Functional analysis and expression profiling of HcrVf1 and HcrVf2 for development of scab resistant cisgenic and intragenic apples

Apple scab resistance genes, HcrVf1 and HcrVf2, were isolated including their native promoter, coding and terminator sequences. Two fragment lengths (short and long) of the native gene promoters and the strong apple rubisco gene promoter (PMdRbc) were used for both HcrVf genes to test their effect on expression and phenotype. The scab susceptible cultivar ‘Gala’ was used for plant transformations and after selection of transformants, they were micrografted onto apple seedling rootstocks for scab disease tests. Apple transformants were also tested for HcrVf expression by quantitative RT-PCR (qRT-PCR). For HcrVf1 the long native promoter gave significantly higher expression that the short one; in case of HcrVf2 the difference between the two was not significant. The apple rubisco gene promoter proved to give the highest expression of both HcrVf1 and HcrVf2. The top four expanding leaves were used initially for inoculation with monoconidial isolate EU-B05 which belongs to race 1 of V. inaequalis. Later six other V. inaequalis isolates were used to study the resistance spectra of the individual HcrVf genes. The scab disease assays showed that HcrVf1 did not give resistance against any of the isolates tested regardless of the expression level. The HcrVf2 gene appeared to be the only functional gene for resistance against Vf avirulent isolates of V. inaequalis. HcrVf2 did not provide any resistance to Vf virulent strains, even not in case of overexpression. In conclusion, transformants carrying the apple-derived HcrVf2 gene in a cisgenic as well as in an intragenic configuration were able to reach scab resistance levels comparable to the Vf resistant control cultivar obtained by classical breeding, cv. ‘Santana’

Biological, environmental and socioeconomic threats to citrus lime production

Limes as a fruit crop are of great economic importance, key to Asian and South American cuisines and cultivated in nearlyall tropical and subtropical regions of the world. Demand for limes is increasing, driven by World Health Organizationrecommendations. Pests and pathogens have significantly reduced global productivity, while changes in agronomictechniques aim to alleviate this stress. We present here a holistic examination of the major biotic (pests and pathogens) andabiotic (environment and socioeconomic) factors that presently limit global production of lime. The major producers oflimes are India, China and Mexico, while loss of lime production in the United States from 2006 has led many countries inthe Western Hemisphere (Mexico, Costa Rica and Brazil) to export primarily to the USA. The most widespread inver-tebrate pests of lime areToxoptera citricidaandScirtothrips citri. Another insect,Diaphorina citri, vectors both Huan-glongbing (HLB) and Witches Broom of Lime, which are particularly destructive diseases. Developing agronomictechniques focus on production of resistant and pathogen-free planting materials and control of insect vectors. HLB infectscitrus in nearly all growing regions, and has been particularly devastating in Asian citrus. Meanwhile,Citrus tristeza virushas infected over 100 million citrus trees, mainly in the Americas and Mediterranean. Currently, Witches Broom Disease ofLime is localised to the Middle East, but recently it has been detected in South America. The range of its vectors (D. citriandHishimonus phycitis) further raises concerns about the potential spread of this disease. Abiotic threats to limeproduction are also a significant concern; key areas of lime production such as Mexico, India and the Middle East sufferfrom increasing water stress and high soil salinity, which combined with invasive pests and pathogens, may eliminate limeproduction in these areas. To ensure future security in lime production, policy makers, researchers and growers will need toexamine the potential of more resistant lime cultivars and establish novel areas of cultivation