Identification of sources resistant to a virulent Fusarium wilt strain (VCG 0124) infecting Cavendish bananas

Bananas are vital for food security in many countries, and half of banana production relies solely on ‘Cavendish’ (AAA), which is presently threatened by the fungal pathogen Fusarium oxysporum f. sp. cubense (Foc) tropical race 4. This particular virulent Foc strain was also found to attack other banana varieties of commercial importance. As there is no single effective management practice available so far, this study was undertaken to determine resistant sources from the genotype collection available at the ICAR-National Research Centre for Banana, Tiruchirappalli, Tamil Nadu, India for direct use by farmers and/or in breeding programmes to develop resistant hybrids. A total of 258 genotypes of different ploidies and genomic constitutions were tested against Foc race 1 (VCG 0124). In total, 19 genotypes (AA Unique-6, BB type-2, AAA Unique-1, AAA Cavendish-1, AAB Mysore-3, AAB Pome-1, AAB Plantain-4 and AAAB-1) were found to be immune; eight genotypes (AA Unique-1, BB type-3, AAA Cavendish-1, AAB Mysore-1, AAB Unique-1, AAB Plantain-1) were highly resistant; and nine genotypes (AA Unique-1, AAA Cavendish-3, AAB Silk-1, AAB Pome-4) were resistant. The genotypes that are resistant to the virulent Foc race 1 (VCG 0124) strain can be exploited directly for commercialization and/or in breeding programs to develop resistant hybrids.

Strengthening of banana breeding through data digitalization

Improvement of edible bananas (a triploid and sterile crop) through conventional breeding is a challenging task owing to its recalcitrant nature for seed set, prolonged crop duration. In addition, the need of huge man power at different stages of progeny development and evaluation often leads to mislabeling, poor data management and loss of vital data. All this can be overcome by the application of advanced information technology source. This ensured secure and efficient data management such as storage, retrieval and data analysis and further could assist in tracking the breeding status in real time. Thus, a user-friendly web-based banana breeding tracker (BBT) has been developed using MySQL database with Hypertext Preprocessor (PHP). This BBT works on all operating systems with access to multiple users from anywhere at any time. Quick responsive (QR) code labels can be generated by the tracker, which can be decoded using QR scanner. Also for each and every updated progress in breeding stages, a new QR code can be generated, which in turn reduce labeling errors. Moreover, the tracker has additional tools to search, sort and filter the data from the data sets for efficient retrieval and analysis. This tracker is being upgraded with phenotypic and genotypic data that will be made available in the public domain for hastening the banana improvement program.

Improvement of banana cv. Rasthali (Silk, AAB) against Fusarium oxysporum f.sp. cubense (VCG 0124/5) through induced mutagenesis: Determination of LD50 specific to mutagen, explants, toxins and in vitro and in vivo screening for Fusarium wilt resistance

Shoot tips and in vitro grown proliferating buds of banana cv. Rasthali (Silk, AAB) were treated with various concentrations and durations of chemical mutagens viz., EMS, NaN3 and DES. LD50 for shoot tips based on 50% reduction in fresh weight was determined as 2% for 3 h, 0.02% for 5 h and 0.15% for 5 h, while for proliferating buds, they were 0.6% for 30 min, 0.01% for 2 h and 0.06% for 2 h for the mutagens EMS, NaN3 and DES, respectively. Subsequently, the mutated explants were screened in vitro against fusarium wilt using selection agents like fusaric acid and culture filtrate. LD50 for in vitro selection agents calculated based on 50% survival of explants was 0.050 mM and 7% for fusaric acid and culture filtrate, respectively and beyond which a rapid decline in growth was observed. This was followed by pot screening which led to the identification of three putative resistant mutants with an internal disease score of 1 (corm completely clean, no vascular discolouration). The putative mutants identified in the present study have also been mass multiplied in vitro.

Mining of EST-SSR markers of Musa and their transferability studies among the members of order the Zingiberales

Expressed sequence tags (ESTs) databases of 11 Musa complementary DNA libraries were retrieved from National Center of Biotechnology Information and used for mining simple sequence repeats (SSRs). Out of 21,056 unique ESTs, SSR regions were found only in 5,158 ESTs. Among these SSR containing ESTs, the occurrence of trinucleotide repeats are the most abundant followed by mono-, di-, tetra-, hexa-, and pentanucleotides. Moreover, this study showed that the rate of class II SSRs (<20 nucleotides) was higher than the class I SSRs (<20 nucleotides), and proportion of class I and II SSRs as abundant for tri-repeats. As a representative sample, primers were synthesized for 24 ESTs, carrying >12 nucleotides of SSR region, and tested among the various genomic group of Musa accessions. The result showed that 88 % of primers were functional primers, and 43 % are showing polymorphism among the Musa accessions. Transferability studies of Musa EST-SSRs among the genera of the order Zingiberales exhibited 100 and 58 % transferability in Musaceae and Zingiberaceae, respectively. The sequence comparison of SSR regions among the different Musa accessions confirmed that polymorphism is mainly due to the variation in repeat length. High percentage of cross-species, cross-genera, and cross-family transferability also suggested that these Musa EST-SSR markers will be a valuable resource for the comparative mapping by developing COS markers, in evolutionary studies and in improvement of the members of Zingiberaceae and Musaceae.