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

Introduction

• Each of the world’s basic vegetable crops originated in a relatively confined geographic region.
• The regions overlap for a number of crops.
• Vavilov (1926) suggested that centres of origin of crop plants coincide with the areas of greater genetic diversity.
• Vavilov identified 8 centres some of which were subdivided.
• However, Zhukovsky (1965), a close associate of Vavilov, proposed 12 mega gene centres of crop plant diversity.
• The new areas added to Vavilov’s eight centres were Australia, whole Africa and Siberia followed by revision of boundaries to make 12 centres.
• The global genetic wealth comprising about 3000 cultivated taxa, which mainly include both primitive/native cultivars and their wild and weedy species is distributed to these twelve primary centres of diversity (Zeven and Zhukovsky, 1975).
• This includes centres of origin and distribution of diversity in 218 vegetable crop species in different regions of diversity.
• During the process of domestication of vegetable crops other than the centres of origin/diversity, the primitive species moved to other areas during ancient past and due to continuous mutations, crossing with the related species, evolution, and selection by man and nature would have resulted in development of the secondary centre of diversity.
• The criteria for assigning a particular geographic region to a specific vegetable are the availability of considerable variability, presence of wild forms and existence of source of resistance to many of the diseases.
• Historical records, fossil records and archaeological findings add to this information.
• Knowledge regarding gene centres of cultivated plants and their possible wild ancestors (progenitors) serve as guidelines to collect main sources of genetic resistance to parasitic and non-parasitic diseases, insect pests and nematodes.
• In these centres of origin, the vegetable crops have long been exposed to the selective pressure of local pathogens and insect pests, and have developed inherent basic resistance.
• Leppik (1970) reviewed the role of gene centres of plants as sources of disease and pest resistance. He opined that systematic exploration of primary and secondary gene centres of a particular vegetable may provide additional gene pools for resistance breeding.
• Exploration and exploitation of gene centres therefore must for resistance proceed with systematic cooperation of taxonomists, geneticists and plant pathologists.