify the level of infection severity. The methodology was validated with an annotated database, which was built in the process of this work and which can be compared with other state-of-the-art alternatives. The results show that the method is robust against atypical values and photometric variations.