Breeding of Vegetable, Spice and Tuber crops (2+1)

Breeding methods

• Introduction, mass selection, selfing and massing, inbreeding followed by hybridization to exploit heterosis have been used for improvement of onion.

 

Plant introduction

• Early Grano is an introduction into India. In long-day types, Brown Spanish was also a successful introduction.

Mass selection

• Common in cross-pollinated crops. Most of the onion varieties in India have been developed by mass selection.

Selfing and massing

• Suggested by Jones and Mann (1963). This method is very good for improvement in a crop, where inbreeding depression is common. Improvement in cultivar can be effected by selfing followed by massing. The procedure is as follows.
• First year (bulb crop): Select 100 best bulbs of desired type.
• Second year (seed crop): Grow selected bulbs, self one or more umbels per plant to initiate a separate line each.
• Third year (bulb crop): Grow the progenies of each inbred line separately. Discard the poor performing lines during the growing season, at harvest or in storage. Select at least 25 best lines and keep 15-20 bulbs of each for selfing and open pollination for next year.
• Fourth year (seed crop): Self pollinate 1-2 umbels in each plant and allow others to open pollinate. Mass open pollinated seed and increase for large-scale production for more than two generations to avoid much inbreeding depression.
• Fifth year (bulb crop): Grow the selfed progenies separately. Select again the best 25 lines and 15-20 bulbs of each lines as above in the third year.
• Sixth year (seed crop): Composite and plant bulbs of all selections in a field or in a cage for free open pollination in between the unrelated lines. The open pollinated seed can be massed and increased as foundation seed.

Inbreeding

• In any onion improvement programme, a considerable amount of inbreeding or selfing is necessary. Brown paper bags and three ring muslin cloth bags are used for selfing.

Hybridization

• Used when we want to introduce characters from other varieties.
• Intervarietal : Very common
• Interspecific : Very rare
• Utilized in A. cepa x A. fistulosum.

Heterosis breeding

• The F1 hybrids are high yielding with uniformity in bulb size, the two most desired characters.
• One of the main components for exploitation of heterosis in onion is isolation of male-sterile lines.
• The male-sterile lines have been isolated in Pusa Red at IARI.
• Male-sterile lines have been also isolated at IIHR, Bangalore, but there is no hybrid in commercial production yet; work is in progress to isolate the best combiners.
• Heterosis breeding involves three important stages, namely:
• Production of inbred lines
• Testing combining ability of inbred lines
• Production of the seeds of F1 hybrids
• A line = male sterile line (S msms) caused by sterile cytoplasm (S) and nuclear recessive gene (msms).
• B line = maintainer line (N msms)
• C line = male parent (N MsMs or N Msms or N msms or S MsMs or S Msms)
• Maintenance AxB 1:1 F1 production AxC 4:1 or 8:2.