Year-end Sale % OFF 
Abstract
Avocado (Persea americana (Mill.)), an important commercial fruit, is severely affected by Phytophthora Root Rot in areas where the pathogen is prevalent. However, advances in molecular research are hindered by the lack of a high-throughput transient transformation system in this non-model plant. In this study, a proof-of-concept is demonstrated by the successful application of Agrobacterium rhizogenes-mediated plant transformation to produce composite avocado plants. Two ex vitro strategies were assessed on two avocado genotypes (Itzamna and A0.74): In the first approach, 8-week-old etiolated seedlings were scarred with a sterile hacksaw blade at the base of the shoot, and in the second, inch-long incisions were made at the base of the shoot (20-week-old non-etiolated plants) with a sterile blade to remove the cortical tissue. The scarred/wounded shoot surfaces were treated with A. rhizogenes strains (K599 or ARqua1) transformed with or without binary plant transformation vectors pRedRootII (DsRed1 marker), pBYR2e1-GFP (GFP- green fluorescence protein marker) or pBINUbiGUSint (GUS- beta-glucuronidase marker) with and without rooting hormone (Dip 'N' Grow) application. The treated shoot regions were air-layered with sterile moist cocopeat to induce root formation. Results showed that hormone application significantly increased root induction, while Agrobacterium-only treatments resulted in very few roots. Combination treatments of hormone+Agrobacterium (-/+ plasmids) showed no significant difference. Only the ARqua1(+plasmid):A0.74 combination resulted in root transformants, with hormone+ARqua1(+pBINUbiGUSint) being the most effective treatment with ~17 and 25% composite plants resulting from strategy-1 and strategy-2, respectively. GUS- and GFP-expressing roots accounted for less than 4 and ~11%, respectively, of the total roots/treatment/avocado genotype. The average number of transgenic roots on the composite plants was less than one per plant in all treatments. PCR and Southern analysis further confirmed the transgenic nature of the roots expressing the screenable marker genes. Transgenic roots showed hyper-branching compared to the wild-type roots but this had no impact on Phytophthora cinnamomi infection. There was no difference in pathogen load 7-days-post inoculation between transformed and control roots. Strategy-2 involving A0.74:ARqua1 combination was the best ex vitro approach in producing composite avocado plants. The approach followed in this proof-of-concept study needs further optimisation involving multiple avocado genotypes and A. rhizogenes strains to achieve enhanced root transformation efficiencies, which would then serve as an effective high-throughput tool in the functional screening of host and pathogen genes to improve our understanding of the avocado-P. cinnamomi interaction.
Highlights
Avocado (Persea americana (Mill.)) is a major tropical fruit along with mango, pineapple and papaya, accounting for approximately two-thirds of the world tropical fruit production
P. cinnamomi isolate GKB4 used in avocado infection experiments was obtained from the culture collection of the Avocado Research Programme, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, South Africa
Of the Agrobacterium treatments alone, ARqua1 was consistent in root induction in both avocado genotypes, across strategies
Summary
Avocado (Persea americana (Mill.)) is a major tropical fruit along with mango, pineapple and papaya, accounting for approximately two-thirds of the world tropical fruit production. In 2014, global avocado production was estimated to be 5.02 million tons of which South Africa contributed 107176 tons [1]. Avocado production is of economic importance to South Africa, as 65845 tons of avocados with a total value of R978 million was exported in 2014 [2]. The most important biotic constraint in avocado production in South Africa is Phytophthora Root Rot (PRR) caused by the oomycete Phytophthora cinnamomi Rands, a pathogen with a broad host range of over 3500 plant species and found in all major avocado producing areas in the world [3,4]. The incidence of PRR across the world has been reported to vary, but can be as high as 90%, leading to wipe out of orchards or significantly limiting fruit production [7]. Chemical control in the form of phosphite spray or trunk injections has extensively been used to control PRR [8]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
