Abstract
Litchi downy blight, a destructive litchi disease caused by Peronophythora litchii, is controlled by intensive fungicide applying. Sources of resistance are used in conventional breeding approaches, but the mechanism is not well understood. Follow-up six years investigation, ‘Guiwei’ and ‘Heiye’ displayed stable susceptible and resistant against to P. litchii, respectively. After 72 hour inoculation, ‘Heiye’ showed few disease spots, while ‘Guiwei’ appeared brown and covered with white sporangia. Germination of sporangia and growth of mycelium in ‘Guiwei’ is more quickly than in ‘Heiye’. Transcript levels were measured at 6, 24, and 48 hour post-inoculation. ‘Oxidation-reduction process’ was dramatically enhanced in ‘Heiye’, which could promote its resistance to pathogen infection. A small ratio (3.78%) of common DEGs indicates that resistant and susceptible cultivars take different strategies to defense against P. litchii. At early infection stage, ‘Heiye’ induced a larger number of genes, including seven receptor-like kinases, which quickly recognized attack of pathogen and led to a rapidly resistance by regulation of degradation of proteasome, transcription factors, and cell wall remodeling. The early DGEs were exiguous in ‘Guiwei’, suggesting a weak response. Once the infection was successful, the resistance was repressed by down-regulated genes involved in phenylpropanoid metabolism, ET biosynthesis and signaling conduction in ‘Guiwei’. In conclusion, quickly recognition and early responses to pathogen, as well as minimal pathogen development and basal expression of resistance-related genes, were correlated with a high level of resistance in ‘Heiye’, while susceptible ‘Guiwei’ suffered massive infection due to lagging response and repressed signal transduction.
Highlights
Litchi (Litchi chinensis Sonn.), a subtropical evergreen fruit tree of family Sapindaceae, originate from South China and has been widely cultivated in more than 20 countries due to delicious and nutritional value[1]
The recognition of pathogen-associated molecular patterns (PAMPs) is by cell membrane embedded pattern-recognition receptors (PRRs), which are either receptor-like kinases (RLKs) or receptor-like proteins (RLPs)
The results indicate that the ‘Heiye’ is a resistant cultivar, whereas ‘Guiwei’ is a susceptible cultivar
Summary
Litchi (Litchi chinensis Sonn.), a subtropical evergreen fruit tree of family Sapindaceae, originate from South China and has been widely cultivated in more than 20 countries due to delicious and nutritional value[1]. After a long time applying, the resistant isolates of P. litchii have been detected in some regions[5] Considering both drug-resistance and environmental impact due to the fungicide applying, breeding of resistant cultivar to control the disease are required. Studies about litchi downy blight have mostly concentrated on biological characteristics of pathogen, chemical control and screening of resistant cultivars in litchi[17,18]. Little is known about the disease resistance-relevant genes involved in the interaction between host and pathogen, which requires exploration into the resistance mechanisms against P. litchii. Differential gene expression was conducted to identify the disease resistance-relevant genes and metabolic pathways involved in P. litchii infection. These genes and pathways will provide a theoretical basis for expounding the resistance mechanism against litchi downy blight in litchi
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