Abstract
Late blight of tomato (Solanum lycopersicum L.) caused by the heterothallic oomycete Phytophthora infestans (Mont.) de Bary, is one of the most destructive and serious diseases of tomato in cool and wet environments. Tomato breeders have developed late blight-resistant tomato lines and cultivars based on Ph resistance genes derived from S. pimpinellifolium, but resistance can be short-lived because P. infestans is highly diverse and can readily develop virulence towards the Ph resistance genes. Studies were carried out to assess the resistance level of four tomato genotypes and 48 wild relatives of cultivated tomato to P. infestans. The highest late blight resistance was detected in S. habrochaites accessions LA1777, LA1352, LA2855, LA1347, LA1718 and LA1295, with disease severities ranging from 4.5 to 13.5%. Interestingly, tomato genotypes containing Ph-2 and Ph-3 had significantly lower disease severity indices compared with the susceptible control 'Super Strain B' when inoculated with a highly virulent isolate. However, when a different isolate was used in 2014, the Ph-2 and Ph-3 containing tomato genotypes were as susceptible as 'Super Strain B'. The overall results demonstrate that LA1777, as previously reported, had a high level of resistance against all isolates of P. infestans and is a useful genetic resource for future tomato breeding programs. Key words: Tomato, late blight, Phytophthora infestans, disease resistance, Ph-genes, Solanum habrochaites.
Highlights
Tomato (Solanum lycopersicum L.) is the fourth most important crop in the world after rice, wheat, and soybean (Nowicki et al, 2013), with global production of 162 million tons and a net value of more than $62 billion in 2014 (FAO, 2017)
Tomato breeders have developed late blight-resistant tomato lines and cultivars based on Ph resistance genes derived from S. pimpinellifolium, but resistance can be short-lived because P. infestans is highly diverse and can readily develop virulence towards the Ph resistance genes
The objectives of this study were to (i) investigate the level of resistance to P. infestans in wild relatives S. habrochaites, S. pennellii, S. pimpinellifolium and S. peruvianum and (ii) determine whether tomato accessions containing late blight resistance genes (Ph-1, Ph-2 and Ph-3) could provide acceptable resistance to P. infestans isolates present in Egypt
Summary
Tomato (Solanum lycopersicum L.) is the fourth most important crop in the world after rice, wheat, and soybean (Nowicki et al, 2013), with global production of 162 million tons and a net value of more than $62 billion in 2014 (FAO, 2017). In Egypt, the tomato crop production value was estimated at $1.7 billion in 2014. Diseases caused by different organisms including fungi, bacteria, virus, and nematodes can limit tomato production. Late blight, caused by the hemibiotrophic oomycete Phytophthora infestans (Mont.) de Bary, is considered a major threat to tomato production in tropical and subtropical regions (Lima et al, 2009; Elsayed et al, 2012). The pathogen attacks all above-ground parts of the plant including leaves, petioles, stems and fruit at any growth stage, causing blights, necrosis, blotches and rots that reduce yield and fruit quality (Lievens et al, 2004). The disease can spread and kill plants rapidly when favorable environmental conditions of high humidity and low temperature (18°C) prevail (Haq et al, 2008; Stroud et al, 2016)
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