Abstract
Early blight (EB) is one of the dreadful diseases of tomato caused by several species of Alternaria including Alternaria linariae (which includes A. solani and A. tomatophila), as well as A. alternata. In some instances, annual economic yield losses due to EB have been estimated at 79%. Alternaria are known only to reproduce asexually, but a highly-virulent isolate has the potential to overcome existing resistance genes. Currently, cultural practices and fungicide applications are employed for the management of EB due to the lack of strong resistant cultivars. Resistance sources have been identified in wild species of tomato; some breeding lines and cultivars with moderate resistance have been developed through conventional breeding methods. Polygenic inheritance of EB resistance, insufficient resistance in cultivated species and the association of EB resistance with undesirable horticultural traits have thwarted the effective breeding of EB resistance in tomato. Several quantitative trait loci (QTL) conferring EB resistance have been detected in the populations derived from different wild species including Solanum habrochaites, Solanum arcanum and S. pimpinellifolium, but none of them could be used in EB resistance breeding due to low individual QTL effects. Pyramiding of those QTLs would provide strong resistance. More research is needed to identify additional sources of useful resistance, to incorporate resistant QTLs into breeding lines through marker-assisted selection (MAS) and to develop resistant cultivars with desirable horticultural traits including high yielding potential and early maturity. This paper will review the current understanding of causal agents of EB of tomato, resistance genetics and breeding, problems associated with breeding and future prospects.
Highlights
Tomato (Solanum lycopersicum Linnaeus), native to the Andean region of South America, is one of the most common horticultural crops and cultivated throughout the world
This paper discusses the early blight (EB) disease and the pathogen, genetic studies and breeding of tomato, problems associated with breeding, quantitative trait loci (QTL) (Quantitative Trait Loci) mapping efforts for early blight resistance and prospects to improve breeding for Early blight (EB) resistance
This study revealed that altersolanol A, altertoxin I and macrosporin are produced both in A. solani and A. tomatophila, but not in A. dauci
Summary
Tomato (Solanum lycopersicum Linnaeus), native to the Andean region of South America, is one of the most common horticultural crops and cultivated throughout the world. It can be grown in a wide range of climates from tropical to temperate; it can be cultivated under cover conditions when outdoor temperatures are not favorable. The total world production of tomato is 161.7 million metric tons with a value of ∼$59 billion. USA tomato production contributes 13.2 million metric tons with a value of $5 billion to the total world production [2]. The USA ranks in third position in the total world production of tomato after China and India [2]. This paper discusses the early blight (EB) disease and the pathogen, genetic studies and breeding of tomato, problems associated with breeding, QTL (Quantitative Trait Loci) mapping efforts for early blight resistance and prospects to improve breeding for EB resistance
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