Abstract
Bananas and plantains are considered an important crop around the world. Banana production is affected by several constraints, of which Black Sigatoka Disease, caused by the fungus Mycosphaerella fijiensis, is considered one of the most important diseases in banana plantations. The banana accession ‘Calcutta-4’ has a natural resistance to Black Sigatoka; however, the fruit is not valuable for commercialization. Gene identification and expression studies in ‘Calcutta-4’ might reveal possible gene candidates for resistant to the disease and elucidate mechanisms for resistance. A subtracted cDNA library was generated from leaves after 6, 9 and 12 days inoculated with M. fijiensis conidia on greenhouse banana plants of the accession ‘Calcutta-4’. Bioinformatic analysis revealed 99 good quality sequences. Blast2go analysis revealed that 31% of the sequences could not be categorized and, according to the Biological Process Category, 32 and 28 ESTs are related to general metabolic and cellular processes, respectively; while 10 ESTs response to stimulus. Seven sequences were redundant and one was similar to genes that may be involved in pathogen resistance including the putative disease resistance protein RGA1. Genes encoding zinc finger domains were identified and may play an important role in pathogen resistance by inducing the expression of downstream genes. Expression analysis of four selected genes was performed using RT-qPCR during the early stage of the disease development at 6, 9, 12 and 15 days post inoculation showing a peak of up regulation at 9 or 12 days post inoculation. Three of the four genes showed an up-regulation of expression in ‘Calcutta-4’ when compared to ‘Williams’ after inoculation with M. fijiensis, suggesting a fine regulation of specific gene candidates that may lead to a resistance response. The genes identified in early responses in a plant-pathogen interaction may be relevant for the resistance response of ‘Calcutta-4’ to Black Sigatoka. Genes with different functions may play a role in plant response to the disease. The present study suggests a fine up regulation of these genes that might be needed to perform an incompatible interaction. Further gene functional studies need to be performed to validate their use as candidate resistance genes in susceptible banana cultivars.
Highlights
From 2009 until 2011 more than 18000 tons of bananas were marketed
Further gene functional studies need to be performed to validate their use as candidate resistance genes in susceptible banana cultivars
Blast2go analysis revealed that 31% of the sequences could not be categorized and, according to the Biological Process Category, 32 and 28 expressed sequence tags (ESTs) are related to general metabolic and cellular processes, respectively; while 10 ESTs response to stimulus (Fig 4 and Fig 5A)
Summary
From 2009 until 2011 more than 18000 tons of bananas were marketed. Most of the exporter banana production is generated in development countries such Ecuador, Colombia, Costa Rica and Guatemala, where all the production chain provides incomes to the local economy [1]. The European Union and the United States of America represent the biggest and most significant importers in the world, still the demand of the fruit will increase in China and other emerging countries until 2019 [2] This crop represents an important market worldwide with a promising raise of production and trade. In Ecuador, important banana and plantain cultivars are threatened by BSD, especially in smallholders who could not control the disease chemically or in an integrated management. These cultivars include ‘Williams’ (genotype AAA), ‘Gran Enano’ (AAA), ‘Barraganete’ (AAB), and ‘Dominico’ (AAB)
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