Drought has emerged as one of the major constraints in banana production. Its effects are pronounced substantially in the tropics and sub-tropics of the world due to climate change. Bananas are quite sensitive to drought; however, genotypes with “B” genome are more tolerant to abiotic stresses than those solely based on “A” genome. In particular, bananas with “ABB” genomes are more tolerant to drought and other abiotic stresses than other genotypes. A good phenotyping plan is a prerequisite for any improvement program for targeted traits. In the present article, known drought tolerant traits of other crop plants are validated in bananas with different genomic backgrounds and presented. Since, banana is recalcitrant to breeding, strategies for making hybrids between different genomic backgrounds are also discussed. Stomatal conductance, cell membrane stability (CMS), leaf emergence rate, rate of leaf senescence, RWC, and bunch yield under soil moisture deficit stress are some of the traits associated with drought tolerance. Among these stress bunch yield under drought should be given top priority for phenotyping. In the light of recently released Musa genome draft sequence, the molecular breeders may have interest in developing molecular markers for drought resistance.

An efficient regeneration protocol for zygotic embryos at varying maturity stages was developed for wild banana (Pisang Jajee (AA)). Embryo ontogeny was studied to determine the best maturity stage for embryo rescue, suitable media and culture conditions (light and dark) for germination and regeneration. The conversion of endosperm from transparent fluid into a semi-solid state was followed by visible embryo development, which commenced only after 70% embryo maturity. Zygotic embryos of Pisang Jajee at different maturity levels were excised and cultured on medium fortified with different concentrations of 6-benzyl adenine (BA) and indole acetic acid (IAA). Zygotic embryos produced callus or plantlets 25 days after initiation. The frequency of callus induction was greater in immature embryos irrespective of the media composition and decreased with increasing maturity. Fully matured embryos regenerated directly into plantlets without producing callus. Immature embryos required medium supplemented with plant growth regulators (PGRs) for successful regeneration. Although the culture conditions had no influence, dark conditions favoured callus induction and plant regeneration.

To find out the genetic diversity of Indian Foc isolates of banana, a total of 107 isolates of Fusarium which includes 98 Foc isolates obtained from different banana growing regions of India and seven Foc isolates belong to all known VCGs obtained from Australia and two non-pathogenic Fusarium oxysporum (npFo) isolates were subjected to ISSR analysis. In the initial screening of ISSR primers, out of 34, 10 primers which generated more polymorphic bands were selected for further analysis. The Phylogenetic analysis carried out based on the fingerprints obtained through ISSR analysis indicated the presence of wide genetic diversity among the Foc isolates of India and also its polyphyletic nature. Totally, seven different clusters were obtained and these clusters differentiated the Foc isolates of India based on the races/VCGs. Besides, the cluster analysis clearly distinguished the freshly emerged Foc strain obtained from cv. Grand Naine (Cavendish-AAA) and Poovan (Mysore-AAB) from the other Foc isolates. The non-pathogenic F. oxysporum isolates which have been included for comparison purpose also clustered separately. All these above said findings indicates for the first time the discriminatory power of ISSR to clearly distinguish and separate the Foc isolates according to its race/VCGs and also its virulence. This study would be useful not only to design and develop effective management strategies but also useful for quarantine purposes.

Banana wilt disease caused by Fusarium oxysporum f. sp. cubense is one of the most significant threats to banana production worldwide. Strains of F. oxysporum f. sp. cubense have been grouped into race-1, -2, or -4 on the basis of differential virulence among different genotypes of banana. In India, though the disease is reported among susceptible varieties of races 1 and 2, the disease is not reported from Cavendish cultivars, which are the differential host to race-4. Recent surveys of the Cumbum areas (Theni District, Tamil Nadu) revealed symptoms (e.g., yellowing and drooping of leaves around the pseudostem and longitudinal splitting of pseudostem) on cv. Grand Naine (Cavendish group – AAA). F. oxysporum f. sp. cubense was recovered and single-spore isolates had characteristic white-to-purple aerial mycelia producing single-celled, oval microconidia in false heads on branched monophialides and sickle-shaped macroconidia with an attenuated apical cell and a foot-shaped basal cell. Pathogenicity was demonstrated on cv. Grand Naine by inoculation with sand maize meal inoculum (20 g per pot containing 106 spores per g). Vegetative compatibility, using 33 nit-M testers of all known vegetative compatibility groups (2), showed that nit-1 mutants generated from a wild strain of F. oxysporum f. sp. cubense isolated from cv. Grand Naine formed robust heterokaryons with nit-M tester 0124 of the Department of Employment, Economic Development and Innovation, Brisbane, Australia and also with nit-M tester obtained from an isolate of F. oxysporum f. sp. cubense from Karpuravalli (Pisang Awak-ABB). Further characterization of this new Cavendish strain was studied on the basis of volatile odor production (3) using VCGs 0125 for race-1 (‘inodoratum group’) and 0120 for race 4 (‘odoratum group’) as positive controls and sterile medium as a negative control. This new F. oxysporum f. sp. cubense strain of Cavendish belonged to ‘inodoratum’ group of F. oxysporum f. sp. cubense. Pathogenicity was demonstrated on potted plants (10 per cultivar) of cvs. Rasthali (Silk-AAB), Karpuravalli (Pisang Awak-ABB), Ney Poovan (AB), Poovan (Mysore-AAB), Red Banana (AAA), Nendran (French plantain-AAB), Monthan (ABB), and Grand Naine (Cavendish-AAA) by inoculation with sand maize meal inoculum (20 g per pot containing 106 spores per g) in three replicate experiments. Plants were uprooted 2 months postinoculation and disease severity was estimated by rating internal vascular discoloration in the corm (1). The result showed that all cultivars, except Red Banana and Nendran, had the highest rating for disease severity, 6. To our knowledge, this is the first report of a virulent strain of F. oxysporum f. sp. cubense VCG 0124 of race-1on Cavendish banana. References: (1) J. Carlier et al. Technical Guidelines Number 6. INIBAP, Montpellier, France, 2002. (2) J. C. Correll et al. Phytopathology 77:1640, 1987. (3) N. Y. Moore. Aust. J. Bot 39:161, 1991.

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