Screening of banana hybrids (phase II hybrids) for resistance to Meloidogyne incognita

Banana and plantains (Musa spp.), the second largest fruit crop in the world, are important staple foods in tropical regions of Africa, America, Asia and the Pacific. It is the most widely consumed and exported fruit in the world. Plant parasitic nematodes are one of the major biotic stresses affecting banana production. Breeding works carried out at the Department of Fruit Crops, Tamil Nadu Agricultural University, India. The potential diploids and hybrids developed were crossed with commercial triploids to develop primary tetraploids and improved diploids. The susceptible check cultivar used was ‘Rasthali’ (AAB), while the resistant reference cultivar used ‘Pisang Lilin’ (AA). Banana suckers of uniform size and weight were collected, pared and planted in earthen part containing 5 kg sterilized pot mixture. Egg masses of M. incognita were picked from roots, allowed to hatch in a beaker of distilled water and the hatched juveniles (J2) were inoculated in the rhizosphere of the hybrids by soil injection method at 5,000 nematodes/pot. Same set of replicated banana hybrids were also maintained as uninoculated check. The reactions of nineteen new synthetic banana phase II hybrids to M. incognita was studied under field conditions as well as in controlled inoculation tests in pots. Hybrid H 531 (‘Poovan’ × ‘Pisang Lilin’) was found to be resistant and six hybrids, H-02-34, H-03-05, H-03-13, H-04-12, H-04-24 and NPH-02-01 were found to be tolerant to the root-knot nematode, M. incognita while the remaining were rated as susceptible and highly susceptible ones. Total phenols and PO, PPO, PAL and enzymatic activity of the hybrids in defense mechanism in response to nematode invasion indicated higher activities in resistant genotypes compared to susceptible ones. The total phenol in the roots was estimated using Folin Ciocalteau reagent and measuring absorption at 660 nm in a spectrophotometer. For enzyme extraction, one gram of root sample per replicate was homogenized with 2ml of 0.1 M sodium phosphate buffer (pH 7.0) at 4°C. The supernatant was used as crude enzyme extract for assaying PO and PPO. Enzyme extracted in borate buffer was used for estimation of PAL. The PO activity was assessed according to Hammer-Schmidt and the PPO activity was assessed using the modified method of Mayer. Hybrid H 531 had the maximum biochemical content and enzyme activity among the hybrids included in this study. The resistant and tolerant hybrids had enhanced contents of total phenol, PO, PPO and PAL.