What is Interdiploid hybridization?

Since 1971, extensive inter-diploid crosses were made to synthesize new diploid forms at the Tamil Nadu Agricultural University, Coimbatore using the following parents:

Initially, breeding was started with the objective to incorporate the resistance against wilt in Gros Michel (as female parent) by using wild M.acuminata diploid as male parent. The tetraploid (progeny of hybrid) was very tall but it was resistant to wilt. The dwarfness was incorporated by using a dwarf mutant Highgate as a substitute for Gros Michel (Ray, 1999). Later work utilized Lowgate which was smaller than highgate and gave progeny the same height as Grand Naine. Since Lowgate gave fewer seeds than Highgate and its bunch qualities were also inferior to Highgate.

The pollination is carried out between 7.00 to 10.00 AM, undehisced anthers of male flowers are collected and twisted gently to force them to dehisce. Using a soft stable hair brush, the pollen grains are taken out and smeared gently over the stigmatic surface of the female flowers opened on the day of pollination. The pollinated flowers are to be covered with soft cloth bag (Sathiamoorthi and Balamohan, 1993). Most of the seed (74.9%) are found in 1/3 part of the distal end of fruits, about 20.9% in 1/3 mid portion and rest at (4.2%) in the proximal 1/3.

Matti (AA) is a diploid cultivar commercially grown in the southern most part of India. It exhibits a strong resistance to Sigatoka disease but is highly susceptible to nematodes. It sets seeds when pollinated, though it is highly male sterile. This cultivar is extensively used as female parent in the diploid breeding programmes. M.acuminata subsp. burmannica and M. acuminata spp.malaccensis has been shown to have resistance to panama wilt Races 1 and 2, sigatoka diseases and nematodes.

Other diploid clones involved in the diploid male parents synthesis at Coimbatore are the indigenous cultivars Anaikomban (AA) and Namarai (AA). Anaikomban is resistant to nematodes and fusarium wilt but susceptible to yellow sigatoka. Namarai is a small slender plant, grown in Pulney and Sirumalai hills of Tamil Nadu. It is susceptible to both Sigatoka disease and nematodes but no incidence of Panama disease is known so far.

The introduced diploids are Pisang lilin (AA) and Tongat (AA), known for their resistance to Panama disease and nematodes. Many synthetic hybrids (diploids) have been developed which have good horticultural characters including resistance to Sigatoka, Panama wilt and burrowing nematodes. These hybrids are now used as the male parents to cross with local triploid varieties or inter crossed to synthesise new triploid hybrids.

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